BULLETIN 
TORREY BOTANICAL CLUB. 
Chromatin-reduction and Tetrad-formation in Pteridophytes. 
By Gary N, CALKINS. 
(PLATES 295, 296.) 
From the time when Van Beneden, in 1883, found that mature 
reproductive cells have only half as many chromosomes as the 
. Ordinary somatic cells, until the present time, cytologists have 
endeavored to explain the meaning of this reduction and to show 
how it takes place. These efforts have not as yet been attended 
with complete success. 
One of the most widely known theories as to the meaning of 
reduction is that of Weismann who accepted the earlier concep- 
tion of Roux (1883) as to the significance of mitosis and built 
upon it an elaborate theory of development. In this he predicted 
that a form of mitosis would be found in the maturation of the 
reproductive elements “in which the primary equatorial loops 
are not split longitudinally” (p. 371) and “by means of which 
each daughter nucleus receives only half the number of ancestral 
germ-plasms possessed by the mother nucleus” (p. 375). 
Weismann’s prediction has been confirmed by recent observa- 
tions on the copepod crustacea, and it is now known that in this 
group of animals at least, the chromosomes of a maturing cell un- 
dergo a transverse division, giving reduction in the Weismann 
sense. This process of reduction, wherever definitely made out, 
is invariably preceded by an arrangement of the chromatin into 
four-parted chromosomes, to which the name “ Vierergruppen” or 
“tetrads”’ has been given. These tetrads are always half as nu- 
