850 
Fraser and Snell .— The Vegetative 
resting stages is produced. Later the cross attachments break down so 
that the spireme consists of the split daughter chromosomes of the last 
division arranged presumably in the same order in which their ends became 
united in the telophase. 
The double arrangement persists till the two halves separate on the 
new spindle, and it is only at one stage even temporarily obscured, namely, 
after the segmentation of the spireme when the chromosomes are passing on 
to the spindle. This is in part no doubt due to a fresh supply of stainable 
substance which has been taken up from the nucleolus, but we have also 
found it useful in this connexion to recall the behaviour of two parallel 
pieces of elastic band : if these are held just touching one another and then 
pulled out by their ends, the sides separate to come together once more 
when the strain is relaxed. But if the now slack pieces are bent or twisted 
their independence is again obvious. So, it appears to us, the taut spireme 
shows a duplication which may disappear when it segments, but which 
is once more obvious when the separate pieces come to lie variously curved 
upon the spindle. It must further be borne in mind that the chromosome 
is split only in one plane, and that from certain points of view the fission is 
therefore invisible. Moreover, in favourable preparations the duplication 
can even now be recognized, and it seems to us very doubtful whether 
complete closure of the split ever occurs. 
The recognition of the longitudinal fission in the chromosome is thus 
carried back from the prophase to the preceding telophase, but the mechanism 
by which it is accomplished is still to seek. Gregoire ( 4 , 5 ) describes the 
fission in the telophase as due to the development of alveoli within the 
chromosome, though he does not connect this process with the subsequent 
duplication of the spireme; and a corresponding explanation has been 
put forward by Stomps ( 13 ), who described a process of vacuolization 
in Spinacia , which divides the chromosomes of the telophase into series of 
parallel lamellae. We have seen no indication of more than one line 
of fission in the Bean, and we are inclined to suggest that the pull of 
the lateral attachments may play an important part in bringing this fission 
about. 
One is driven throughout the study of mitosis in the Bean to visualize 
the chromosomes as somewhat elastic, viscous bands, easily adhering to one 
another, easily splitting in their more fluid interior, but retaining their form 
by reason of the greater density of their surface layer, which, as Livingston 
( 9 ) points out for the ectoplasm, may be differentiated by mere contact with 
the external solution. From such a point of view it will follow that 
the narrow cross attachments, consisting as they must almost entirely of the 
transformed outer layer, may cohere sufficiently to pull asunder, as the 
nucleus expands, the unaltered centres of the chromosomes to which they 
are laterally attached. 
