Nos. 451-452.] STUDIES ON THE PLANT CELL. 



573 



thread-like structure, which Dangeard calls the rhizoplast, extends 

 from the blepharoplast into the cytoplasm and sometimes ends 

 at the side of the nucleus in a granule (condyle). The-c-ilia 

 grow out from the blepharoplast. This apparatus is not known 

 to bear any relation to centrosomes or to the kinoplasm of 

 nuclear figures present at the time of spore formation. But it 

 should be noted that the blepharoplast is situated directly under 

 if not actually in the outer plasma membrane, which is kino- 

 plasmic. The filamentous connection between blepharoplast 

 and nucleus is probably important, especially since it has also 

 been found in zoospores (Timberlake, : 02, for Hydrodictyon) but 

 we do not even know its developmental history much less its 

 function. Further study will be necessary to make clear possi- 

 ble relations to kinoplasm around the nucleus or to centrosomes. 

 Consequently Dangeard' s comparison of Polytoma to the animal 

 spermatozoon is not convincing for it seems to be established for 

 the spermatozoon that portions of the middle piece at least and 

 the flagellum are derived from a true centrosome. Indeed 

 from the meager evidence now at hand the blepharoplast of 

 Polytoma is as likely to be a structure differentiated from the 

 plasma membrane as to have any relation to the nucleus. But 

 detailed studies on sporogenesis may discover a history more in 

 harmony with that of Hydrodictyon. 



We have summarized a portion of Timberlake's (:O2) account 

 of sporogenesis for Hydrodictyon 

 in the previous section under the 

 head of " Cleavage by constric- 

 tion." We shall consider now 

 certain details. Small spherical 

 bodies are found at the poles of 

 the spindles during nuclear divi- 

 sion in the mother-cell. They are 

 undoubtedly accumulations of kino- 

 plasm and perhaps stand for centro- 

 somes. However they have no 

 polar radiations nor could they be 

 followed between mitoses when the 

 nuclei were in resting conditions. 



FIG. 9. The Zoospore. a, Polytoma; 6, 

 Hydrodictyon ; c, Development in Oedo- 

 gonium. (a, after Dangeard : 01 ; b, Tim- 

 berlake : 02 ; c, Strasburger'92.) 



It is not probable therefore 



