70 B Beer. — Studies in Spore Development. II. 
paired prochromosomes such as Lundegardh (15) has illustrated in his 
Fig. i, Tafel 2. My search has, however, always been in vain, and I have 
found no single instance in which the chromatic aggregates are regularly 
arranged in pairs as we see them in Lundegardh’s figure, or in which they 
show any fixed relation to the chromosome number of this plant. 1 I have 
found, on the other hand, that the structure of these nuclei conforms much 
more nearly to Davis’s account of the presynaptlc nuclei of certain Evening 
Primroses (1, 2, 3). Here he finds a number of chromatic bodies derived 
from the chromosomes of the last premeiotic division gradually merging 
their substance with that of the reticulum, from which they cannot finally be 
differentiated. This reticulum, without any apparent chromatic bodies upon 
it, passes into synapsis. 2 
In the Compositae the vacuolization and breaking up of the chromo- 
somes at the conclusion of the last premeiotic division are usually fairly 
complete, and by the time the prophases of the heterotype division are 
entered upon, any correspondence between the number of chromatic aggre- 
gates and that of the chromosomes of the last somatic division is quite lost. 
The small, irregular chromatic lumps and thickenings upon the reticulum 
during the early stages of the prophase of the division are, nevertheless, the 
last remains of the somatic chromosomes which have very nearly, but not 
quite, distributed their substance over the general reticulum of the nucleus. 
Before synapsis is entered upon there is usually a still further smoothing out 
of the reticulum, although there is some variation in the degree to which this 
progresses. Although, so far as the presynaptic pollen mother-cells of the 
Compositae 3 are concerned, I find definite prochromosomes or gamosomes 
to be non-existent, there is no reason to doubt that in the cells of other 
organisms the chromosomes of the preceding division may possess a more 
marked persistence, and remain as clearly recognizable bodies which occur 
in the same number as the chromosomes. We have an example of this in 
the meiotic cells of the testis of Tilton described by J. E. S. Moore and 
Miss Embleton 4 (17), 
Synapsis. 
The nucleus, containing this usually fine and smooth reticulum, next 
passes into synapsis. During this process there is an enlargement of the 
nuclear cavity, and the reticulum becomes gradually drawn together on one 
1 Lundegardh found the somatic chromosomes to number twenty-eight in this plant. 
2 Small, deeply staining bodies often occur in the nuclei of the vegetative cells and archesporial 
cells (previous to meiosis) of Calendula . These are sometimes single and sometimes paired. They 
are derived from the fragmentation and median vacuolization of the chromosomes of the preceding 
division. These bodies are, however, always absent from the nuclei of the pollen mother-cells 
shortly before synapsis (see PL LXVII, Fig. 77). 
3 i. e. those species which I have examined. 
4 Compare also the behaviour of the chromosomes of Matricaria during the interkinesis of the 
meiotic phase which is described below. 
