糜子双受精过程的细胞学观察

糜子(Panicum miliaceum L.)受精的全过程在开花后3小时内完成。开花后20分钟,花粉管到达珠孔,30分钟进入胚囊并释放精子;雌、雄性核融合发生在开花后30分钟至3小时。精核与卵核和极核融合的过程基本相同,但总是先完成与极核的融合。开花后2小时,初生胚乳核形成,随后立即分裂。开花后3小时,合子形成,此时胚乳含两个游离核。开花后8—10小时,合子进入分裂期。合子的休眠期约5—7小时。受精作用属于有丝分裂前配子融合的类型。     

罗汉果双受精过程的细胞学观察

罗汉果（Ｓｉｒａｉｔｉａｇｒｏｓｖｅｎｏｒｉ（Ｓｗｉｎｇｌｅ）Ｃ．Ｊｅｍｅｙ）双受精过程属有丝分裂前配子融合类型,授粉后２４～４８ｈ,花粉管进入胚囊,穿过一个助细胞,放出两个精子。雌雄核融合和雄核与次生核融合同时发生在授粉后６２～７２,雄核与次生核融合速度快于配子融合,７２ｈ后即可见到初生胚乳核分裂。合子中的雌雄核仁在授粉后第５～６ｄ融合,授粉后８～９ｄ合成分裂形成二细胞胚。在双受精过程中,多次观察到有多条花粉管进入胚囊和多精入极核现象。原胚期有附加花粉管从珠孔进入。     

Observations on Fertilization in Sugar Beet

The whole process of double fertilization in sugar beet has been observed, the main results are as follows: About 2 hours after pollination, the pollen grains germinate, the sperms in the pollen tube are long-oval. 15 hours after pollination, the pollen tube destroys a synergid and releases two sperms on one side or at the chalazal end of the egg cell. The sperms are spherical each having a cytoplasmic sheath. 17 hours after pollination, one sperm enters the egg cell, and the sperm nucleus fuses with the egg nucleus rapidly. 21 hours after pollination, the zygote is formed. In the meantime, the primary endosperm nucleus has divided into two free endosperm nuclei. 25 hours after pollination, the zygote begins to divide, forming a two-celled proembryo. The dormancy stage of the zygote is about 4 hours. In the meantime the endosperm is at the stage of four free nuclei. 17 hours after pollination, the sperm nucleus comes into contact and fuses with the secondary nucleus. The sperm nucleus fuses with the secondary nucleus, faster than the sperm with the egg. he first division of the primary endosperm nucleus is earlier than that of the zygote, it takes place about 20 hours after pollination, the dormancy stage of the primary endosperm is about 2 hours. The endosperm is free nuclear. The fertilization of sugar beet belongs to premitotic type of syngamy. From the stage of zygote to the two-celled proembryo, it can be seen that addition- al sperms enter the embryo sac, but polyspermy has not been observed yet.     

Fertilization and Histochemical Investigation on Pulsatilla chinensis (Bung) Regel

Fertilization and variation of protein and starch grains in Pulsatilla chinensis (Bung) Regel have been studied at light microscopic level with histochemical test. Based upon the observations, the main conclusions are summarized as follows: The mature pollen grains are two-celled in which the generative cell shows the stronger protein staining than the vegetative cell. And vegetative cells are full of starch garins. When the pollen tube enters into the embryo sac, one synergid is destroyed, or in a few cases synergids are intact. Occasionally two synergids are disorganized as pollen tube penetrates. However, most of the remaining syuergids break down during fertilization, only in a few cases it remains till early stage of embryo development. The contents discharged by the pollen tube consist of two sperms, which stain intensely blue with protein dyes, a great amount of protein and starch grains. Mature female gametophyte (embryo sac) consists of an egg apparatus, central cell, which has a huge secondary nucleus, and antipodal apparatus which retain in course of fertilization. A few of embryo sac contain two sets of egg apparatus, a central cell with two huge secondary nuclei and two sets of antipodal apparatus. In some nucleoli of the central cell the comb-like structure pattern may be detected clearly. There are 1–2 small nucleoli in some egg cells and central cells. All the cells in embryo sac show protein positive reaction. According to the different shades of the color in cells, its may be arranged in the following order: antipodal cells, synergids, central cell and egg cell. Only a few small starch grains are present near nuclei of central cell and egg cell before fertilization, but no starch grains remain in most of the central cell, the synergids and antipodal cells. The fertilization is of the premitotic type. The fusion of the sexual nuclei progresses in the following order: 1, sperms approach and lie on the egg nucleus and secondary nucleus; 2, sperm chromatin sinks themselves into female nucleus, and male nucleolus emerges with the sperm chromosome; and 3, male nucleoli fuse with the nucleoli of egg nucleus and central cell nucleus, and finally forming the zygote and the primary endosperm cells respectively. Nevertheless, as it is well known, the fertilization completes in central cell obviously earlier than that in egg cell. Though it has been explained in cereals and cotton, in Pulsatilla chinensis the main reason is that nucleolar fusion of the male and female nucleoli in egg nucleus is slower than that in secondary nucleus. And the dormancy of the primary endosperm nucleus is shorter than that of the zygote. In the process of fertilization, histochemical changes are considerably obvious in the following three parts: 1, from the begining of fusion of male and female nuclei to form zygote and primary endosperm cell, Protein staining around female nucleus appears to increase gradually; 2, no starch grains are detected in embryo sac. Though only starch grains are carried in by pollen tube, they are completely exhausted during this period; and 3, near completion of fertilization starch grains appear again in zygote, however, not yet in primary endosperm nucleus till its dividing for the first time. The present study reveals that antipodal cells and synergids seem to play a significant role in nutrition of the embryo sac during the fertilization.     

黑节草双受精过程及胚胎发育的研究

黑节草从传粉到受精约需１３０ｄ,精子在花粉管中形成,胚囊发育属蓼型胚囊,因反足细胞较早退化,故受精前胚囊多只由卵器和中央细胞组成。精卵核融合时,精核染色质进入卵核后凝集成颗粒状,并在原位与卵核的染色质融合,雌、雄性核仁一直维持至合子的第一次分裂期前。双受精作用正常,属于有丝分裂前配子融合类型,初生胚乳核发生２－３次分裂后逐渐退化消失,胚的发育局限于球形胚阶段。     

The Studies on Embryology in Fritillaria ussuriensis Maxim

The development of the anther wall follows Basic-type. The cytokinesis at the time of pollen mother cell meiosis conforms to successive type. The arrangement of the microspores in the tetrad is referred to isobilateral. The primary wall between the generative cell and the vegetative cell is callose. The callose wall is easily detected under the fluorescence microscope. The mature pollen grain is 2-celled type. The ovule is bitegminous, tenui-nucellar and anatropous. The development of the female gametophyte follows Fritillaria-type. The mature embryo sac. consists of the six cells including the seven nuclei. The fertilization is referred to the premitotic syngamy type. The fusion of the female and male nucleoli is not observed at the end of the fertilization. The division of the primary endosperm nucleus is earlier than that of the zygote. The development of the endosperm is referred to nuclear type. The division of the zygote is transverse of longitudinal, the development of the embryo conforms to Onagradtype. When the seed is mature, the embryo is at the proembryo stage without differentiation and the endosperm cells are not absorbed.     

Ovule,Female and Male Gametophyte and Fertilization of Kingdonia uniflora Balfour F. et W. W. Smith

The structure of ovule, female and male gametophyte, double fertilization and the distrubution of starch grains during the fertilization have been studied. The main results are as follows: ( 1 ) Ovule The ovule is anatropous, unitegmic and tenuinucellate. The nucetlus appears cylindric, since megaspores and embryo sac development, its internal cells of nucellus become disorganized, so that only a single layer of epidermal cells remains toward the side of the micropyle, On the other hand, the integument is not as long as nucellus, as a result micropyle is not formed. And no vascular bundle is found in the integument. (2) Female gametophyte The mature embryo sac is slender and is composed of an egg cell, two synergids, a central cell and three antipodal cells. The egg cell is situated slightly away from the tip of embryo sac. Some of them contain starch grains. Synergids occupy the tip of embryo sac. Its wall at micropylar region appears irregular in thickenes and irregular in ingrowths to form the filiform apparatus. The centrateell is very large, and strongly vacuolated Two polar nuclei come to contact closely with each other, but not fuse, or to fuse into a large secondary nucleus before fertilization. The polar nuclei or the secondary nucleus are usually situated at the middle-lower position of the central cell or nearer to the chalazal end above the antipodal cell. It is different from egg cell, no starch grains are found here. In most embryo sacs three antipodal cells are found. They are not as large as those in other plants of Ranunculaceae. But six antipodal cells or the antipodal cell with two nuclei may rarely be found. Like synergid, the wall of them appears not only irregularly thickened, but clearly with irregular ingrowths. In a few antipodal cells the starch garins are usually found near the nucleus. By the end of fertilization, antipodal cells become disintegrated. (3) Male gametophyte Most pollen grains are two-celled when shedding, and rich in starch grains. A few of them contain single nucleus or three-celled. (4) The double fertilization The fertilization of Kingdonia unifiora Balfour f. et W, W. Smith is wholly similar to some plants of Ranunculaceae studied. First, the pollen tube penetrates a degenerating synergid. And the pollen tube discharges its contents with two sperm nuclei into the degenerating synergid cell. One of the two sperms fuses with the nucleus of the egg, and the other fuses with two polar nuclei or the secondary nucleus of the central cell. If one sperm nucleus at first fuses with one of the polar nuclei, and then the fertilized polar nuclei again fuses with other polar nucleus. Secondly, the fertilization of the polar nuclei or the secondary nuclei completes earlier than that of the egg. The primary endosperm nucleus begins to divide earlier than the zygote. It seems that one of the sperm nuclei come to contact with egg nucleus, the other has already fused with polar nuclei or the secondary nucleus. The zygote with a single nucleolus appears until the endosperm with 16–20 cell. Thirdly, before and after fertilization there are one to some small nucleoli in egg nucleus and polar nuclei or secondary nucleus. However they increase in quantity from the beginning of the fusion of male nucleis. These nucleoli quite differ from male nucleoli by their small size, and most of them disappear at the end of fertilization. It may be concluded that the small nucleoli increase in quantity is related to the fusion of male and female nuclei. In the duration of fertilization, in ovule starch distribution is in the basal region of integument. But in embryo sac, onlysome egg cells, or zygotes contain starch grains, a part of which was brought in by pollen tube. Sometimes the starch grains are found in some synergids and antipodal cells. No starch grains are found in the central cell.     

The Fertilization and Early Development of Embryo and Endosperm in Stevia rebaudiana Bertani

The mature embryo sac is surrounded by endothelium tapetum. It is composed or an egg apparatus, one central cell with secondary nucleus, and 1–6 antipodal cells. About the 6th hour after pollination, female and male nuclei fuse with each other. The syngamy occurred almost simultaneously with the fusion of an other sperm nucleus and the secondary nucleus, but the velocity of the latter is faster than that of the syngamy. The fertilization of Stevia rebaudiana Bertani belongs to the premitotic type. About the 8th hour after pollination, primary endosperm nucleus is in mitosis, its dividing orientation may parallel or at right angle to the long axis of the embryo sac, and gives rise to two initial endosperm cells. The first five divisions of the endosperm cells are of synchronism. At the stage of heart-shaped embryo, the endosperm cells show the signs of digestion and absorbed. The endosperm development is of the cellular type. About the 10th hour after pollination, zygote divides for the first time. The division of the zygote is always transverse. The embryo development conforms to the Asterad type.     

Observations on the Developmental Femal Gametophyte and the Process of Fertilization of Amcmum visllosum Lour.

The development of megarametophyte antl the process of fertnization are investigated in detail and the following results are obtained: 1. The development of the embryo sac conforms to Polygonmn type. The pollen tube reaches the base of style about 16 hrs., enters into the ovary, 16–18 hrs. and then it, to the embryo sae, 24–28 hrs. after pollination. 2. Pollezt grains are 2-celed at maturity. 3. When the pollen tube reaehes the mieropylar end, both synergids are intact; but their nueleolus become small. Pollen tube enter the synergid through the filiform apparatus and the synergid is degenerated. 4. Pollen tube discharges two sperms which move towards the egg cell and the secondary nucleus respectively. 5. One sprm fuses with the egg nucleus and another with the secondary nueleus. The proeess of syngamy is siniilar to that of secondary nucleus fusion. Primary endosperm nueleus s formed 30 hrs. after pollination. The zygote is formed 30–62 hrs. after pollination. 6. There is no distinct correlation between the syngamy and secondary nueleus fusion.     

Fertilization and Embryo Development of Populus lasiocarpa Oliv

The double fertilization and embryo development of P. lasiocarpa were studied using cytochemical method for DNA, RNA, polysaccharides and proteins. Stigmas were covered by secretion stained positively with PAS and mercuric bromphenol blue at receptive stage. The pollen grains germinated on the stigma in large quantities 6 hours after pollination. Fertilization started at the 6th days after pollination. The sperm nucleus fused with the secondary nucleus faster than the sperm nucleus with the egg nucleus. The syngamy belonged to peremitotic type. A great deal of starch grains in the embryo sac disappeared during fertilization. The endosperm was nuclear type and becomed a cel 31 days after pollination. The endosperm was characterized by a dense cytoplasm rich in protein. No discrete starch grains were observed in endosperm. Afterwards, the endosperm was consumed by the developing embryo, thus the mature seeds were non-endospermous. The zygote was dormant for 6–8 days. During the dormency, many striking changes took place, and then, the zygotes showed more pronounced polarity. These changes included the shinkage of the large vacuole, the reduced size, the reappearance of large vacuole, the enlarging of the size. The embryogenesis conformed to the Solanad type. The ovules matured into seeds successively 44 days after pollination. The mature embryo was straight. Two cotyledons folded each other.     

Studies on Fertilization in Glycine max

This work studies the whole process of fertilization in Glycine max. The results are summarized as follows: 1. The type of ripened pollen grain of soybean was two-cell type. The generative cell was divided mitotically into two spermatids within the pollen tube. 2. In the 6th hour after self-pollination, the pollen tube entered into the embryo sac and released two sperms. Before the fusion of the male and female nuclei, the cytoplasmic sheath of the spermatids falled off. The cytoplasm of the male gamete did not fuse with that of the egg cell. 3. In the 6th hour after self-pollination, one spermatid nucleus come in contact with the egg nucleus and the other with the secondary nucleus, The contact of the sperimatid nucleus with the egg nucleus was a little earlier than that with the secondary nucleus. 4. The spermatid nucleus entered into the egg nucleus; the chromatic granules of the spermatid despiralized. After the complete fusion of the spermatid nucleus with the egg nucleus, the egg nucleus was darkly stained and the chromonemata increased, afterward the male nucleus appeared. 5. In the 28th hour after self-pollination, the zygote begun the first mitotic division. It took about 20 hours to fuse the male and female gametes, and to form the zygote untile before first mitotic division. It means that the zygote dormancy stage of soybean was about twenty hours. 6. In the 7th hour after self-pollination, the spermatid nucleus fused with the secondary nucleus. The process was similar to that of the spermatid nucleus with the egg nucleus. The chromatic granules gradually despiralized within the secondary nucleus, and the male nucleoli appeared. The velocity of the fusion of the spermatid nucleus with the secondary nucleus was faster than that of the other spermatid nucleus with the egg nucleus. 7. In the 10th hour after self-pollination, the secondary nucleus begun the first mitotic division. 8. The fertilization of soybean was the premitotic type.     

Fertilization of Barley (Hordeutn distichutn L.)

Fertilization of barley has been studied and photographically recorded. The pollen grain germinates almost immediately after attaching itself to the stigma, pollen tube reaches the embryo sac after 20–30 minutes (temperature 26°C). One of the sperms permeates immediately to the oosphere, the other joins polar nuclei migrating from the oosphere to antipodal cells after the discharge of pollen tube content. Fertilization of the polar nucleus occurs in most cases at the antipodal cells which have pronounced haustorial character. In triple fusion polar nuclei do not usually fuse prior to fertilization. However, some exceptions were noted: sometimes the fertilization takes place after the fusion of polar nuclei or during the fusion. Being slower, pre-mitotic fertilization of the egg cell could be studied in greater detail.     

Cytological study of pollen tube growth and early seed development inPetunia inflata

Pollen tube growth from the stigma into the ovule, and the early fruit and seed development following fertilization were examined using fluorescence microscopy, scanning electron microscopy and light microscopy inPetunia inflata. After growing intercellularly in the transmitting tract for 24–36 hr, the pollen tubes emerged into the top part of the ovary cavity and grew along the surface of the septum to reach the ovule. It grew around the furnicle and penetrated the micropyle to enter the embryo sac for fertilization. After fertilization, the endosperm nucleus divided first before the embryo, and the cell wall formation occurred following the division, exhibiting the pattern of cellular type of endosperm development. The first division of the zygote did not occur until 3 days after pollination. At 6 days after pollination, the seeds grew considerably and the endosperm has gone through multiple rounds of cell division. High starch formation in the integument, especially around the embryo sac, was also observed.     

番茄受精作用及其间隔期的研究

利用常规石蜡切片法研究了番茄受精作用的全过程,具体研究结果为:(1)授粉后2 h,花粉粒在柱头上萌发;约2~4 h,花粉管长入柱头,且末端膨大;约8 h后,生殖细胞进入分裂期;并于约两小时后,分裂为两个精细胞。(2)约14 h,花粉管进入子房腔;约18~24 h,花粉管进入胚囊,破坏一个助细胞,并在其珠孔端释放两个精子;随后被释放的精子移到卵细胞与次生核附近。(3)授粉后约30 h精核进入卵细胞;约34 h,精核与卵核融合,并在卵核内出现分散的雄性染色质,进而出现雄性核仁;44~50 h,雌、雄性核仁融合,形成合子;合子的休眠期为10 h左右。60 h之后,合子分裂形成二细胞原胚。(4)约26 h,另一个精子的精核与次生核核膜相贴伏,随后与之融合;约30~34 h,次生核内出现分散的雄性染色质,随之出现雄性核仁;约38~42 h,雌、雄性核仁融合,形成初生胚乳核。约44 h后,初生胚乳核进行有丝分裂,形成两个胚乳细胞。番茄胚乳发育属于细胞型。初生胚乳核无休眠期。(5)精子与次生核的融合比与卵核的融合快。(6)番茄的受精作用属于有丝分裂前配子融合类型。     

Embryology of barley: Time course and analysis of controlled fertilization and early embryo formation based on serial sections

The aim of this work was to determine the sequences and their time schedule in fertilization, embryo and endosperm development in a barley strain grown under controlled conditions. This study involved controlled pollinations and serial sectioning of material embedded in glycol methacrylate.
In Hordeum vulgare cv. Bomi the pollen tube reaches the nucellus in the course of 40 minutes after pollination (m.a.P). In the next minutes the tube advances between the nucellar cells, through the filiform apparatus of the degenerating synergid and releases its contents, which is characterized by rod-shaped starch grains. One of the sperm nuclei is fused with the egg nucleus 45 m.a.P., the second is in contact with the two polar nuclei 50–60 m.a.P., but the real connection between one of the polar nuclei and the sperm nucleus does not occur before 10 hours after pollination (h.a.P.). Triple fusion between all three nuclei takes place about 13 h.a.P. The first division in the zygote takes place 22–24 h.a.P. The embryo has got 3 cells at 34 h.a.P., 4 cells at 38 h. and 52 h.a.P. the embryo is composed of 7 cells. Protoderm formation takes place from a 14-celled embryo stage at 72–80 h.a.P The primary endosperm nucleus divides 14 h.a.P. The next division takes place soon after the first; therefore the endosperm is 4-nucleated already 18. h.a.P. Further divisions are synchronized, and 30–38 h.a.P. there will be more than 32 nuclei. The synchronous divisions continue, and the cellularisation begins at about 70 h.a.P. There is a tight correlation between the enlargement of the ovule and the embryo sac in the first days of the embryo development.     

FERTILIZATION IN BARLEY

The mature embryo sac of barley consists of an egg, two synergids, a central cell, and up to 100 antipodal cells. At shedding the male gametophyte is 3-celled, consisting of a vegetative cell with a large amount of starch and two sperms having PAS+ boundaries. Before pollination the nucleus and cytoplasm of each synergid appear normal. After pollination the nucleus and cytoplasm of one synergid undergo degeneration. The pollen tube grows along the surface of the integument of the ovule, passes through the micropyle, and enters the degenerate synergid through the filiform apparatus. The pollen tube discharges the vegetative nucleus, two cellular sperms, and a variable amount of starch into the degenerate synergid. Soon after deposition the sperms migrate by an unknown mechanism to the chalazal end of the degenerate synergid. Sperm nuclei then enter the cytoplasm of the egg and central cell, ultimately resulting in the formation of the zygote and primary endosperm nucleus, respectively. Sperm boundaries do not enter egg or central cell, but it was not possible to determine the fate of other sperm components. Degenerate vegetative and synergid nuclei remain in the synergid after fertilization, constituting what are considered to be X-bodies in barley. The second synergid degenerates during early embryogeny.     

羊草受精作用及其胚与胚乳早期发育的观察

利用常规石蜡制片方法研究了羊草受精过程及胚与胚乳的早期发育,其主要结果为：(1)授粉后1h,花粉管破坏1助细胞,释放2精子。精子为眼眉状,难以区分其细胞质鞘;(2)授粉后1～2h,2个精子分别移向卵细胞与极核;(3)授粉后2～3h,精核分别贴附于卵细胞与极核核膜上;(4)授粉后3～10h,精核与卵核融合,并出现雄性核仁,形成合子;(5)授粉后3～4h,精核与极核融合,并出现雄性核仁,形成初生胚乳核,精核与极核的融合比与卵核融合快;(6)传粉后20h,合子分裂,合子的休眠期为10h左右;(7)传粉4h,初生胚乳核分裂,初生胚乳核没有休眠期;(8)羊草双受精作用属于有丝分裂前配子融合类型;(9)胚胎发育属于紫菀型,胚乳发育属于核型胚乳。     

Invvestigations on Early Embryogenesis of Actinidia chinensis Planch var. chinensis

This paper deals with early embryogenesis of Actinidia chinensis var. chinensis. 1. Ovary superior consists of 34—45 carpels. Each carpel contains 11–45 ovules. The ovule is uni-integument and tenuinucellar. The ovule is anatropous. The archesporium is formed by a single cell, and directly develops into megaspore mother cell. Sometimes the archesporium consists of 2–3 cells, but only one of them develops into megaspore mother cell and the others are degenerated. 2. The mature pollen grain is two-celled and the embryo sac belongs to olygonum type. In most embryo sacs two polar nuclei are fused before fertilization. One of the synergids was destroyed as the pollen tube penetrated into embryo sac the other one disappeared after fertilization. In most cases the antipodal cells became degenerated in fertilization process, only some remained until the first division of primary endosperm nucleus. 3. In Beijing area the double fertilization of Actinidia chinensis occurred 30–72 hours after pollination. In the fertilization one sperm fused with egg nucleus and the other sperm fused with the secondary nucleus as usual. The fusion of the secondary nucleus with sperm was in advance of the fusion of the egg nudeus. 4. The endosperm is cellular type.     

Light Microscope Study of Pollen Tube Growth, Fertilization and Early Embryo and Endosperm Development in the Avocado Varieties Fuerte and Hass

Pollen tube growth, fertilization and early embryo and endospermdevelopment were studied using light microscopy in the avocadovarieties Fuerte and Hass. The ovule was penetrated by a pollen tube by 24 h after pollination.On reaching the ovary, the pollen tube grew along the surfaceof the inner ovary wall. It then grew around the funicle, throughthe micropyle in the inner integument and between the papillatecells at the apex of the nucellus. It entered the embryo sacvia a synergid. Sperm nuclei were present in the embryo sacat 48 h after pollination and fusion of the polar and spermnuclei took place before fusion of the egg and sperm. The endospermnucleus was the first to divide and cell wall formation occurredfollowing division. The first division of the zygote occurredat 5 or 6 days after pollination. In the variety Fuerte less than 20 per cent of the 1- and 2-day-oldembryo sacs had been penetrated by a pollen tube although tubeswere often observed in the integument or nucellus. In the varietyHass over 60 per cent of the embryo sacs were penetrated. Inwas concluded that low yields of the variety Fuerte may be partlyattributable to the failure of the pollen tube to penetratethe embryo sac. Persea americana Mill, avocado, pollen tube, fertilization, embryo, endosperm     

Cytological Studies of the Double Fertilization in Rice

Detailed studies on the process of double fertilization in rice were conducted in the present work. The results are summarized as follows: 1. In the embryosac 30 minutes after anthesis, the pollen tube has already reached the micropyle in every specimen. In some cases, it has even entered further into the embryosac and discharged its contents, including the two male gametes. 2. 1½ hours after anthesis, the male gamete enters into the egg cell. As soon as it comes in contact with the egg nucleus, it increases in size. 2 hours after anthesis, the male nucleus is found inside the female one. A male nucleolus is now clearly discernible. 3. The male nucleolus is gradually growing until it reaches the size of the female one, and then the fusion of the two takes place. The fusion is generally completed and the zygote is formed 7 hours after anthesis. 4. The first mitotic division of the zygote occurs 9 hours after anthesis. 5. The fusion of the male gamete and the polar nucleus proceeds in a similar way as that of the male and female gametes, but it takes a much shorter time usually being completed within 3 hours after anthesis. 6. The male gamete enters into one of the polar nuclei and reveals its nucleolus which increases rapidly in size and then unites with that of the polar nucleus. As soon as the union is completed, the nuclear membrane between the closely contacted parts of the two polar nuclei disappears and the primary endosperm nucleus is formed. 7. The first mitotic division of the primary endosperm nucleus begins right after its formation. 8. With the fusion of the male and female gametes and the development of the zygote, the mitochondria in the cytoplasm surrounding the nucleus increase in size and number. However, in the central cytoplasm about the polar nuclei they show no notice- able change during the fertilization process. 9. Based on the facts that in the embryosac a secondary pollen tube is often seen in every stage of the fertilization process and that additional nucleoli are also observed sometimes in the egg nucleus, the authors believe that polyspermy most probably exists in rice plants, and that this may be one of the causes of polyploid plants often found in rice field as reported by several authors.