12 1 
Acer negundo , L., and Staphylea trifolia , L. 
spireme is formed previous to synapsis ; that there is no union of two 
spiremes either before, during, or after synapsis, and that the spireme is 
composed of the somatic chromosomes placed end to end. In Acer 
negundo a longitudinal fission is not observed with certainty. The writer 
is unable to accept the origin of the bivalents as described by Darling- 
floe. cit., pp. 185, 186), who asserts that eight chromosomes come from the 
spireme, while five bud off bodily and full fledged from the nucleolus. As 
stated in a foregoing paragraph, Darling claims that the spireme itself is 
derived from the nucleolus by portions of the same which bud off and 
diffuse out into the linin, thus forming the chromatin thread, and that later 
five other bivalents separate from the nucleus by direct budding. I have 
expressed the view in earlier publications that the nucleolus contributes 
material to the nourishment of the cell, and it is not denied that the chro- 
matin may receive some of this material, but I do not interpret the small 
bud-like protuberances of the nucleolus which are frequently observed in 
earlier and later stages of the first mitosis of Acer negundo , and in other 
species of Acer studied by myself, as representing the manner in which the 
nucleolus contributes material to the cell. In all stages up to that of the 
multipolar spindle, the nucleolus is present, and sometimes one or two 
smaller additional ones (Fig. it). Even after the segmentation of the 
spireme, when the full number of bivalents is present, and on into the multi- 
polar spindle, the nucleolus is still on hand, and it is about as large, or 
sometimes larger than at an earlier stage (Fig. 16, 19). During the 
formation of the spindle, however, the nucleolus fragments usually into 
smaller bodies, and finally all traces of nucleolar material disappears, save 
small extra-nuclear nucleoli, which may be seen distributed throughout the 
cytoplasm. In some cases, just prior to the appearance of the multipolar 
spindle complex, the nucleolus may be seen to form large bud-like pro- 
tuberances (Fig. 20 a), and this may be reasonably interpreted as the 
breaking up of the nucleolus. Previous to the formation of the spindle, one 
or more bivalent chromosomes are not infrequently found lying close to, or 
in contact with the nucleolus (Fig. 20$), but in no case have I found 
anything to lead me to believe that any chromosome is formed bodily from 
the nucleolus. 
The formation of the spindle . At the complete segmentation of the 
spireme into the chromosomes, the latter appear much larger than in 
succeeding stages. The halves of any given bivalent may be thicker than 
the spireme from which they have just been formed. This is doubtless due 
to a shortening which always follows soon after complete segmentation. The 
bivalents now become distributed throughout the nuclear cavity, where they 
are seen to be connected with each other and with the nuclear membrane 
by delicate threads. They now undergo the process of condensation by 
which their size is greatly reduced, and show a tendency to be distributed 
