No. 454.] STUDIES OX THE PLANT CELL. 749 



brane (hautschicht, ectoplasm) into a process (pseudopodium) 

 which advances and is followed immediately by an inflow of the 

 granular cytoplasm. And the growth of the filaments of the 

 Siphonales and higher Phycomycetes is a pushing forward of 

 the outer plasma membrane followed by the granular proto- 

 plasm, but this growth is slow because the plasma membrane is 

 at all times under the restraint of a cellulose envelope. 



Mention should be made of the remarkable coenocytic zoospores 

 well known in Vaucheria and also described by Thaxter ('95^), 

 for the Phycomycete Myrioblepharis. In Vaucheria the entire 

 contents of the sporangium becomes transformed into an im- 

 mense multinucleate zoospore, the cilia being distributed in pairs 

 above the nuclei. In Myrioblepharis the contents of a spor- 

 angium usually forms four large multiciliate zoospores. 



These zoospores of Vaucheria have often been called com- 

 pound zoospores, and the idea has been expressed that they 

 stand for the cooperative union of many hundreds of zoospores 

 (energids) represented by the nuclei and their respective pairs of 

 cilia. And this explanation of the zoospore of Vaucheria is a 

 part of a broad view, formerly very largely held, that the 

 ccenocyte is an assemblage of energids (uninucleate masses of 

 protoplasm) cooperating in a fused structure. 



The theory of the cooperative association of energids in a 

 ccenocyte (Sachs) has been very much modified. While the 

 nucleus and some other organs of the cell, such as groups of 

 cilia, plastids, etc., are homologous with the same structures in 

 uninucleate cells nevertheless the behavior of the ccenocyte is 

 not the same as a group of cooperating protoplasmic units. The 

 ccenocyte reacts to the usual stimuli in precisely the same man- 

 ner as a uninucleate cell, and must be regarded as physiologi- 

 cally presenting no peculiarities over the latter structure except- 

 ing those of an increased bulk of protoplasm demanding a greater 

 number of nuclei for its metabolic processes. The most impor- 

 tant contribution presented by the ccenocyte to our knowledge 

 of the physiology of the cell is the establishment of the plasma 

 membrane as the region of the protoplasm responsive to the 

 stimuli that determine the form assumed in growth. The con- 

 stant shifting of the nuclei and plastids in the movement of the 



