246 Carruthers. — Contributions to the Cytology of 
The Third Mitosis. 
The prophases of the third division appear to be passed through very 
rapidly ; the nuclei increase very little in size during the resting stage and 
are very small at the time of the third division. The spindles, however, 
are exceedingly clear, and upon them reappear four chromosomes, at first 
corresponding in shape with those of the second division, but later becoming 
elongated and much curved or bent. 
The chromosomes are at first closely grouped at the equator (Fig. 33), 
but at a slightly later stage they separate, two passing towards each pole 
(Fig. 34). Indications of two bent chromosomes at each pole were obtained 
(Fig. 35), and confirmation of this interpretation is afforded by the mitosis 
in the spore which shows two chromosomes passing to each pole (Fig. 39). 
Although instances in which the chromosome number is visible in the third 
telophase and in the spore or hypothecium are infrequent, yet the sum ot 
the evidence from all these constitutes a strong argument. 
The third mitosis is therefore a typical brachymeiosis. 
Spore Formation. 
Towards the end of the third division the astral fibres are very obvious 
(Fig. 36), and on the break-down of the spindle each nucleus develops 
a beak from which radiations proceed (Fig. 37). These rays completely 
delimit the spore, sweeping round the nucleus until they meet at the oppo- 
site pole (Fig. 38). As the spore wall is formed the nuclear beak elongates 
and finally becomes detached from the wall. 
The nucleus then rounds itself up and the beak disappears. The spore 
nucleus now divides mitotically to form eight secondary nuclei (Fig. 39). 
Although this is the normal method of spore formation, there very fre- 
quently occurs an abnormality whereby the eight nuclei, instead of forming 
spores, divide again. Asci thus formed, containing sixteen to thirty-two free 
nuclei, are of fairly common occurrence (Fig. 41). 
Abnormalities. 
Abnormal hyphae were observed in which the nuclei of the penultimate 
cell had divided before fusion, and a second ascogenous cell was cut off 
(Fig. 40). Proliferation of the penultimate cell to form a second and even 
a third hook also occurs (Fig. 11). Occasionally the nuclei of the asco- 
genous cell fail to fuse, but pass together into the young ascus, and, at the 
stage observed, each was undergoing contraction and giving off a chromatin 
body (Fig. 42). 
Morphology. 
Our knowledge of the developmental stages of the Helvellineae was 
until recently restricted to the Geoglossaceae, and was due in the main to 
the work of Dittrich ( 4 ) on Leotia and Mitrula. He also studied Helvetia , 
