637 
the Meiotic Divisions of Vicia Faba. 
equatorial plate, a nuclear membrane cannot be identified, and the vacuole 
is represented only by a light area around the chromosomes (Fig. 1 8). 
Meantime the encroaching cytoplasm gives rise to the spindle. 
Lawson (6, 7 ) has regarded similar phenomena as evidence that the 
nuclear membrane becomes ‘ closely applied ’ 1 to each of the gemini, so 
that there are formed ‘ as many osmotic systems as there are bivalent 
chromosomes \ 2 For him the nuclear membrane never disappears, and the 
spindle fibres do not intrude into the nuclear system but are attached to 
the nuclear membrane where it is wrapped around each chromosome. 
In Vicia Faba no evidence could be obtained that the nuclear membrane 
as a definite entity ‘completely envelops’ 3 each of the gemini. If we 
choose to define the nuclear membrane as the inner limit of the cytoplasm 
wherever it abuts on nuclear material, we may be justified in using this 
term to indicate the area of contact between the surrounding cytoplasm 
and each individual chromosome, when at last the nuclear vacuole has 
begun to disappear. On such an interpretation, Lawson’s description may 
be applied to this plant, but it is impossible to regard the area of contact 
of the chromosomes and cytoplasm as in any special way related to the 
limiting layer of the vacuole, much less as identical with it. The term 
nuclear membrane seems more appropriately restricted to the latter. 
At about this time also the nucleolus disappears. In the early pro- 
phase it is in close relation to the developing chromosomes, to which it 
apparently gives up a part of its contents. On the heterotype spindle, and 
during the homotype division, a number of deeply staining granules are 
present, and these, no doubt, represent the remains of the nucleolus. 
A nucleolus is not formed in the brief resting stage between the heterotype 
and the homotype divisions, but nucleoli again appear (PL XLIV, Fig. 31) as 
soon as the latter mitosis is complete. 
The Chromosomes on the Spindle. 
The gemini, after they are set free, assume the familiar oval and 
twisted forms. Single and double figures of eight apparently occur in every 
nucleus (e. g. Figs. 18, 1 9) , and various more or less elongated loops may also 
be observed. There is considerable regularity in the appearance of the same 
figures in different nuclei, but there is not enough variety of form to repay 
a special study of this point. 
The gemini are always attached to the spindle by one end (never by 
the middle), in such a way that the two sides of the loop or twist — that is to 
say, the two homologous chromosomes — are both in contact with the spindle 
and both stand right out from it more or less coiled round one another 
(Fig. 19). Very soon they begin to move apart, producing a U-shaped 
1 Lawson ( 7 ), p. 616. 2 Lawson (6), p. 144. 3 Lawson ( 7 ), p. 616. 
