No. 438.] 



ORIGIN OF THE SPOROPHYTE. 



427 



contains a single nucleus although the fusion of the gamete 

 nuclei is sometimes greatly delayed. The fusion nucleus divides 

 into four nuclei previous to the germination of the spore but 

 some of these degenerate. Thus in Spirogyra three nuclei break 

 down so that only one is left at the time when the new filament 

 ruptures the spore wall. In certain desmids (see Fig. 5) two of 

 the original four nuclei degenerate and the remaining two enter 



zygospore. It may be suggested that the division of the fusion 

 nucleus apparently wasteful of material represents the expendi- 

 ture of energy infused by the sexual act and consequently a 

 sporophyte activity which is necessary to bring the protoplasm 



back to the potentialities of the parent organism. But again we 

 do not know the structural changes that take place in the nucleus 

 of the Conjugates at and after the time of fertilization. Certain 

 diatoms present activities resembling in some respects the Con- 

 jugales but the conditions are too complicated to be given here. 



This attitude towards the significance of the nuclear divisions 

 following the sexual act is the keystone to the theory of the 

 antithetic origin of the sporophyte and its significance, a view 

 held by many prominent botanists including Bower, Strasburger, 

 and Klebs. The sexual act is assumed to give to the fused 

 gametes an organization that will always tend to differ from that 



