No. 450.] STUDIES ON THE PLANT CELL. 45 1 



the astral rays of the centrospheres in the ascus instead of con- 

 tracting to a center or disappearing in the cytoplasm after the 

 last mitosis grow around the nucleus and cut out a portion of 

 the cytoplasm to form the spores, thus contributing their sub- 

 stance to a plasma membrane. 



There is little doubt that kinoplasmic fibrillas actually exist as 

 structural elements in the protoplasm. Their growth and move- 

 ment in the cytoplasm and nuclear cavity, their multiplication 

 and shifting arrangements as the spindle develops, and their 

 contraction to the poles of the spindle or to a cell plate give 

 these fibers an individuality that cannot be explained on the 

 theory that they merely represent lines of force or paths of 

 dynamic stimuli. They apparently perform all the activities 

 mentioned above by virtue of their own structural organization 

 which is that of rows of microsomata and in this organization 

 resemble and are probably closely related to cilia. There is an 

 excellent discussion of this subject by Allen, : 03, p. 302, etc. 



Some authors believe that there is a streaming movement in 

 the astral rays (Chamberlain, : 03, for Pellia) either towards or 

 away from the pole of the spindle. This view is founded on the 

 granular appearance of the radiations which are sometimes very 

 thick in Pellia and enlarge at the points where they join the 

 centrospheres or the outer plasma membrane. It is not alto- 

 gether clear that the larger of these structures are quite the 

 same as spindle fibers since they seem to be actually strands of 

 cytoplasm rather than fibrillae. 



It is probably safe to assume that the forms which kinoplasm 

 takes have relation to dynamic activities, but it is not easy to 

 define these. Thus centrosomes, centrospheres and kinoplasmic 

 caps may well be the centers from which dynamic stimuli extend, 

 and they may be the focal points of other energies. These 

 problems have been very little investigated among plants. It is 

 obvious that differentiated regions of kinoplasm have important 

 physical relations to other portions of the protoplasm, one of the 

 most important being the anchorage which they give to fibrillas, 

 thereby largely governing the direction of such strains as come 

 about through the contraction of these structures in the later 

 periods of mitosis. 



