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1903} MITOSIS IN PELLIA 39 
finely granular and suggests a delicate membrane being resolved 
into fibers, rather than a membrane being formed from fibers 
(fig. 4). In our opinion the cap is a delicate layer—a sort of 
Hautschicht—immediately surrounding the nuclear membrane. 
Were it not for the fact that the nucleus retains its form and seems 
to be surrounded by a membrane even after the caps have become 
quite conspicuous, we should conclude that the cap is only the dis- 
tended nuclear membrane. At first the space between the cap 
and the surface of the nucleus is filled with a fluid in which no 
fibers or granules can be detected, but later, after the nuclear 
membrane has broken down, a dense mass of spindle fibers appears 
and occupies the space between the two caps. The caps do not 
seem to be different from those seen in the root tips, as described 
by Nemec (24), Schaffner (28), and others. 
The rays of the aster do not penetrate the caps, but are closely 
applied to them. The aster exerts a strong pull, as may be seen 
during the period of elongation, although the elongation is due, 
in some degree, to pressure from within. 
As in the first mitosis, the spindle in early stages consists of 
two half-spindles (jig. 26). Until the caps become resolved 
into fibers they keep the spindle rounded (fig. 26). The caps 
generally break up into fibers during the metaphase or early 
anaphases, and the poles of the spindle may then become blunt 
or irregular (fig. 27). Occasionally the caps keep the poles of 
the spindle rounded even after rather late anaphases have been 
reached (jig. 28). 
The polar radiations generally disappear at the end of the 
prophases, are absent during the metaphase and anaphases, and 
reappear in the telophase (jigs. 26—29). That portion of the 
spindle which lies between the two caps is undoubtedly nuclear 
in Origin. Itconsists of a very dense mass of yap fibers which 
appear with remarkable suddenness (fig. 20; cf. fig. 
From observations on the nucleolus, we feel sure ot ibis body 
Contributes considerable substance to the growing chromosomes. 
As the chromosomes increase in size, the nucleoli become more 
and more vacuolated, and material which resembles that of the 
nucleoli is often found adhering to the growing chromosomes. 
