56 



BOTANICAL GAZETTE 



[JULY 





from the condition shown in fig. 15 to that in which the spores 

 are delimited have not been clearly followed. Zoospore forma- 

 tion is evidently a very rapid process. With the possible excep- 

 tion of the cilia, the zoospores are quite fully developed before 

 their escape from the sporange. The vacuole and nucleus are 

 quite well defined (figs. 23, 25). Loewenthal (20) found a vacuole 

 and well defined nucleus in the zoospore of Olpidhim Dicksonii 

 before its escape from the sporange. Barrett observed the vacuole 

 in the zoospore of Olpidiopsis, but apparently did not succeed in 

 staining the nucleus. A cleavage of the sporange cytoplasm pre- 

 vious to zoospore formation is apparent in well stained sections. 

 This cleavage begins at the margin of the sporange, and works 

 toward the central region (fig. 22). The process apparently cor- 

 responds to that described by Harper (16) for Woroninella. 



An interesting variation from this development is of quite 

 common occurrence, but has been observed only in fixed and 

 stained material, probably because it is masked in fresh material 

 by peripheral fat globules in the sporange. Soon after the nuclei 

 begin to enlarge in the stages preceding zoospore formation, one 

 of .them (sometimes several) undergoes an especially rapid develop- 

 ment (figs. 17, 21), becoming separated from the other nuclei by 

 a surrounding portion of denser cytoplasm. This is often quite 

 clearly shown, even in unstained sections. A spore may be clearly 

 delimited about this nucleus, while the other spores are yet in an 

 early stage of development. This spore is much larger than the 

 others formed in the same sporange. All the zoospores are alike 



■ 



in structure, the only marked variation being in size. The forma- 

 tion of several of the large spores in the same sporange is excep- 

 tional (fig. 29). 



When freed in water, the zoospores exhibit a great variety of 

 movement. Often the long cilium, which is quite clearly visible, 

 seems to impede the movement of the zoospore, which exhibits 

 a violent jerking motion. Irregular gyrations are common. Fre- 

 quently a zoospore moves back to the sporange from which it 

 escaped and seems to seek an entrance. At times the zoospores 

 move very rapidly from the field of observation in a direct line. 

 The movements become less vigorous after a time; the ellipsoid 









