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Gates and Rees. — A Cytological Study of 
presence in other mitoses of a connecting thread between the chromosomes 
which coalesce in the heterotypic mitosis. 
A similar situation exists as regards Vicia Faba. Here Fraser and 
Snell ( 1911 ) counted fourteen chromosomes in the sporophyte, and described 
in some of the chromosomes constrictions which they regarded as somewhat 
irregular in character. From the work of Sakamura ( 1920 ) it appears that 
one of these constrictions is constantly present in one pair of chromosomes. 
He figures (Fig. 16) only six bivalents on the heterotypic spindle and 
concludes that the number of chromosomes should be reckoned as twelve. 
But Fraser ( 1914 ) figures seven bivalents at this time, although two of them 
appear to be closely in contact. It therefore appears that, as in Lactuca , 
there may be failure of coalescence at this time. Probably the real number 
here should be considered as twelve, since the large M-chromosome pair 
shows a median as well as a subterminal constriction. Sakamura (p. 15) 
finds both these constrictions present in 92 per cent, of cases, but his figures 
of this and other species of jficia (in some of which he finds twelve and in 
some fourteen chromosomes) indicate that there is undoubtedly a considerable 
amount of variation in these constrictions. Again, Fraser and Snell ( 1911 ), 
although they state that seven is the gametophyte number of chromosomes 
in V. Faba> clearly figure six chromosomes in two cases (Figs. 26 and 28) 
in the first mitosis within the pollen grain, and doubtfully seven in one 
figure (Fig. 27) of the same mitosis. 
These constrictions in Vicia and in various other forms (the literature 
is reviewed by Sakamura) are of a somewhat different nature from the 
coalescences here described in Lactuca. For in the latter there is no 
indication of connexions in somatic mitoses or heterotypic prophase between 
the chromosomes which fuse on the heterotypic spindle. The constrictions 
therefore appear to represent incomplete separation of elements which 
belong to one chromosome, while the coalescences in Najas and Lactuca 
are the coming together temporarily of separate chromosomes. These two 
series of phenomena are undoubtedly closely .related, and Galtonia appears 
to represent a condition intermediate between them. The forms might be 
arranged in a series, Vicia , Galtonia , Najas , Lactuca , with incomplete 
separation of the parts of a chromosome on the one hand and only temporary 
coalescence of independent chromosomes on the other. 
A phenomenon closely related to the coalescence of bivalent chromo- 
somes in Lactuca has been described by Kuwada ( 1919 ) in Zea Mays , in 
which the chromosomes are slightly graduated in size. He finds that in 
starchy varieties of maize the diploid number of chromosomes is twenty, 
while in certain races of sugar maize the number varies in different 
individual's. Studies of root-tips in these plants showed 20, 21, or 22, and 
sometimes 23 or 24. The number of bivalents in the heterotypic mitosis 
in these forms was 10, 11, or 12. This increase in number is believed to be 
