in the Root- Apex of Phaseolus . 53 
differ among themselves as regards various stains and reagents, are all to 
be regarded as ‘ nucleoli.’ 
(2) That these nucleoli may be composed of plastin (or plastin-like 
substance) only, or of plastin combined with chromatin in varying quantities, 
and that this variation in composition partly accounts for the varied accounts 
which are given of their staining reactions, &c., in various plant-cells (cf. 
Montgomery). 
(3) That in those cases where the chromatin-network is prominent and 
gives a strong reaction for chromatin, the nucleolus may either be absent or, 
if present, may give only a slight reaction for chromatin or none at all, and 
that where the chromatin-thread is not prominent the nucleolus is large and 
gives a strong reaction for chromatin. 
(4) That the nucleolus simply forms a part of the nuclear network, in 
which chromatin or chromatin-substance may be stored, and possibly to 
some extent elaborated, and that it is not therefore an independent organ 
of the nucleus. 
(5) That the nucleolus is concerned in the formation of the chromo- 
somes, and possibly also in the production of the spindle, and that a 
portion of it may in some cases be extruded into the cytoplasm, and 
there disappear. 
(6) That in the reconstruction of the daughter-nuclei the chromosomes 
unite together in a more or less irregular mass or thick thread, out of which 
is evolved the nucleolus and nuclear network, the major part of the chromatin 
passing ultimately into the nucleolus, except in cases where division again 
immediately takes place. 
(7) That the vacuolar structure of nucleoli is general, and may in- 
dicate, either the separation or partial separation of the nucleolar substance 
into plastin and chromatin, or a greater accumulation of chromatin in 
its peripheral layer. 
(8) That Zimmermann’s conclusion, ‘ omnis nucleolus e nucleolo,’ is 
not justified by the evidence before us, and that the nucleolus cannot, in 
the majority of cases at any rate, be regarded as an independent organ 
of the nucleus. 
(9) If these conclusions are correct, it is obvious that the conception of 
the part played by the chromosomes in heredity will have to be modified, 
and, as Dixon has already suggested 1 , the nucleolus, as well as the chromo- 
somes, will have to be taken into account in any new hypothesis that may 
be put forward. 
1 Ann. Bot. xiii, 1899. 
