334 BOTANICAL GAZETTE [way 
BoveERI (1) answers this question. After each mitosis, the chro- 
mosomes, and also the nuclei and cytoplasm, must grow before 
they divide again. Otherwise they will all continue to diminish 
in size. In tissues whose cells are of approximately equal size, 
the chromosomes must grow to their original size after each mitosis. 
At the beginning of meiosis, the chromosomes undergo the usual 
growth, so that, although the individuals are separated into two 
groups in the heterotypic mitosis, they must still divide again 
immediately before they are in condition to undergo further growth. 
GREGOIRE (12, p. 383) therefore suggests that the heterotypic 
mitosis is a process of chromosome separation intercalated between 
the last and the next to the last division of the diploid generation. 
If the mere separation of the chromosomes whose ancestors 
have been in close association throughout the sporophyte is the 
function of meiosis, then the peculiarly characteristic phenomena 
of synapsis are without an explanation. In a paper on reduction 
in Oenothera (4), I referred to the size relationships of the cells and 
nuclei in the archesporium and the pollen mother cells. It was 
pointed out (p. 5) that the cells and nuclei of the sporogenous tissue 
continue to’ grow simultaneously from the size indicated by figs. 7 
and 2 to that indicated by fig. 4 of that paper. Then (p. 7) the 
pollen mother cells cease to grow, while their nuclei continue enlar- 
ging. This is shown by comparing figs. 4 and 13. During this later 
growth of the nuclei, synapsis occurs. In figs. 4-10 of the paper 
cited, the nuclei are all of similar size and are taken from presynap” 
tic cells in the condition shown by fig. 4. In all the later figures 
(12-32), which are during or after synapsis, the nucleus is seen to 
be conspicuously larger. A comparison of fig. 4 with figs. 12 and 
13 makes it evident that the synaptic “contraction” is partly only 
an appearance, due to the sudden growth of the nucleus, that 15; 
an increase in the amount of the karyolymph. Occasional threads 
remain attached to the nuclear membrane and are drawn out 
ward as the nucleus enlarges (cf. figs. 12 and 13). There is also 
some contraction, however, as shown by comparing the diameter 
of the reticular area in figs. 12 and 13 with that of the nucleus oe 2 
fig. 4. In fig. 15, which represents a typical “‘synaptic ball,” it 5 
also evident that the diameter of this ball is less than that of the 
