2, 
= 
1903] MITOSIS IN PELLIA 37 
described as a centrosphere by Farmer (9), Strasburger (33), 
and by Davis (7), is often found at the center of the aster. 
The origin and behavior of this structure, which we regard as a 
genuine centrosphere, are rather puzzling. While we assumed 
that it must appear earlier than the rays, and that the rays were 
developed from it, the failure to identify the structure before 
the appearance of the rays, and its frequent absence when it 
might be expected to be present, led to a careful study of the 
subject. The conclusion was reached that the centrosphere 
ives rise to the rays, but that the rays may also contribute 
materially to the substance of the centrosphere. 
Although we have not been able to make any satisfactory 
study of living material, we believe that appearances warrant the 
theory that there is a streaming movement in the rays. Such a 
theory is not entirely new to zoologists. If the theory be true, 
when the streaming is toward the nucleus the centrosphere 
would increase in size, while a continued streaming toward the 
periphery would cause the centrosphere to disappear. In regard 
to the origin of the rays, nothing more definite was determined. 
Finely granular areas, showing a tendency to stain with gentian 
violet, were sometimes seen in earlier stages, but the actual 
formation of rays or centrospheres from these areas could only 
be surmised. These areas do not seem to differ essentially from 
those which we (4) have already observed accompanying the 
male nuclei of Pinus Laricio. In some of Miss Ferguson’s (13) 
figures of the same species and of Pinus rigida the areas approach 
the form of definite centrospheres. The aster appears so sud- 
denly that its mode of development is largely conjectural. In 
a fully developed aster there is usually an increase in the 
diameter of the ray at the centrosphere (jigs. 73 and 16), and 
Occasionally a slight enlargement at the Hawutschicht. An enlarge- 
Ment of the ends of the rays, as shown in fig. 73, is just what 
Should be expected if there is a streaming of material. The 
variability in the size of the rays and their irregularly granular 
Character also favor the theory that they are lines of streaming 
material. The tendency of small nucleoli or microsomes to col- 
lect on the rays, as pointed out by Schaffner (27) in his study 
