BIOSYSTEMATIC STUDIES IN THE BOUTELOUA CURTIPENDULA COMPLEX. III. POLLEN SIZE AS RELATED TO CHROMOSOME NUMBERS

Pollen size statistics are presented for 10 closely related species of Bouteloua and relationships between pollen size and chromosome numbers are presented for 13 populations of 5 species and 3 varieties. With 1 exception, all populations of all taxa conformed to a general pattern of pollen size dependent upon chromosome number. Chromosome numbers varied from 2n = 20 to 2n = ca. 103, with several independent aneuploid series. Statistical analyses were made of pollen size as related to chromosome number in the 3 varieties of B. curtipendula. These data showed that tetraploids (2n = 40) of var. tenuis had significantly greater pollen size and coefficient of variation than diploids (2n = 20) of the same variety. Similarly, aneuploids of var. curtipendula with 2n = 45 to 2n = 64 chromosomes had significantly larger and more variable pollen than tetraploids (2n = 40) of the same variety. Highly significant positive regression coefficients were obtained from analyses of chromosome numbers and mean pollen size, and chromosome numbers and coefficient of variation, for var. curtipendula. Regression coefficients for var. caespitosa populations with chromosome numbers over the hexaploid (2n = 60) level were not significant.     

STRUCTURE AND HISTOGENESIS OF THE EMBRYO OF ACER SACCHARINUM. I. EMBRYO SAC AND PROEMBRYO

Structure of the embryo sac and development of the proembryo of Acer saccharinum L. are described from paraffin sections. The embryo sac is monosporic and identical to the 8-nucleate Polygonum type in all respects. Cell, nuclear, and nucleolar sizes are constant within a narrow range and sharply distinctive for all components of the mature sac. Polar nuclei fuse before double fertilization. The longitudinal axis of symmetry of the egg, zygote, and proembryo is variously oriented with respect to the longitudinal axis of the embryo sac and is determined by the point of attachment of the presumptive egg cell to the sac wall. Subsequent development of the young embryo is responsive to aligning factors within the embryo sac and is collateral with the longitudinal axis of the sac. The first segmentation is transverse to the longitudinal axis of the zygote; the second and third are transverse in the basal cell and longitudinal in the apical cell. Descendants of ci form a short irregular suspensor; ca and m give rise to the apical and basal halves respectively of the embryo proper. The contribution of the proembryonic tiers to the older embryo differs in embryos of different initial orientation. Distribution and orientation of mitosis in the proembryo are shown in two accumulation maps.     

A CYTOCHEMICAL STUDY OF EMBRYO SAC DEVELOPMENT IN STELLARIA MEDIA

Megasporogenesis and embryo sac development in Stellaria media were investigated using cytochemical methods for the demonstration of nucleic acids, proteins, and polysaccharides. RNA concentrations were high in the archesporial cells, low in the megaspore mother cell, and increased again to high concentrations with the formation of the megaspore and 2-, 4-, and early 8-nucleate embryo sac. RNA levels were also high in the egg and primary endosperm nucleus but low in the synergid and antipodal cells. Nucleolar size and vacuolation were indicative of RNA synthetic activity. Protein concentrations were parallel in concentration and distribution to those observed for RNA. Polysaccharides were conspicuously absent from all stages except the synergids and nucellar cells. Feulgen-stained DNA was demonstrable in the antipodal cells, megaspore mother cell, and megaspore cell, but was not visible in the 2-, 4-, or early 8-nucleate embryo sac. Feulgen staining was also absent from the egg and primary endosperm nucleus but was visible in the synergids and antipodals. Histones were difficult to visualize anywhere except in the egg cytoplasm and the nuclei of the antipodals.     

APOMIXIS AND POLYEMBRYONY IN HIEROCHLOË ODORATA

Norstog , Knut . (Wittenberg U., Springfield, Ohio.) Apomixis and polyembryony in Hierochloe odorata. Amer. Jour. Bot. 50(8): 815–821. Illus. 1963.—Hierochloë odorata from Michigan, having 2n = 56 chromosomes, was found to reproduce by pseudogamous fertilization of diploid aposporous embryo sacs. Diploid embryos, 2n= 56, and 5n = 140 ± endosperm occurred together. Megasporogenesis was incomplete, and aposporous embryo sac initials developed directly into 8-nucleate Polygonum type embryo sacs. Microsporogenesis was irregular with univalent, bivalent and multivalent chromosomes in meiosis-I. Dyads and microspores varied between n = 24 and n = 32, and less than 50% of the pollen grains stained with acetocarmine. Two other races of H. odorata are known to occur in North America. They are an apparently infertile type in Canada with 2n = 28, and a perfectly fertile race from coastal Connecticut also with 2n = 28. It is suggested that the H. odorata with 2n = 56 is a derivative of the sterile Canadian race.     

Embryology of JapaneseMitella (Saxifragaceae) and its taxonomic significance

The embryo sac formation, endosperm formation, and embryo development in all species of JapaneseMitella andM. diphylla of North America were studied. Monosporic 8-nucleate embryo sac formation of thePolygonum type was found in all the species. In endosperm formation, the Cellular type was found in all species of sect.Mitellaria, and the Helobial type inM. nuda, M. diphylla, andM. integripetala. The Helobial type inM. integripetala was somewhat aberrant and approximated to the Cellular type. In embryo development, three types were distinguishable in sect.Mitellaria: Type A (most of the species), Type B (M. acerina) and Type C (M. pauciflora andM. furusei var.furusei). Type B is an intermediate type between A and C.Mitella integripetala also shows Type A, and the types ofM. nuda andM. diphylla are similar to Type A, except for the shape of suspensor. From outgroup comparison, Type A is suggested to be primitive and Type C to be most derivative in sect.Mitellaria. The affinity of some species in sect.Mitellaria is discussed from the embryogenic data obtained.     

EMBRYOLOGICAL STUDY OF HERMINIUM MONORCHIS (ORCHIDACEAE) USING CONFOCAL SCANNING LASER MICROSCOPY

The embryology of Herminium monorchis (Orchidaceae) was studied using confocal scanning laser microscopy (CSLM), a new technique for embryological studies. This technique may contribute new information to plant embryology. Herminium monorchis has a monosporic embryo sac development. The mature embryo sac is 8-nucleate. Two integuments, both 2-layered, are formed, but only the inner takes part in formation of the micropyle. Double fertilization takes place. The primary endosperm nucleus does not divide, but remains alive at least at the 3-celled stage of embryo development. The three antipodals do not show any sign of degeneration at this stage.     

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.     

鹤顶兰胚囊发育过程中Ca~（2＋）分布的超微细胞化学定位（英文）

用焦锑酸盐沉淀法对鹤顶兰（Phaius tankervilliae）胚囊发育过程中的Ca2＋状态进行超微细胞化学定位。观察结果发现：功能大孢子时期,珠孔端的胚囊壁上开始出现小颗粒的Ca2＋沉淀,但功能大孢子细胞内未见明显的Ca2＋标记;四核胚囊时期胚囊壁上的Ca2＋沉淀明显增多,液泡膜上有Ca2＋沉淀出现,珠孔处的Ca2＋沉淀颗粒较大;成熟胚囊时期,胚囊壁上的Ca2＋沉淀进一步增多,且胚囊内Ca2＋分布明显增多,且极性明显,珠孔端助细胞、卵细胞比合点端反足细胞有更多的Ca2＋沉淀。鹤顶兰成熟胚囊内Ca2＋积累的来源有：（1）在胚囊成熟前主要由珠被细胞、珠细胞通过胞间连丝向胚囊运输;（2）以沉淀有大量Ca2＋的小泡形式跨过胚囊壁进入胚囊。     

Confocal Microscopic Observations on Microtubular Cytoskeleton Changes During Megasporogenesis and Megagametogenesis in Phaius tankervilliae (Aiton) Bl.

In nun orchid (Phaius tankervilliae (Alton) B1. ) embryo sac development follows the monosporic pattern. Changes in the pattern of organization of the microtubular cytoskeleton during megasporogenesis and megagametogenesis in this orchid were studied using the immunofluorescence technique and eonfocal microscopy. At the initial stage of development the microtubules in the arehesporium were randomly oriented into a network. Later the archesporial cell elongated to form the megasporocyte. The cytoskeleton in the elongated megasporoeyte was radially organized in which microtubules extending from the nuclear envelope to the peripheral region of the cell. The megasporoeyte then underwent meiosis 1 to form a dyad. The dyad cell at the chalazal end was larger than the cell at the micropylar end. Microtubules in the dyad cell were radially oriented. The dyad underwent meiosis to give rise to a linear array of four megaspores (i. e. tetrad formation). The chalazal-far most megaspore survived and became the functional megaspore, which contained a set of randomly oriented microtubules. The microtubules in the other 3 megaspore disappeared as the cells degenerated. The functional megaspore then underwent mitotic division giveing rise to a 2 nucleate embryo sac. The nuclei of the 2-nucleate embryo sac were separated by a set of longitudinally oriented microtubules which ran parallel to the long axis of the embryo sac. Each nucleus in the embryo sac was surrounded by a set of perinuelear microtubules. The gnucleate embryo sac again underwent mitotic division to form a 4-nucleate embryo sac. The division of the two nuclei was synchronous. But the orientation of the division plan of the two spindles was different (i. e. the spindle microtubules at the chalazal end ran parallel with the long axis of the embryo sac and those at the mieropylar end ran at right angle to the axis of the embryo sac). The 4 nuclei of the 4-nucleate embryo sac were all tightly surrounded by randomly oriented microtubules. Later the paired nuclei at the micropylr end and at the chalazal end as well underwent mitotic division in seguence. At this time when the embryo sac had reached the 8-nucleate embryo sac stage. The pattern of organization of the microtubules was very complex. Initially the nuclei were surrounded by a set of randomly oriented microtubules, but after the two polar nuclei had moved to the central region of the embryo sac, three different organizational zones of microtubules appeared, viz: a randomly oriented set of microtubules surrounding each nucleus in the chalazal zone: a set (in the form of a basket) of cortical microtubules which surrounded the vacuoles and the two polar nuclei in the central zone and a loosely knitted network of microtubules surrounding the nucleus that later became the egg cell nucleus in the micropylar zone. The two nuclei that would become the nuclei of the synergids were surrounded by a set of more densely packed mierotubules. Towards far the most micropylar end some microtubules formed thick bundles. The site of appearance of these thick bundles coincided with the site of development of the filiform apparatus. The pattern of microtubule organization after cellularization (i. e. at the beginning of embryo sac maturation) did not change much. The author's results indicated that various patterns of microtubule organization observed in the developing embryo sac of nun orchid reflected the complexity and dynamism of the embryo sac.     

BIOSYSTEMATIC STUDIES IN THE BOUTELOUA CURTIPENDULA COMPLEX. I. THE ANEUPLOID RHIZOMATOUS B. CURTIPENDULA OF TEXAS

Gould , F. W., and Z. J. Kapadia . (A. & M. College of Texas, College Station.) Biosystematic studies in the Bouteloua curtipendula complex. I. The aneuploid rhizomatous B. curtipendula of Texas. Amer. Jour. Bot. 49(8): 887–891. Illus. 1962.—Widespread throughout central U.S. is a rhizomatous form of B. curtipendula that basically is tetraploid (2n = 40). In the southwest the predominant type is a caespitose aneuploid with a high chromosome number (2n = ca. 80 to 2n = ca. 102). The present study has shown the presence of an extensive series of rhizomatous aneuploids in central Texas, with chromosome numbers ranging from 2n = 41 to 2n = 64. The distribution of these plants is centered about the region of overlap in the ranges of the 2 previously mentioned types. Available evidence indicates that the rhizomatous aneuploids have arisen through hybridization of the caespitose aneuploids and the rhizomatous tetraploids.     

Nuclear DNA amount during sporogenesis and gametogenesis in sexual and aposporous buffelgrass

Nuclear DNA amounts (C values) were measured in Feulgen-stained sections of anthers and ovules of sexual plant B-2s (genotype aaaa) and aposporous cultivar Higgins (genotype AAaa) of buffelgrass (Pennisetum ciliare). The mass of the unreplicated nuclear genome of a gamete equals 1C DNA. In both lines, pollen mother cell nuclei were 4C before leptotene; anther wall, dyad, 1-nucleate pollen, and generative cell nuclei were 2C; microspore tetrad, enlarging microspore, and sperm nuclei were 1C. The tapetum persisted as uninucleate cells with 4C DNA. Archespores (2-4C) of both lines initiated meiosis to form megaspore tetrad nuclei with 1-2C DNA. In B-2s, chalazal megaspores (2-4C) formed reduced 8-nucleate Polygonum type embryo sacs, and sacs at 2- and 4-nucleate stages showed distributions with peaks near C1 and C2, corresponding to G1 and G2 cell cycle phases; this is characteristic of active mitosis. Nuclei of 8-nucleate sacs and of eggs and polars were 1C, indicating chromosomes were not duplicated before fertilization. Antipodal nuclei had levels from 1 to 36C, possibly due to polyteny or endopolyploidy. In Higgins, aposporous initials and 2-nucleate embryo sacs showed bimodal distributions of 2n nuclei with peaks at 2C and 4C DNA. Nuclei of newly formed 4-nucleate Panicum type aposporous sacs and of polars were 2C; aposporous eggs stained too faintly for reliable measurement.Names of products are included for the benefit of the reader and do not imply endorsement or preferential treatment by USDA     

An embryological study ofPlatanthera bifolia (Orchidaceae)

Flowers ofPlatanthera bifolia were hand-pollinated and fixed in FPA₅₀ after 2, 5, 7, 14, and 21 days. Ovules, made transparent in Herr's clearing fluid, were investigated using confocal scanning laser microscopy. Pollination initiates the megasporogenesis. Two days after pollination dyads are frequent. Three days later most embryo sacs contain two nuclei. Seven days after pollination the embryo sacs are 4–8-nucleate and some are organized, and a week later all embryo sacs are organized and fertilization takes place. The embryo sac development follows thePolygonum type. Twenty-one days after pollination the egg nuclei have been fertilized and the embryo sacs contain 2- to many-celled embryos. A suspensor is formed during early stages of embryo development but degenerates later. Fertilization of the central nucleus does not lead to endosperm development.     

A CYTOLOGICAL STUDY OF BLACK GRAMAGRASS BOUTELOUA ERIOPODA

Streetman , L. J., and Neal Wright . (U.S.D.A., U. Arizona, Tucson.) A cytological study of black gramagrass, Bouteloua eriopoda. Amer, Jour. Bot. 47 (9) : 786–793. Illus. 1960. The chromosome number, microsporogenesis, embryo-sac development and embryogeny of Bouteloua eriopoda (Torr.) Torr. were investigated. Thirty-four of the 35 accessions had a diploid chromosome complement of 2n=20. One accession had a chromosome number of 2n=28. Meiotic behavior of the 20-chromosome plants was normal, and pollen quality approached 100%. However, metaphase-I and anaphase-I cells of the 28-chromosome plants had up to 8 lagging chromosomes. Pollen quality was approximately 67%; however, the plants were highly sterile. These results furnished evidence of a basic number of x = 10 for the genus Bouteloua. Megagametophyte development was normal, which resulted in an 8-nucleate embryo sac of the “Polygonum” type. Abnormal development of nucellar tissue was not detected, and embryo development did not begin until 12–18 hr. after anthesis. The development of the female gametophyte indicated sexual reproduction. A high degree of morphological variability among and within accessions afforded further evidence for sexual reproduction and suggested that the species was largely cross-fertilized. The proembryo, which began development 12–18 hr. after pollination, lacked a discernible arrangement of cells and sequence of division. The endosperm was free nuclear until 4 days after pollination, when it changed to a cellular form. Differentiation of the proembryo into various embryo structures began 4–5 days after pollination. The embryo matured anatomically 12 days after pollination. Black gramagrass, a perennial range grass native to the desert grasslands of the southwestern United States, is a major species in Arizona, New Mexico, and adjacent parts of Mexico. In many areas of low rainfall this species is the only desirable grass.     

水稻HDAR细胞胚胎学研究─—不定胚的发生和发育

对水稻HDAR胚胎发育过程的进一步研究表明,水稻HDAR中有2．72％（17／434）的不定胚发生和发育。其不定胚起源于胚珠内的珠心细胞。不定胚起始细胞启动分裂时,胚囊发育至2核或4核时期,8核胚囊时期,胚珠内已形成多细胞不定胚结构。随后不定胚细胞不断分裂并逐渐挤进胚囊。开花传粉后,不定胚利用胚乳提供的营养可以继续发育和分化。不定胚可以和合子胚一起发育,有时合子胚败育,不定胚继续发育并分化。讨论了水稻HDAR中不定胚的发生,及其发生远早于合子胚的意义。     

IMPORTANCE OF TIME OF GERMINATION AND SOIL DEPTH ON GROWTH OF PROSOPIS GLANDULOSA (LEGUMINOSAE) SEEDLINGS IN THE PRESENCE OF A C4 GRASS

In an investigation of the causes of the invasion of woody plants into grasslands, competition between seedlings of Prosopis glandulosa Torr. and Bouteloua curtipendula (Michx.) Torr. was examined. Introduction of P. glandulosa into a B. curtipendula neighborhood significantly reduced P. glandulosa dry mass when compared to P. glandulosa growth alone. The greater the time interval from P. glandulosa germination to addition of B. curtipendula, the less interference the grass had on woody plant growth. Reciprocally, the greater the time interval from B. curtipendula germination to addition of P. glandulosa, the more interference the grass had on woody plant growth. Prosopis glandulosa belowground dry mass was <0.02 g (all in the upper 30 cm of soil) when planted after B. curtipendula at any soil depth, but if planted alone its root dry mass ranged from 2 to 8 g depending on depth. Prosopis glandulosa seedling dry mass increased linearly with soil depth, while B. curtipendula dry mass reached a plateau. In general, belowground dry mass of P. glandulosa was distributed throughout the soil depth examined (decreasing with depth), while 80% of B. curtipendula dry mass was found in the upper 30 cm of soil, suggesting a partitioning of soil resources. Data suggest that P. glandulosa and perhaps other shade-intolerant woody species that establish in grasslands do so in disturbances or vegetation gaps. Gaps may close, but by this time woody plant roots are below grass roots, thus partitioning soil resources and reducing interspecific competition.     

SEXUAL AND APOMICTIC REPRODUCTION IN CALAMAGROSTIS (GRAMINEAE) FROM EASTERN NORTH AMERICA

Reproductive mode and chromosome numbers were determined for populations of several species of Calamagrostis from eastern North America. Calamagrostis pickeringii (2n = 28), C. perplexa (2n = 70), C. porteri subsp. porteri (2n = ca. 88–100) and C. porteri subsp. insperata (2n = 56) all have a sexual pattern of megagametophyte formation; the basal megaspore of a tetrad develops into a Polygonum-type embryo sac with proliferating antipodal cells characteristic of the Gramineae. In these four taxa self-incompatability, population structure and infrequent flowering limit seed production; they persist primarily by rhizomes and occupy relatively stable, late-successional habitats. Calamagrostis stricta subsp. inexpansa includes apomictic variants (2n = ca. 104–123)that produce megagametophytes by diplospory; the single archesporial cell divides mitotically to produce an embryo sac appearing identical to those formed by sexual species. The embryo and endosperm develop autonomously from egg cell and polar nuclei, respectively. Some apomictic individuals occasionally produce some pollen and may have the potential for reproducing sexually. Their seed set insured by apomixis, variants of subsp. inexpansa colonize disturbed, open habitats and have achieved wide distributions in glaciated regions of North America. Reinterpretation of relationships among taxa I examined necessitates the following new nomenclatural combinations; C. porteri subsp. insperata (Swallen) comb. nov. is based on C. insperata Swallen; C. stricta subsp. inexpansa (A. Gray) comb. nov. is based on C. inexpansa A. Gray and includes C. lacustris (Kearney) Nash and C. fernaldii Louis-Marie.     

Further Studies on Microtubule Organizational Changes During Megagametogenesis in Rice Embryo Sac

Changes in the pattern of microtubule distribution and organization during megagametogenesis in the embryo sac of rice (Oryza sativa L. cv. IR36) were re-examined using a modified polyethylene glycol sectioning technique before immuno-fluorescence staining of microtubules. In the sectioned materials the pattern of distribution and structural organization of the microtubule cytoskeleton were quite well preserved. Fine details of the patterns of structural changes and re-organization of the microtubule cytoskeleton in the major stages of development during embryo sac megagametogenesis (viz. functional megaspore, uni-nucleate, 2-nucleate, 4-nucleate, 8-nucleate and mature stage) could be clearly observed and easily followed. Some new organizational patterns of microtubules associated with the probable movement and positioning of the polar nuclei were observed.     

EMBRYOLOGY AND DEVELOPMENT OF THE ENDOSPERM HAUSTORIUM OF ARCEUTHOBIUM DOUGLASII

Arceuthobium douglasii develops a dome-like structure, the ovarian papilla, in which 2 megasporocytes are formed. The papilla is not a true ovule, for no integuments are formed, and it is forced aside by the developing endosperm. Megasporocytes are differentiated in the spring, but meiosis does not occur until the following spring. A tetrasporic embryo sac is developed which is 8-nucleate at maturity. Pollination and fertilization occur approximately 13–14 months after initiation of the inflorescence. Only 1 of the 2 embryos develops after fertilization. After fertilization, the embryo sac segregates into 2 parts, one containing the zygote and the disintegrating synergids, the other the primary endosperm nucleus and the degenerating antipodals. This primary endosperm cell elongates toward the base of the ovarian papilla. Cytokinesis then forms an endosperm cell, adjacent to the zygote, and a haustorial cell. The haustorial cell forms several tiers of cells which persist during the development of the embryo and endosperm. The zygote, while still contained within the ovarian papilla, divides, forming a 2-celled sphere. It remains unchanged until after it is conveyed out of the ovarian papilla by the developing endosperm. The development of the embryo and endosperm is arrested in the autumn approximately 3 months after their initiation. They complete their development the following spring and summer.     

Development and structure of the pericarp and seed of Rhus lancea L. fil. (Anacardiaceae), with taxonomic notes

The pedicel of the female flower of Rhus lancea is distinctly articulated and usually carries three bracteoles. In the linear tetrad the micropylar megaspore forms the 8-nucleate embryo sac of the Oenothera-type. The single, bitegmic ovule is anatropous. The ripe, loose, papery exocarp consists mainly of the outer epidermis and a sclerified hypodermis. The mesocarp is not a typical sarcocarp, since the ridges and the inner layers are sclerenchymatous. The endocarp, originating from the inner epidermis, consists of four layers and its structure and microchemistry emphasize the close alliance of Rhus with other genera of the section Rhoideae. The endotestal seed indicates a phylogenetic affinity between the Anacardiaceae and the Burseraceae.