in the Root- Apex of Phaseolus, 33 
of the daughter-nuclei the halves of these two chromosomes again give 
rise to the new nucleoli. 
Whatever may be the exact method of division which takes place, it 
seems clear, as Strasburger says 1 , that we have here a special behaviour of 
the nucleolus in giving rise to the chromosomes which, although opposed by 
Zacharias on micro-chemical grounds, appears to be morphologically decisive. 
According to Golenkin 2 we have a somewhat similar phenomenon 
in Sphaeroplea. The nucleolus breaks up into a number of fragments, 
which arrange themselves in a nuclear disk, and then appear to split up 
and move to the two poles where they fuse into daughter-nucleoli. All 
the chromosomes appear to originate from the nucleolus. He says that 
similar nuclei occur in other green Algae, including all Volvocineae, 
and in Musci. 
Rosen 3 states that in some plant-cells two kinds of nucleoli may be 
present, ‘ Eunucleoli ’ and ‘ Pseudonucleoli.’ The Pseudonucleoli form part 
of the chromatin-network, and are used up in the formation of the chromo- 
somes. The Eunucleoli are like the ordinary nucleoli, and do not disappear 
until a later stage in nuclear division. In the root-apex of Phaseolus there 
is only one kind of nucleolus present, which becomes lobular in the pro- 
phases of division, and does not entirely disappear in some cases until 
the separation of the daughter-groups of chromosomes is completed. 
Macallum 4 has shown that some nucleoli give an intense reaction for 
iron. This indicates that they contain chromatin. He finds in Erythronium 
at least three kinds of nucleoli: — (1) nucleoli which give a weak reaction 
for iron, and which therefore contain little or no chromatin ; ( 2 ) nucleoli 
rich in iron, and which give a reaction for iron in every respect like the 
nuclear thread ; (3) nucleoli found in the embryo-sac. The nucleoli of 
the embryo-sac appear in the filaments during the retrogressive stage as 
spherical elements containing little iron. As the chromatin in the fila- 
ment becomes reduced they give a stronger reaction for iron, and eventually 
are found to consist chiefly of chromatin, ‘and in stained preparations 
appear to contain nearly all the chromatin of the nucleus.’ ‘ When mitosis 
again commences the filament forms at their expense, the increase in size 
of the filament keeping pace, apparently, with the decrease in the quantity 
of chromatin which the nucleoli contain.’ 
V. Hacker considers 5 that nucleoli are not to be regarded as reserve 
1 Loc. cit., 1900. 
2 Bull. Soc. Imp. Nat. Moscou, 1899 C 1 !? 00 )* P« 343* See J. R. M. S., 1901, p. 65. 
3 Beitrage zur Kenntniss der Pflanzenzellen, Cohn’s Beitr. z. Biol. d. Pflanzen, v, 1892, and 
vii, 1895. 
4 On the Distribution of Assimilated Iron Compounds, other than Haemoglobin and Haema- 
tins, in Animal and Vegetable Cells, Q, J. M. S., N. S., xxxviii, 1895. 
5 Praxis und Theorie der Zellen- und Befruchtungslehre. Jena, 1899. Die Vorstadien der 
Eireifung : zusammenfassende Untersuchungen iiber die Bildung der Vierergruppen und das Verhalten 
der Keimblaschen-Nucleolen. Arch. f. mikr. Anat., xlv, 1895, p. 200. 
D 
