22 Overton. — On the Organization of the Nuclei in the 
the structure of these nuclei with that of ordinary somatic ones, but have 
experienced considerable difficulty in identifying with certainty the last pre- 
meiotic divisions. After the formation of the nuclear membrane, and during 
the period of nuclear enlargement, the chromatic material becomes rather 
regularly distributed in the nuclear cavity, the greater portion of the stain- 
able substance lying in the prochromosomes, each suggesting by its form 
and size that it is derived from a chromosome of the preceding telophases. 
I am not prepared to discuss the problem as to how the chromosomes of 
the telophases are modified in passing over into the resting nucleus. 
Whether the process in germ cells is different from that in vegetative 
divisions certainly needs investigation. Gregoire and Wygaerts (’03) have 
claimed that in vegetative divisions the nucleus possesses an alveolar 
structure, a ‘ reseaux de reseaux ’, which arises by a progressive and irregular 
alveolization and anastomosing of the chromosomes of the telophase. 
According to Gregoire and his students the chromosomes are again formed 
in the prophases of division by a progressive recondensation of the chromatic 
reticulum to form the chromosomes. Haecker (’04) also observes that in 
Siredon the chromosomes, during the telophases, possess alveoli, which 
increase in size and number, finally leading to complete alveolization. 
In Thalictrum purpurascens there is present in the nucleus at this period 
of greatest chromatic distribution a fine, more or less reticulated substance, 
the structure of which is much like that of the cytoplasm of the cells 
(Figs, i, 2, 3, 4, 5, PL I). If it were not for the presence of the prochromo- 
somes it would often be difficult to distinguish between the structure of 
this framework in the nucleus and that of the cytoplasm (Fig. 4, PI. I). 
The substance of this framework is never impregnated with stainable 
chromatin. Through this reticulated framework run coarser threads, in 
which the chromatin is aggregated into the prochromosomes. The substance 
of the framework and of the coarser threads may perhaps be linin. I have 
been unable to discover any evidence that the threads of the framework and 
the threads which contain the prochromosomes anastomose. They are 
certainly different in staining reaction. The framework stains yellow with 
the triple combination, while the fibres which contain the prochromosomes 
stain blue with Gentian violet. In all nuclei at this stage, the prochromo- 
somes show as distinct, rather uniform bodies, arranged in pairs. They stain 
densely black with haematoxylin, and red with safranin. This pre-synaptic 
pairing in the germ cells must not be confounded with the paired condition 
which I have already described for somatic cells. There can be no doubt 
that the prochromosomes are paired in somatic cells. Although this con- 
dition is somewhat more difficult to observe in somatic cells, some of the 
prochromosomes are always to be found in pairs (Fig. 1, PL I). In my 
former paper ( J 05) I figured these prochromosomes in pairs in certain cases 
(PL VI, Figs. 1, 2, 3, 4, and 24) in somatic cells, although no emphasis 
