No. 463.] STUDIES ON PLANT CELL.— VI. 465 



fusion of the gamete nuclei would give material for a larger and 

 more highly differentiated nuclear figure in the first cleavage of 

 ■ the egg. 



Williams' ( : 04b) observations and conclusions on Dictyota 

 are especially interesting in this connection for he shows that the 

 first cleavage-spindles in the parthenogenetic eggs are intranu- 

 clear and multipolar, showing no dominant kinoplasmic centers 

 while the fertilized eggs form each a well differentiated centro- 

 sphere with radiations, exterior to the nuclear membrane, which 

 clearly giiides the whole process of spindle formation. Williams 

 does not hold that this centrosphere comes as an organized struc- 

 ture from either sperm or egg but is developed de novo by the 

 fusion nucleus as the result of the general stimulus of fertiliza- 

 tion. The evidence, then, furnished by studies on fertilization 

 in plants, indicates that the chromosomes alone maintain mor- 

 phological independence throughout the process of fertilization 

 and that the kinoplasmic (archoplasmic) elements play no part in 

 the phenomena as fixed morphological structures but simply con- 

 tribute their substance to the general union of cytoplasm with 

 cytoplasm, and that any specialized kinoplasmic structures of the 

 first cleavage spindle are formed de novo. While it is true that 

 the sperm brings to the egg much kinoplasm it may well be 

 questioned whether such kinoplasm is a necessary factor in the 

 formation of the first cleavage-spindle. It seems more proba- 

 ble that the development of achromatic structures in the first 

 mitosis following fertilization is due rather to the general stimu- 

 lus of cell and nuclear fusion than to particular structures sup- 

 plied by either sperm or egg. 



The second phase of Strasburger's theory of fertilization con- 

 cerns a separation of the two processes in the sexual act : ( i ) 

 the mere growth stimulus, "vegetative fertilization," that may 

 be expected with the. union of any two masses of protoplasm, 

 and (2) the clearly defined sexual phenomena, "generative fer- 

 tilization," which lies in the union of germ plasm of different 

 parentage and diverse potentialities and which leads to the 

 inheritance of these characteristics. It seems clear that the two 

 processes are really present and can be clearly distinguished. 

 But it may be strongly questioned whether the factors charac- 



