45 
in the Root- Apex of Phaseolus . 
given of the structure and staining and chemical reactions, may be due 
to the fact that nucleoli at different stages of their development, or from 
different plants, may vary as to the relative amounts of plastin and chro- 
matin substance which they contain. It seems almost certain that there 
are nucleoli which do not contain any chromatin or very little (the plas- 
masomes, true nucleoli, & c., of various observers), and others which contain 
a large quantity of chromatin (the so-called chromatin-nucleoli, nucleoles- 
noyaux , &c.), and between these two extremes we may have nucleoli with 
varying relative amounts of the two substances 1 . Miss Ferguson mentions, 
in her paper on Pinus Strobus (Ann. Bot., 1901, p. 433), that ‘ the 
occurrence of unstained nucleoli in the same nucleus in which others were 
deeply coloured was common, especially at about the time of synapsis.’ 
Again, ‘ the attitude of this (egg) nucleolus towards dyes varies much 
at different periods of its history. It may or may not take the safranin of 
Flemming’s triple combination ; it may stain intensely with gentian violet 
or iron haematoxylin ; it may show a weak reaction or may be absolutely 
unaffected by them.’ It is not clear from the evidence available that the 
vacuolization of the nucleolus indicates a definite separation of the contents 
of the nucleolus into chromatin and plastin. It is more probable that the 
ground-substance of the nucleolus is plastin, and that the outer layer of 
it may become impregnated with chromatin or a modification of it. 
Changes in the Nucleolus during the Prophase. 
In the resting condition the nucleolus is suspended to the peripheral 
network by delicate threads, which are only visible in carefully stained 
specimens. As the nucleolus increases in size the suspending threads 
become more prominent, and it is then seen that they are intimately 
connected with the nucleolus, appearing as if drawn out of its substance, 
and on the other side are continuous with the peripheral network (Figs. 6 a 
and 7). In Fig. 6 a is seen a nucleolus at this stage which has become dis- 
placed from a nuclear cavity. The connexion of the threads with the 
nucleolus is clearly seen. In the root-apex of Allium Cepa Nemec 2 points 
out that in younger cells the nucleoli are surrounded by a clear space, and 
are connected by achromatic fibres to the nuclear network. The hyaline 
appearance of this space may be simply due to the fact that chromatin- 
granules are absent from these threads. In somewhat older nuclei he 
points out that the radiating threads become more prominent, and chro- 
matin-granules are now seen lying thickly on the surface of the nucleolus, 
and appearing as if fused with its outer layer. His figure illustrative 
of this stage corresponds almost entirely with my Fig. 6, for which I offer 
1 Cf. Montgomery, Woods Holl. Bio. Lectures, 1898. 
2 Ueber die karyokinetische Kerntheilung in der Wurzelspitze von Allium Cepa , Pringsh. Jahrb. 
f. wiss. Bot., xxxiii. 
