Divisions in Vicia Faba. 
849 
After the conclusion of the homotype division, while the pollen-grains 
are still grouped in tetrads, the nuclei are small and very dense, with a fine 
reticulum in which the details of the arrangement of the thread are not 
readily made out. 
As the nucleus increases in size the reticulum loosens, and its double 
nature is very evident (Pl. LX 11 , Fig. 24). The nucleus remains in the resting 
stage for some little time, while thewall of the pollen-grain becomes thickened, 
and then mitosis begins and hardly differs except in chromosome number 
from the corresponding process in diploid nuclei. The longitudinal fission 
is clear in all stages (PI. LXIII, Figs. 25, 26, &c.), except that here, as in the 
somatic cells, it may be more or less obliterated when the chromosomes are 
passing on to the spindle (Fig. 27). The metaphases and anaphases differ from 
those of the sporophyte in the narrower spindle (Fig. 28) ; the individual 
chromosome presents the same appearance and shows the same somewhat 
irregular outline (Fig. 29). Longitudinal fission of the daughter chromo¬ 
somes usually appears in the tube nucleus (Fig. 30) a little before it is seen 
in the generative nucleus (Fig. 31). The reticulum (PI. LXII, Fig. 24; 
PI. LXIII, Fig. 31) is quite like that of the sporophyte, though it gives the 
effect of being made up of fewer threads. As in the sporophyte the cross 
attachments break down so that the spireme is double from its formation. 
The nucleolus, sometimes at any rate, persists longer, and may be seen 
(Fig. 25) after the spireme has divided into its constituent chromosomes. 
Discussion. 
The longitudinal fission of the Chromosomes. 
In view of the evidence derived both from the diploid and haploid 
nuclei there seems to us little doubt that in the Bean the separation of the 
chromosomes into two equivalent portions on the spindle is already fore¬ 
shadowed by their fission in the preceding telophase. 
That such a state of affairs is of common occurrence is suggested 
by the observations of Gregoire and Wygaerts (6) on Trilium , of Gregoire ( 7 ) 
and of Merriman ( 10 ) on Allium , and of Digby ( 1 ), who not only studied the 
sporophyte, but also observed parallelisms in the nucleus of the young 
pollen-grain on Gctltonia. 
In Vicia Faba the chromosomes do not appear to break up as in 
Galtonia (Digby ( 1 )), but become joined to one another both end to end 1 
and laterally. In the region of the lateral attachments the sides of the 
split chromosomes are pulled apart, and in this way the network of the 
1 Gregoire lays special stress on his observation that in Allium the ends of the chromosomes 
remain independent; it seems to us very improbable that such is the case in Vicia, for no free ends 
can be identified either in the reticulum or in the spireme stage, except such as inevitably occur in 
nuclei cut by the microtome knife. 
