No. 463.] STUDIES ON PLANT CELL.— VI. 459 



somes is reduced with the germination of the sexually formed 

 cell so that the protoplasm returns at once to the potentialities 

 of the gametophyte. It is quite possible that the four zoo- 

 spores produced from the oospore of CEdogonium and the four 

 nuclei found in the germinating zygospores of the desmids and 

 Spirogyra may indicate divisions concerned with reduction 

 phenomena similar to those in the tetraspore mother-cells of 

 Dictyota (which may also be expected in the tetraspore mother- 

 cell of the red algae) and in the spore mother-cell of the higher 

 plants. 



For these reasons we seem to be justified in taking a critical 

 attitude towards the accounts of chromosome reduction at game- 

 togenesis among the thallophytes. The logic of the situation 

 would lead us to expect that every sexual act gives a doubling 

 of the chromosomes and an impulse towards the development 

 of a sporophyte phase in plants which must be worked off before" 

 the protoplasm is in condition to reproduce the parent gameto- 

 phyte. Reduction phenomena should follow then every sexual 

 act. If it takes place immediately with the germination of the 

 sexually formed cell there is of course no sporophyte generation. 

 Because the conception of the sporophyte generation with reduc- 

 tion of the chromosomes at sporogenesis is so clearly established 

 in higher groups, those investigators who claim reduction phe- 

 nomena at gametogenesis must expect their views to be severely 

 scrutinized and accept the responsibility of presenting very clear 

 and convincing proof of their conclusions. The author does 

 not think that this evidence is supplied in satisfactory form by 

 any investigation so far. 



2. Fertilization. 



In Section IV of these 'I Studies " we described the most 

 important phenomena of fertihzation under the caption " Sexual 

 Cell Unions and Nuclear Fusions." It will not be necessary to 

 discuss the facts of the phenomena in detail again. This account 

 will take up the more theoretical aspects of the events of ferti- 

 lization and their relation to other critical periods of ontogeny. 



Plants are in complete agreement with animals in the follow- 



