Nos. 45I-4S2'] STUDIES ON THE PLANT CELL. 587 



There are numerous problems connected with the physiology 

 of the sperm that bear directly upon its protoplasmic structure. 

 Some of these will be treated in Section IV in connection with 

 processes of fertilization. But at this time it is well to call 

 attention to the intimate association that sometimes exists 

 between the nucleus and blepharoplast. These structures come 

 into actual contact in Cycas and Ginko through a process put 

 forth from the nucleus. It should also be remembered that 

 Timberlake and Dangeard found the blepharoplasts in the 

 ^zoospores of Hydrodictyon and in the cells of Polytoma con- 

 nected with the nucleus by one or two fibers. The nuclear beak 

 that bears the aster in the ascus suggests a similar relationship. 

 These conditions indicate that the activities of locomotion may 

 depend vitally upon the nucleus. 



3. The Egg. 



The subject of fertilization is reserved for the next section 

 (Section IV) of this series and the present account will^ deal 

 only with the structure of the unfertilized egg. As the sperm 

 is derived from a motile gamete identical with the zoospore, so 

 the egg has had a similar origin. We have traced the steps in 

 this evolutionary process among the algae in a former paper 

 (^Popular Science Monthly, Feb. 1903, p. 300). The first indi- 

 cation of a differentiation in the sex of primitive gametes is one 

 of size. The male gametes tend to become smaller while the 

 female contains a greatly increased amount of cytoplasm. One 

 of the important factors determining this differentiation is the 

 number of nuclear divisions which take place in the cells that 

 produce respectively eggs or sperms. There are generally a 

 great many more mitoses in antheridia than in oogonia and con- 

 sequently a given amount of protoplasm must be very much 

 divided to provide each nucleus with its quota of cytoplasm. 



The tendency of oogenesis on the contrary is to conserve the 

 protoplasm for relatively few nuclei, provided for several eggs or 

 for a single nucleus in a solitary e^gg, with the result that the 

 ^gg cell is generally richly supplied with protoplasm. Such proc- 

 esses result in large cells with a prominent chromatophore or 



