3 68 
Gates and Rees. — A Cytological Study of 
It therefore seems clear that the appearance of this hyaline area, which 
is always at one side of the nucleus and in contact with the nuclear 
membrane, is the very beginning of synizesis. Sometimes at this stage the 
nuclear membrane appears to be ruptured as though from internal pressure, 
leaving a small clear area at the point of rupture extending into the cyto- 
plasm. The cause of this condition is obscure. In Fig. 6 the reticulum 
appears to have been drawn away from the nuclear membrane. Figs. 7-10 
illustrate further advance of this contraction. The reticulum is gradually 
withdrawn from the nuclear membrane, sometimes uniformly at all points, 
so that the contracted mass comes to lie in the centre of the nucleus, 
but more usually to one side, where it still remains in contact with the 
nuclear membrane. 
In the early stages leading to synizesis, represented by Figs. 7-10, 
while the nuclear reticulum is undergoing varying degrees of contraction, 
it is at first usually surrounded by an extremely delicate membrane, 
’ probably osmotic in character and much thinner than the nuclear mem- 
brane, which enables the contracting thread work to preserve a more or 
less perfectly spherical form. Delicate threads may be present, connect- 
ing the reticulum with the nuclear membrane (Fig. 9), or no such threads 
may be visible (Fig. 8). These threads may be secondary in origin. When 
present, they apparently tend, by their attachment to the nuclear membrane, 
to give the contracting reticular membrane a wavy outline. Fig. 10 repre- 
sents a slightly different condition which is of more frequent occurrence. 
Here the delicate membrane surrounding the reticulum has apparently 
never been complete in itself, being completed by a portion of the nuclear ! 
membrane to which the threads of the reticulum remain attached, though 
obviously drawn out from their original position. 
In both these cases, whether the reticulum becomes completely free 
from the nuclear membrane or remains attached by one portion, the 
necessary conditions are present for the functioning of an osmotic mem- 
brane enclosing the reticulum. Exactly how this membrane arises we 
do not know. It appears to be a precipitation membrane which is laid 
down after the contraction of the nuclear reticulum has begun to withdraw 
the latter from contact with the nuclear membrane, and hence appears 
where the reticulum comes in contact with the karyolymph. It is possibly 
first formed in contact with the nuclear membrane, and then gradually with- 
drawn from that membrane. In L . Scariola it is usually more conspicuous 
than in lettuce. It is owing to this membrane that the reticulum still 
retains in most cases its spherical outline, the evenness of which is an 
indication of the presence of a limiting membrane. This membrane has 
in fact been clearly observed in a large number of nuclei at this stage, 
and can be readily made out from Figs. 8 and 10. 
The possible manner of functioning of such an osmotic membrane 
