No. 450.] STUDIES ON THE PLANT CELL. 461 



a part of this membrane and may start its development, but the 

 final structure must contain very much more material than could 

 possibly be contributed by the sparsely developed spindle fibers . 

 Thus, although the splitting of the cell plate may start the proc- 

 ess of segmentation, its final course and end is probably deter- 

 mined by cleavage through vacuoles, thus utilizing a method 

 characteristic of the thallophytes. 



Chara appears to have a fairly well developed cell plate (Deb- 

 ski, '97) which extends almost entirely across the cell, presenting 

 very exceptional conditions among the thallophytes. This pecu- 

 liarity is in keeping with other characters of the spindle, which 

 begins its development outside of the nuclear membrane and, 

 lacking centrosomes, resembles the nuclear figures of higher 

 plants. It is possible that nuclear studies upon Chara through- 

 out ontogeny might show a variation that would be very signifi- 

 cant for the evolutionary problems concerned with the structure 

 of protoplasm. 



Fairchild ('97) reports a cell plate for Basidiobolus when the 

 beak cells are cut off from the gametes. The structure, as fig- 

 ured and described, is not, however, conspicuous. He points 

 out general resemblances between cell division in this form and 

 in the Conjugales, where, as Van Wisselingh (: 02) described 

 later for Spirogyra, spindle fibers connect the daughter nuclei 

 .and may cooperate towards the end of cell division with a cleav- 

 age furrow from the side of the cell. 



The conditions in the Fucales are not altogether clear. Both 

 Strasburger ('97a) and Farmer and Williams ('98) report that 

 the central spindle disappears in Fucus without the formation of 

 the cell plate and that the wall is developed between the daugh- 

 ter nuclei in a region of granular cytoplasm. However, in Pel- 

 vetia some of the radiating fibrillae from opposite sides of the 

 daughter nuclei bend around these structures and end in the new 

 wall. It is not plain that they contribute much it anything to 

 its formation in the way of substance, but it would seem prob- 

 able that they hold a directive relation to the structure (Farmer 

 and Williams, '98). 



The Sphacelariaceae seem to be somewhat similar to the Fuca- 

 les in their methods of cell division. The beautiful figures of 



