482 BOTANICAL GAZETTE [rECEMBER 



from the periphery and cut into the protoplasm in the form of 

 curved and branching furrows. Finally, the protoplast within 

 the sporangium becomes divided into approximately equal masses, 

 each of which contains a single nucleus. These masses are zoospore 

 primordia, and each develops into a uninucleate zoospore. The 

 nucleus lies first at the center of the zoospore primordium, with 

 plastids lying near the periphery of the cell. The polarity of the 

 cell is clearly established when the nucleus moves toward the 

 peripheral region of the cell, displacing all the plastids in the 

 vicinity, except one which remains near the nucleus. At this time 

 a small granule can be seen lying in the plasma membrane near 

 the nucleus. This granule becomes the blepharoplast, and in a 

 part of the body of the plastid remaining near the nucleus there is 

 later developed a red pigment which makes it look as if the cilia 

 had arisen from the red pigment. 



Thus the polarity of the zoospore is manifested only after the 

 organization of the blepharoplast and red pigment spot in the 

 plastid. Again, after its quiescence, the exhibition of polarity is 

 lost until either the segmentation of the nucleus or the elongation 

 of the cell wall begins. 



ALTERNATION OF GENERATIONS 



HOFMEISTER 



been universally recognized that the Archegoniatae are char- 



definite 



igularly 



this 



the 



In sharp 



unanimous agreement in regard to the 



an alternation of generations in the Archegoniatae, there is a 

 lively contest of contradictory views as to the alternation of 

 generations in the thallophytes. The thallophytes being a loose 

 assemblage of widely diversified types, and investigations on their life 

 histories being far from numerous enough to permit of any generaliza- 

 tion, some still question whether a regular alternation of definitely 

 established generations exists in the group, and if it exists, whether 

 it is to be regarded as homologous or antithetic. 



