On the Systematic Position of Amentotaxus from Its Embryological Investigation

The present paper deals with the embryological study and the systematic position of Amentotaxus argotaenia (Hance) Pilger. The material used was collected during 1980-1981 from Jin-fo Shan, 1400-1600 m, Sichuan Province, China. The species is dioecious. The male cone sheds its pollen during the period from the end of May to the middle of June. The pollen at mature stage is 2-celled. Pollen chamber appears obvious at the end of the nucellus. When pollen grains are dispersed, megaspore mother cell, which is situated deep in the nucellus, is in meiosis. The megaspore divides mitotically after pollination and the free nuclei of female gametophyte divide for the last time at the end of June. The wall formation takes place at the stage of 256 free nuclei. The development of archegonia takes place at the beginning of July and the fertilization occurs about July 20-23. The fertilized egg divides successively four times and results in a 16-nucleate proembryo. The young embryo is developing in August. It is interesting to note that the development of the young embryo is very slow. When the seed reaches the mature stage from June to July in the following year, the multicellular masses of the young embryos resulted from simple polyembryony remain immature within the female gametophyte. No cleavage polyembryony has been found. The subsequent embryogeny takes place after the seed has shed. Keng (1975) considers that Amentotaxus links the Taxaceae with Cephalotaxaceae. Our embryological data support Keng’s conclusion since they share (1) compound microstrobilus, (2) 2-celled pollen grains at shedding stage and (3) the rather long life cycle. Keng (1975) also mentions that Podocarpaceae may connect with Taxaceae through Phyllocladus. According to Keng the Podocarpaceae is related to Taxaceae to certain degree. It is obvious that the primitive spike-like male strobilus like the one in Cordaitales is obviously retained in Podocarpus spicatus and P. andinus of Podocarpaceae and Amentotaxus of Taxaceae. In addition, like in Amentotaxus there are 16 nuclei before wall formation in the proembryo of Podocarpus nivalis. These facts may well indicate that at least the Podocarpaceae and the Taxaceae were derived from a common stock. As far as the Taxaceae is concerned the authors tend to support the view of Koidzumi (1932) that Amentotaxus and Austrotaxus should be put in the same tribe since both possess the spike-like strobilus, the long life cycle and the seed maturation in the following year. They are probably rather primitive genera in the Taxaceae. The proembryogeny of Torreya is more or less specialized. It may be placed in a rather advanced tribe and the tribe Taxeae (including Taxus and Pseudotaxus)may be between the above two tribes. In conclusion, the Taxaceae is related to the Coniferales in certain respects and, as Keng (1975), Harri (1976) and Wang et al. (1979) have pointed out recently, placing of the Taxaceae in Coniferales is rather justifiable.     

A Contribution to Pollination and Fertilization of Amentotaxus argotaenta

The present investigation was conducted during 1980–1982, and mater- ials collected from Jin-Fo shan (Golden Buddha Mountain), at a height of 1400-1600 m, Sichuan province, China. Pollination of Amentotaxus argotaenia began to proceed last week of May, and came into bloom the first week of June. The male strobiles were almost entirely wilting at June 12–15. Thus, florescence of Amentotaxus spread over a period of 3 weeks. While the pollen grains approaching to maturity, most of the microspores divide to form a larger tube cell and a smaller antheridial initial. In this case the mature pollen grains of Amentotaxus consist of two cells. Then pollen grains are attracted down into the pollen chamber in the apex of the nucellus after pollination. The pollen chamber of Amentotaxus in longitudinal section looks like a flask in shape and is very much similar to that of Ginkgo biloba. As pollen grains at pollen chamber begin to germinate, the antheridial initials divide again to give rise to a spermatogenous cell and a sterile cell. At first, the spermatogenous cell is of a size only 11–13 μ in diameter. When the pollen tube reaches the middle part of the nucellus, the spermatogeneous cell is of a size about 30 μ. In the middle of July, pollen tube approaches the top of the female gametophyte. In this time, the spermatogenous cell has already been mature enough and is of 58–85 μ in diameter. The nuclei of spermatogenous ceils, 30–36 μ in size, are usually lying in the lateral side of the cytoplasm at its micropylar end. From the middle to the end of July, spermatogenous cells divide to form two unequal sperms, one of which is larger than the other and is the functional one. The large sperm is almost round in shape and about 56 μ in diameter. The small sperm is elliptic in shape, non-functional, and about 33 μ in diameter. The nuclei of the large and small sperms are about 40 μ and 26 μ, respectively. In some cases there are lateral pollen tube and sperms in the ovules of Amentotaxus, or the pollen tube even grows toward the lower part of female gametophyte in the chalazal end and there are well developed sperms in such a case. In the middle of July, nucleus of the central cell divides to form a ventral canal nucleus and an egg nucleus. The former then breaks down quickly and the latter continues to develope and moves toward the central part of the egg cell gradually. It is interesting to note that there are a number of nucleolus-like grains in the cytoplasm of the egg cell in Amentotaxus. The large nueleolus-like grains contain a larger central vacuole with several smaller vacuoles surrounding it. These grains show a positive reaction and blue colour by PAS and aniline blue black or coomassie brilliant blue, respectively. The above facts show that the nucleolus-like grains contain not only po- lysaccharides, but also protein. Similar grains may also found in the developing pollen tube. This is a unique feature in Amentotaxus and even in Gymnosperms. Otherwise, there are often two groups of the dense cytoplasm under the egg nucleus in Amentotaxus. Fertilization of Amentotaxus took place around July 20–29 (1980–1982). Interval between pollination and fertilization was about two months. After male nucleus fuses entirely with the female nucleus, the zygote begins to divide by mitosis. During fertilization, in addition that the large sperm enters the egg cell and fuses with the egg nucleus, the small sperm, tube nucleus, and sterile cell are often delivered into the egg cell. But they are disintegrated gradual]y and eventually. It is worthy to note that the nucleolus-like grains and the starches in pollen tube are also released into the egg cell. Then enlargement, fusion, and budding in the nucleolus-like grains may be found within the cytoplasm of the egg cell after fertilization. The history of investigating Amentotaxus found in 1883 has been lasting a long period of 100 years. But researches in sex production has never been studied before. The present work has shown that fertilization in Araentotaxus is very much similar to that in Taxus, Pseudotaxus, and Torreya. In other words, they all belong to the same type, that is, mitosis of zygote taking place after fusion of the two sexual nuclei. This condition constitutes one of the features of Taxaceae. But fertilization in Cephalotaxaceae is different from that of Taxaceae in having mitosis taking place before fusion of the two sexual nuclei. Pollination of Amentotaxus is similar to that of Cephalotaxus with dual-cell pollen grains at shedding stage. On the other hand, interval between pollination and fertilization in Austrotaxus lasts for 13.5 months, and this is the longest one in Taxaceae, and it is similar to that of Cephalotaxus proceeding for 14 months. To sum up, from the point of view of pollination, fertilization, and embryogenesis, Amentotaxus could be considered a primitive type in Taxaceae. Perhaps an order of systematic position of the genera belonging to Taxaceae can be arranged thus: Amentotaxus, Austrotaxus, Taxus, Pseudotaxus, and Torreya. And Cephalotaxaceae may be related to Taxaceae by way of Amentotaxus.     

The Development and Structure of the Late Embryo in Torreya grandis

The materials used in this investigation were collected during 1980–1983 from Zhuji county of Zhejiang province, China. Seed of Torrcya grandis is an important dry “fruit” and used for edible oil. It is endemic to China. The primordia of male strobili are differentiated before October in the first year, while those of female strobili occur later. The microspore mother cells and megaspore mother cells are found in March and April in the second year respectively. The fertilization takes place in August and the dormant embryo overwinters at the proembryo stage. Eventually the proembryo begins to differentiate and its development starts in July of the third year. Thus the interval from fertilization to latembryogeny of Torreya grandis lasts for about 11 months. When the seeds of Torreya grandis are shed 'in August the embryo within the seed is still immature. It requires a period of after-ripening. The experiments show that the embryo resumes to develop and differentiate during 1–3 months in stratification in moist sands. The development and structure of late embryo are characterized as follows: 1. The cotyledon of the mature embryo in Torreya grandis is of 15000 μm in length and 87% of the embryo. The hypocotyl is vary shert and only 13% of the embryo. This kind of structure of the embryo in Torreya is very rare among conifers and in some degree similar to that of Keteleeria. When seed is shed the meristem of cotyledon is just differentiated and only 100–200 μm in length at the end of July to the middle of August. As the seeds are stratified in moist sands for 1–3 months, the cotyledon increases about 100 times than in room temperature in Zhuji county. 2. There is a large secretory canal in either side between the procambium and the cortex of the mature embryo. The secretory canal consists of epithelial cells of 4–5 layers. It is very peculiar in conifers. 3. The shoot apex does not begin to differentiate, until the seed has been fallen from the tree. 4. The column of the root cap is rather short and consists of the cells of about 10 layers in height and 6 layers in width. 5. Proteins are only found in the focal zone of the free apex of the young embryo but without any starch grains. The starch is abundantly distributed in the opposite end from the root initials down to root cap and the entire transitional zone. It is interesting to note that neither proteins nor starch grains are found in the suspensor system. It is assumed that the protein may be the main form of storing material in the actively growing cells and tissues of embryo in Torreya grandis.     

Early Embryogeny and Its Starch Distribution in Amentotaxus

The present paper deals with the early embryogeny of Amentotaxus argotacnia (Hance) Pitger and its variation in starch distribution. Amentotaxus is endemie to China. The proembryos of Amentotaxus occurred at the end of July to early August, 1980–1981, When the zygote has sueeessive]y divided for four times, the daughter nuelei are becoming smaller and smaller after each division. At first, the zygote is 80–100 μ in diameter. Then, tbe free nuclei of the proembryo are 50–70 μ in diameter in two-nucleate stage, 36–50 μ in four-nucleate stage, and 29–32 μ in eight- to sixteen-nueleate stage, respectively. The wall formation of proembryos in Amentotaxas as in most other members of Taxaeeae also takes place at 16-nucleate stage. After wall formation the cells u each proembryo are arranged in two groups, upper one constitutes the cells of open tier (O) and the lower one, the primary embryonic eells (PE). The ratio of 0 to PE is 9:7 or 8:8 in some eases. The cells of open tier elongate and divide to form the ceils of upper tier (U) and the prosuspensor eens (S). In such ease, The ratio is U:S:PE= 8:8:8. When the eells of open tier and primary embryonie tier sometimes divide simultaneously, the primary embryo cells result in the embryo cells (E), and the ratio is U:S:E=9:9:14 or U:S:E=8:8:16. The young embryos of Amentotaxus begin to differentiate in the first week of August in Jin-Foshan (Golden Buddha Mountain), 1400 to 1600m. Sichuan Province, China The developmental features of the young embryo in Amentotaxus are as follows: (1) The development of the young embryos lasts for 10 to 12 months. This is very unique in Gymnosperms. The development of tile embryo in Amentotaxus is in some deg ree similar to that of Ginkgo, beeause their young embryos develop in maternal plants, whereas the late embryogeny takes place after shedding of the seed. (2) The young embryos pass through the winter at multieellular stage and the late embryos are still undifferentiated when the arils are getting red and the seeds begin to shed. It is interesting to note that the development of embryos are still staying at embryo seleetion stage of simple polyembryony when seeds were stored for six months in 15-20℃. As far as our information goes, the embryos in seeds should get over another winter until embryo matures. The embryos in Amentotaxus is un;quo in this respect and it is considered to be primitive. Though the seeds of pteridosperms have large female gametophytcs, none of embryos have been found in their fossil seeds. Probably their embryos are not well developed when the seeds mature and shed. Thus the embryos of fossil seeds are not easily preserved (Cronquist, 1968). The condition of embryonic developaleut in Amentotaxus resembles strongly with that in pteridosperms. From above, Amentataxus eould be the most primitive genus in Taxaceae. (3) Simple polyembryony in Amentotaxus is pronfinent. The prosuspensors sometimes divide to give rise to “suspensor embryos”. The general tendency of the starch distribution in male and female gametophytes is that the main regions of stareh are gradually transferred frmn mieropylar to chalazal end wiht the development of the ovule. After pollen germination the stareh proceeds together with the sterile cell, tube nueleus and spermatogenous cell down the arehegonium. In early developmental stage of female gametophyte, the starch region always appears round the upper part of the archegonia; after fertilization they mainly appear in tissue of female gamctophyte near the proembryo or young embryo to form the pyramidal region. It is worthy to note that the starch grains of male gametophyte are larger in size than those of female gametophyte and the former is much less in nmnber than the latter. So far as the embryo proper is concerned the starch grains densely appear armmd the nuclei of the embryos, espeeially those of the prosuspensors. Besides, near the basal part of aril and integument there is a stable region of polysaeeharide which shows the positive reaetion for PAS. This region is always present from the origin of aril to its mature and is an important feature of the ovule and seed in Amentotaxus,     

Megasporogenesis,megagametogenesis, and embryogenesis in Dendrobium nobile (Orchidaceae)

The orchid reproductive strategy, including the formation of numerous tiny seeds, is achieved by the elimination of some stages in the early plant embryogenesis. In this study, we documented in detail the formation of the maternal tissues (the nucellus and integuments), the structures of female gametophyte (megaspores, chalazal nuclei, synergids, polar nuclei), and embryonic structures in Dendrobium nobile. The ovary is unilocular, and the ovule primordia are formed in the placenta before the pollination. The ovule is medionucellate: the two-cell postament and two rows of nucellar cells persist until the death of the inner integument. A monosporic eight-nucleated embryo sac is developed. After the fertilization, the most common central cell nucleus consisted of two joined but not fused polar nuclei. The embryogenesis of D. nobile is similar to the Caryophyllad-type, and it is characterized by the formation of all embryo cells from the apical cell (ca) of a two-celled proembryo. The only exception is that there is no formation of the radicle and/or cotyledons. The basal cell (cb) does not divide during the embryogenesis, gradually transforming into the uninuclear suspensor. Then the suspensor goes through three main stages: it starts with an unbranched cell within the embryo sac, followed by a branched stage growing into the integuments, and it ends with the cell death. The stage-specific development of the female gametophyte and embryo of D. nobile is discussed.

     

Sporophytic apomixis in polyploid Anemopaegma species (Bignoniaceae) from central Brazil

Apomixis and polyploidy have been important in the evolution of the angiosperms, and sporophytic apomixis has been associated with polyembryony and polyploidy in tropical floras. We studied the occurrence of polyembryony in populations of tetraploid Anemopaegma acutifolium, A. arvense and A. glaucum from the Brazilian cerrados, and histological features of sexual and apomictic processes were investigated in A. acutifolium. All populations and species were polyembryonic (68.9–98.4% of seeds). Normal double fertilization occurred in most ovules, with exceptions being that 3% of ovules were penetrated but not fertilized and in 4% of ovules both synergids were penetrated. The penetration of both synergids suggests a continuous attraction of pollen tubes and polyspermy. Adventitious embryo precursor cells (AEPs) arose from nucellar and integumental cells of the ovule in pollinated and unpollinated A. acutifolium, indicating sporophytic apomixis. However, further embryo and endosperm development required pollination and fertilization. This pseudogamy also allows concurrent sexual embryo development. Similar polyembryony rates and polyploidy indicated that A. arvense and A. glaucum are also apomictic, forming an agamic complex similar to that observed for some species of confamilial, but not closely related Handroanthus. The co‐occurrence of apomixis and polyploidy in different groups of Bignoniaceae indicates homoplasious origin of these agamic complexes. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 77–91.     

四倍体双穗雀稗兼性无孢子生殖的研究

研究了四倍体双穗雀稗(Paspalum distichum L)无孢子生殖胚囊、胚胎发育以及假受精特点。当其大孢子母细胞发育至四分体阶段时,大多数情况下会发生四分体退化,同时有多个特化珠心细胞发育为1—3个无孢子生殖胚囊的现象。成熟无孢子生殖胚囊一般3核,包括1个卵细胞和2个极核。卵细胞在抽穗前就能自发分裂形成原胚团,而极核则在抽穗和传粉后参与假受精形成胚乳。当胚珠内存在多个无孢子生殖胚囊时,只是靠近珠孔端的1个无孢子生殖胚囊内的极核与精核结合,而其它的并不参与。种子成熟后出现很低频率的二胚苗。此外,还能观察到少量的有性生殖胚囊的发育以及有性生殖胚囊和无孢子生殖胚囊在同一胚珠中的发育现象,因此判断该类群为兼性无孢子生殖体。     

Embryo development in Cocos nucifera L.: A critical contribution to a general understanding of palm embryogenesis

InCocos (and probably in all other palms) the embryogenesis shows a number of primitive characters, such as differentiation of the embryo proper from one cell of the pluricellular proembryo, origin of the single cotyledon from a position lateral to the terminal stem tip, and a tendency to cleavage polyembryony.     

Observations on the Rate of Early Embryogenesis and Cytomixis in Spring Wheat

The rate of early embryogenesis and cytomixis of spring wheat has been observed. The results obtained are summarized as follows: 2 h. after pollination, the two sperms entered into the egg nucleus and the polar nucleus respectively; after 6 h. triple fusion has been completed, a male nucleolus is discernible in egg nucleus. Twenty-four h. after pollination, 2-celled proembryo can be detectable, after 6 d the differentiation in some embryo has initiated. Three d after pollination, the formation of endosperm cells are proceeding, upto 6 d, the embryo sac are full of endosperm cells. After pollination through full development, the degeneration of the antipodals appears, 4 d later the structure of cell and nucleus disappeared. Only naked nucleoli and chromatin mass are remained. After 8 d the degeneration of antipodals almost has completed. Cytomixis has been seen in the cell of nucellus, endosperms, ovary, proembryo and differentiated embryo and it frequently appeared near the proembryo.     

蚕豆胚珠发育过程中淀粉动态的观察

蚕豆胚珠发育过程中淀粉动态变化如下:1.发育早期,整个胚珠中未见淀粉粒。其后首先在合点区出现淀粉,而后从合点向珠孔逐渐扩大分布范围。2.珠心和内、外珠被中均含有淀粉粒,尤以内珠被的淀粉增长迅速,数量多、个体大。受精后,内珠被解体,淀粉出现在外珠被细胞中,推测营养物质可通过整个胚囊表面进入其中。3.合点与胚囊之间的珠心细胞特化或长形。可能有助于营养物质进入胚囊。4.功能大孢子中贮存丰富的淀粉粒,它和珠心细胞一起是胚囊发育时的营养来源。5.卵细胞受精后,所含淀粉粒的数量和大小明显增长,随着合子和胚细胞的分裂,其中贮存的淀粉逐渐被消耗,到多细胞球形胚时完全消失。6.胚乳核周围始终未出现淀粉粒。7.胚器官分化之后,子叶和胚轴等处逐渐出现淀粉粒,其中生长活跃的结构如生长点、维管束等不贮存淀粉。8.子叶中的淀粉粒含量迅速增加,颗粒特大,是种子内营养物质的最终贮存场所。     

红豆杉科次生韧皮部的比较解剖

在光学显微镜及扫描电镜下,比较观察了红豆杉科Ｔａｘａｃｅａｅ５属即红豆杉属Ｔａｘｕｓ,白豆杉属Ｐｓｅｕｄｏｔａｘｕｓ、穗花杉属Ａｍｅｎｔｏｔａｘｕｓ,榧树属Ｔｏｒｒｅｙａ和澳洲红豆杉属８种植物茎次生韧皮部的结构。其主要结果为：红豆杉科植物茎次生皮部由轴向系统和径向系统两部分构成。轴向系统由筛胞,韧皮薄壁组织细胞,蛋白细胞及韧皮纤维组成;径向系统由韧皮射线构成,但是,在横切面上,各个组成分子的层次有     

THE DEVELOPMENT OF THE SEED OF ABUTILON THEOPHRASTI I. OVULE AND EMBRYO

Winter , Dorothy M. (Iowa State U., Ames.) The development of the seed of Abutilon theophrasti. I. Ovule and embryo. Amer. Jour. Bot. 47(1): 8–14. Illus. 1960.—Abutilon theophrasti Medic, is a widespread annual weed which produces an abundance of seed in capsules which mature within 20 days after pollination. Ovule differentiation may be observed at least 8 days before anthesis when a sporogenous cell becomes evident and 2 integuments are initiated. An 8-nucleate embryo sac is produced from the chalazal megaspore approximately 2 days before anthesis. The outer integument of the mature campylotropous ovule consists of 2 cell layers, the inner integument has 6 to 15 cell layers. The initially free-nucleate endosperm becomes cellular betwen 3 and 7 days after pollination. At maturity a thin layer of gelatinous endosperm encases the embryo. The Asterad-type proembryo of Abutilon has a stout suspensor and develops rapidly. Four days after pollination cotyledons are initiated; 4 days later a leaf primordium is evident. Fifteen days after pollination the embryo, which has essentially completed its growth, consists of a large hypocotyl with root promeristem and root cap at its basal end, and 2 flat, folded, leaflike cotyledons enclosing a small epicotyl at its upper end. The epicotyl consists of an embryonic leaf and a stem apex.     

五唇兰雌配子体发育和胚胎发生的研究

五唇兰的胚珠倒生型,具薄珠心,两层珠被。胚囊发育为双孢子葱型,成熟胚囊８核。从传粉到受精约５０ｄ,正常双受精。胚具５－６细胞的胚柄,种子成熟时胚柄及胚乳核消失,成熟种子只具单层细胞的种皮和一个未分化的珠珠形胚。     

Updating embryonic ontogenesis in Araucaria angustifolia : from Burlingame (1915) to the present

This study addresses gaps in our understanding of pre-fertilization and archegonia development and reinterprets embryonic ontogenesis from Burlingame (Bot Gaz 59:1–39, 1915) to the present based on timescale and structural features allowing us to determine functionally and developmentally accurate terminology for all these stages in A. angustifolia. Different from previous reports, only after pollination, pre-fertilization tissue development occurs (0–13 months after pollination (MAP)) and gives rise to a mature megagametophyte. During all this period, pollen is in a dormant state at the microphyla, and pollen tube germination in nucellus tissue is only observed at the stage of archegonia formation (13 MAP) and not at the free nuclei stage as reported before. For the first time, 14 months after pollination, a fertilization window was indicated, and at 15 MAP, the polyzygotic polyembryony from different archegonia was also seen. After that, subordinated proembryo regression occurs and at least three embryonic developmental stages of dominant embryo were characterized: proembryogenic, early embryogenic, and late embryogenic (15–23 MAP). Along these stages, histochemical and ultrastructural analyses suggest the occurrence of cell death in suspensor and in cap cells of dominant embryo that was not previously reported. The differentiation of meristems, procambium, pith, and cortex tissues in late embryogenic stage was detailed. The morphohistological characterization of pre-fertilization and embryonic stages, together with the timescale of megastrobili development, warranted a referential map of female reproductive structure in this species.     

On the Fertilization of Oryza sativa L. × Sorghum vulgare Pets.

1.The pollen germination of Sorghum vulgate appeared normal on the stigma of the Oryza sativa, but the pollen tubes grew slowly in the style. Some of the pollen tubes may become enlarged in their tips or sometimes bursting, while others have continued to grow and entered the embryo sacs. 2. The growth rate of the pollen tubes varied widely. A few pollen tubes were observed in the embryo sacs of the materials 2 hours after pollination, but most of them entered the embryo sacs much later. 3. The zygote associated with a paucity of endosperm nuclei was observed in the materials 1 day after pollination. The double fertilization and 8–12-celled proembryo associated with a number of the free nuclei of the endosperm appeared with a rather high frequency (10.3%) in the materials 3 days after pollination. Some of them are normal in appearance and others may show more or less abnormalities. 4. No division figure was found except in one single case in which mitoses have occurred in both the proembryo and the endosperm. It is most likely that in such case the proembryo and the endosperm if left intact might develop further. 5. A 80-celled embryo was the biggest one which appeared in the materials 5 days after pollination. In general, no cells were ever formed in the endosperm, except in one instance among the 7 days materials the endosperm became cellular in micropylar end. In all other cases the endosperm either ceased to develop early or disorganized. The disorganized endosperm materials are considered to be utilized by the embryo. 6. In certain instances the free nuclei of the endosperm were not distributed at random. They were not equal in size and might fuse into giant nuclelei. 7. The most striking feature is that in the embryo sacs, in which double fertilization or proembryo and endosperm have occurred, a dark stained pollen tube was commonly present. This fact leads us to the conviction that in general only if a healthy pollen tube entered the embryo sac, double fertilization can take place and further development can proceed. 8. In certain cases the protoplasm of the embryo cells appeared scanty. It is apparently that the normal metabolism of the embryo was disturbed owing to the lack of nutrient, and the death of the embryo ensued. 9. No differentiated embryo was observed and no mature seeds were produced. The materials fixed 12 days after pollination showed a variety of abnormalities and collapses. The authors believe that the failure of seed production of rice X kaoliang was primarily due to the fact that the pollen tubes in the style grew too slowly to reach the embryo sacs in time. The consequence is that the double fertilization took place only in a late stage while the male and female gametes may have already become unhealthy. In addition, in this late stage the stored starch in the maternal tissues having gradually disappeared, the nutrient supply to the embryo sac was therefore limited and the young embryo and endosperm were finally in starvation.     

Allozyme evidence for polyzygotic polyembryony in Siberian stone pine (Pinus sibirica Du Tour)

Approximately 4000 mature seeds from 350 trees in nine populations (12–75 trees per population) of Siberian stone pine were investigated for multiple embryos (polyembryony). Haploid megagametophytes and embryos were genotyped for eight allozyme loci. Eight-yone seeds (2.11%) had more than 1 embryo. Of these, 71 seeds had 2 embryos (1.85%), 6 seeds had 3 embryos (0.16%), 3 seeds had 4 embryos (0.08%) and 1 seed had 6 embryos (0.026%). Allozyme comparison of megagametophytes and embryos could distinquish two types of polyembryony in 56 of the 81 seeds. In 28 seeds (50%) the polyembryony was polyzygotic (independent fertilizations of more than one egg cell in the ovule); 25 seeds (45%) had most likely monozygotic polyembryony (genetically identical embryos resulting from the cleavage of a single proembryo) and 3 seeds had both genetically different and genetically identical embryos. To the best of our knowledge, this is the first genetic evidence for the form of polyembryony in conifer seeds.     

Embryology and embryogenesis of Spiranthes L.C.M. Richard (Orchidaceae): S. spiralis (L.) Cheval and S. aestivalis (Poiret) L.C.M. Richard

Abstract

The various stages of female gametophyte development and embryogenesis in S. spiralis and S. aestivalis are described. In both species the reproductive cycle is sexual. Some peculiarities are present: the female gametophyte is usually 6-7-8-nucleate; after double fertilization a single endospermatic cell is formed; the proembryo appears differentiated and is made up of different cells in the chalazal and micropylar ends; a single basal cell in the proembryo acts as suspensor.     

腊梅的受精作用及胚胎发生

腊梅 (Chimonanthuspraecox)花两性 ,离心皮雌蕊着生在杯状花托上 ,柱头线形 ,干性。花粉经昆虫传播 ,落在柱头上 1d后萌发 ,第 8d从珠孔进入 ,第 1 4d左右完成双受精 ,为珠孔受精。胚乳为核型胚乳 ;初生胚乳核经短暂休眠进行核分裂 ,位于合点端的游离核首先形成细胞 ,并从合点向珠孔端细胞化 ,第 37d胚乳充满整个囊腔。合子经过近 2周的休眠后开始分裂 ,随着胚的发育 ,大部分胚乳降解 ,为胚的发育提供营养。合点端的胚乳细胞则侵入合点珠心组织 ,为胚进一步发育提供营养。其胚胎发生为柳叶菜型。     

腊梅的受精作用及胚胎发生

腊梅(Chimonanthus praecox)花两性,离心皮雌蕊着生在杯状花托上,柱头线形,干性。花粉经昆虫传播,落在柱头上1 d后萌发,第8d从珠孔进入,第14d左右完成双受精,为珠孔受精。胚乳为核型胚乳;初生胚乳核经短暂休眠进行核分裂,位于合点端的游离核首先形成细胞,并从合点向珠孔端细胞化,第37d胚乳充满整个囊腔。合子经过近2周的休眠后开始分裂,随着胚的发育,大部分胚乳降解,为胚的发育提供营养。合点端的胚乳细胞则侵入合点珠心组织,为胚进一步发育提供营养。其胚胎发生为柳叶菜型。     

The ultrastructure of zygotic embryo development in pearl millet (Pennisetum glaucum; Poaceae)

The ultrastructure, morphology, and histology of zygotic embryogenesis in pearl millet (Pennisetum glaucum) were examined using light and electron microscopic techniques. Embryogenesis was initially characterized by the presence of a vacuolated egg cell and zygote. The increased presence of Golgi bodies in the zygote suggested it was metabolically more active than the egg cell. The first zygotic division resulted in a densely cytoplasmic apical cell and a highly vacuolated basal cell. The club-shaped proembryo displayed a large amount of endoplasmic reticulum (ER) and ribosomes, very few lipids, and a continuous gradient of vacuoles from the highly vacuolated basal suspensor cells to the densely cytoplasmic apical cells. The embryo had well-defined parts by 8 days after pollination, including shoot and root meristems, coleoptile, scutellum, provascular system, and the first leaf primordium. Large increases in ER, lipids, starch, and vacuoles occurred in the scutellum during the maturation of the embryo, except in the provascular cells. Throughout zygotic embryogenesis, embryo cells were connected by plasmodesmata except where intercellular spaces occurred. Ultrastructural, morphological, and histological observations of zygotic embryogenesis in pearl millet are in agreement with previous reports for other grass species.