47 
in the Root-Apex of Phaseohis . 
somes just on point of separation ; Figs. 13, 18, and 19 show various 
appearances of the nuclei at this stage, with an irregularly shaped indefinite 
nucleolar mass surrounded by chromosomes. The chromosomes become 
shorter and thicker, and arrange themselves to form the nuclear plate 
(Fig. 20). The remains of the nucleolus can still be seen, and in 
Fig. 20 there is still visible an indication of its connexion with the 
chromosomes in the faintly stained band between the drawn-out portion of 
the nucleolus-remnant and the chromosomes (cf. Fig. 16). It appears that 
the numerous connecting threads around the nucleolus gradually disappear, 
until only one is left, the nucleolus being drawn out at this point into a kind 
of tail (Figs. 16 and 20). 
It is extremely difficult, however, to be certain of the exact sequence 
of events, as the observations have to be made entirely on stained specimens. 
In many cases the nucleolus appears as if it was becoming directly trans- 
formed into chromosomes (see Figs. 12 and 13), but this I think is due 
to a contraction of the nuclear network around the nucleolus just at this 
time. 
Finally all connexion of the nucleolus with the chromosomes ceases, 
It is now much smaller in bulk, stains less intensely than before, and often 
exhibits a somewhat spongy texture, and at the same time begins to divide 
into two generally unequal portions (Fig. 21) which separate to opposite 
poles of the spindle-figure (Fig. 23). Rosen has already observed this 
phenomenon of nucleolar division in Phaseolus , and similar phenomena 
have been observed in some other plants. These nucleolar remnants are 
also surrounded by a clear space as in the resting nuclei, and in Fig. 22 is 
seen a case in which the single nucleolar remnant left at one of the poles of 
the spindle is surrounded by a clear space across which suspending fibres 
are seen. 
At a later stage these nucleolar remnants entirely disappear, and 
coincident with this the spindle becomes more prominent : the fibres 
increase in number and stain more deeply, so that one might easily con- 
clude that there was some connexion between the two, and that a portion 
of the nucleolus is concerned in the formation of the spindle. 
Reconstitution of the Daughter-nuclei. 
We have now to consider the changes which take place in the chromo- 
somes during the reconstitution of the daughter-nuclei. These have an 
important bearing upon the question of the relation of nucleoli to chromo- 
somes, for it is clear I think, from the observations about to be described, 
that the nucleoli in the daughter-nuclei definitely originate by the fusion of 
the chromosomes, first of all into a number of small nucleolar masses, 
connected together by a deeply stained network, and then by a further 
fusion into the large nucleoli found in the mature cells. 
