286 
R. A. HARPER 
vincing, and yet in Bryophytes, Pteridophytes, and Cycads whose nuclei 
divide without the presence of centrosomes they appear apparently de novo 
as blepharoplasts in the formation of the motile male cells and even in the 
last few preceding nuclear divisions. Such evidence as this is most con- 
vincing, as it seems to me, as to the close interrelations of structure and 
function in protoplasmic organization. I have developed elsewhere the 
idea of the central body as a region of connection between nucleus and 
cytoplasm and for the formation of fibrillar kinoplasm in connection with 
my studies of free cell formation in the ascus. The data as to the behavior 
of the central body in the mildews may be taken as embodying the idea of a 
cell organ which I am here presenting. The central body is a permanent 
structure in the mildew cell. I have beeji able to trace it at all stages of 
their growth and development both sexual and asexual. The central 
bodies arise only by division and when the nuclei fuse the central bodies 
fuse, and yet it seems to me this is no ground for regarding them as life 
units, individuals, in the full sense in which the cell is such a unit; much less 
for regarding the cell structure as an aggregate of such living units. The 
position and relation of th,e central body to the nucleus and cytoplasm in 
free cell formation give the best evidence as to its nature. It is, as noted, 
a region of the cell at which the chromatin of the nucleus and the cytoplasm 
come into specific relations by contact and where fibrillar kinoplasm is 
formed and passes out to form the plasma membrane of the young daughter 
cell, the ascospore. That a granule of some specific chemical compound 
could play such a role it seems to me is by no means so easy an assumption 
as that in this particular region where the nucleus and cytoplasm are so defi- 
nitely connected we have a concentration, a localization, of formative 
processes which results in the production of the disc-like central body and 
the radiating fibrils which ultimately form the plasma membrane of the 
ascospore. The activity of the processes dies down after cell division is 
complete but increases again when a spindle is to be formed for the next 
nuclear division. 
From this point of view it is quite conceivable that, as in the ferns and 
cycads, a central body should appear de novo at the poles of the spindles 
in the androgones, where fibrillar kinoplasm aggregates, and persist later 
as the region from which the fibrillar cilia arise in the metamorphosis of 
the androcyte into the motile antherozoid. 
I have avoided introducing in this connection the still too vague con- 
ceptions of intracellular enzymes and their role in cell activities; but the 
processes of free cell formation in the ascus can certainly be well conceived 
as involving a fermentative katalytic action of the contents of the nucleus 
on the adjacent cytoplasm in the region of the central body which results 
in the diffusion outward from the center of the material of the radiating 
fibrils. 
The central body in its obvious dynamic relations to the other structures 
