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A TEXTBOOK OF THEORETICAL BOTANY 



takes place, whereas the second male nucleus may lose its cytoplasm on its 

 way to the polar nuclei. 



On entry into the embr^'o sac the male nuclei show various forms, 

 spherical, elongate, curved or vermiform. Moreover they seem to change 

 their shape very rapidly and they may lose their variable form and become 

 more spherical as they approach the female nuclei (Fig. 1330). 



D 



H 



Fig. 1330. — hnpatiens !^l(niditlii>eya. Male cells and nuclei in the embryo sac, showing 

 changes in the conformation of the chromatin. A-D, Primary male nucleus. 

 E-H, Secondary male nucleus. Feulgen stain. {After Steffen.) 



StefFen claims that these appearances are those of the chromatin rather 

 than of the nucleus as a whole and that a nuclear membrane may be seen 

 surrounding the curved or spiral chromatin. As this membrane is exceed- 

 ingly delicate and easily overlooked, the descriptions of the nuclei as being 

 vermiform may be erroneous. On contact with the oosphere the male nu- 

 cleus appears to " sink in " or be " immersed " in the oosphere, whose 

 membrane, though very delicate, seems to be fairly firm. No aperture in the 

 membrane has been seen and the nearest simile one can give is that of two 

 oil drops fusing. The oosphere membrane, at least in its lower part, where 

 entry usually occurs, is probably a weak thixotropic gel, which is reversibly 

 solvated by contact with the male nucleus. 



The many accounts of the process differ sharply on the question of 

 whether male cytoplasm enters the oosphere, or not. There is too great a 

 body of evidence each way to be easily dismissed, and genetical data support 

 the belief that male cytoplasm sometimes takes part in fertilization and some- 

 times does not. When it does enter the oosphere it very rapidly ceases to be 

 separately distinguishable. 



The male nucleus then passes through the cytoplasm of the oosphere, 

 presumably also by an autonomous movement. On contact with the female 



