540 Lewis . — The Behaviour of the Chromosomes 
plete resting nucleus is formed (Fig. 24). The chromatin now exists in the 
state of rather large irregular lumps connected by linin threads, the whole 
presenting an appearance not strikingly different from the resting nucleus of 
the spore-mother-cell of the first mitosis (Fig. 25). 
The question quite naturally arises at this point as to the possibility of 
the complete re-formation of the granddaughter segments during the homo- 
typic mitosis ; also as to the meaning of the longitudinal fission of the pro- 
phase and the relation which it bears, if any, to the fission which occurs 
during the anaphase. It has been quite generally assumed that the fission 
which occurs in the chromosomes as they pass to the poles is but the re- 
appearance of that which takes place during the prophase, but it will be 
remembered that this former fission had apparently entirely disappeared at 
the time of the final shortening and thickening of the chromosomes, so that 
only a theoretical basis exists for such a supposition. Those investigators 
who believe in the morphological continuity of chromosomes are not willing 
to admit that a complete resting stage is reached between the two mitoses, 
but nothing can be clearer than that such is the case in Pinus , as was pointed 
out by Miss Ferguson and confirmed in this work for both Pinus and Thuja. 
The Homotype Mitosis. 
The nucleus remains in this condition but a short time when there are 
once more signs of the formation of a spirem. Many of the delicate anas- 
tomosing strands are drawn in and the chromatin becomes evenly dis- 
tributed along the connecting threads, in which case a rather broad spirem 
is formed. This spirem is never entirely complete, as there are always 
many folds and occasional cross branches (Fig. 26). It is always, however, 
a single cord. Miss Ferguson states that this spirem during its final seg- 
mentation into chromosomes forms in loops across the spindle fibres, and 
that as cross-segmentation takes place the loops undergo longitudinal 
fission, and that accordingly two U-shaped segments are formed from each 
loop. These daughter segments then separate completely and form the 
chromosomes of the homotype mitosis. I have examined many nuclei in 
all stages of this mitosis in both Pinus and Thija with this one point con- 
stantly in mind, but have never been able to find any evidence at all con- 
vincing that such a condition occurs in either genus. The spirem is formed 
as a single cord and so it always remains. The chromosomes are formed 
by cross-segmentation of the spirem (Fig. 27). The shape of the chromo- 
somes vary considerably. They are generally, however, rather long rods, 
either straight or hooked at the end, or bent in the middle. The compound 
curve is occasionally met (Figs. 27, 28). 
Before cross-segmentation has taken place the nuclear membrane has 
disappeared, and spindle fibres crowd into the cavity (Fig. 26). The spirem 
then segments transversely into the chromosomes. These chromosomes 
