Oct., 1923] 
DARLING — CHROMOSOME BEHAVIOR IN ACER 
455 
stain with the gentian-violet. These free buds disappear as development 
proceeds. As to the significance of this behavior there is no direct evidence; 
it may possibly be an early fragmentation of the nucleolus, or it may be 
associated with chromatin anabolism; the latter is perhaps the more probable 
in view of the subsequent close association of nucleolus and chromatin in the 
late prophase stages of the mother cell. 
The significance of the synapsis stage is a topic that has been frequently 
discussed; many students of the cell have considered it to be the time of 
pairing of the paternal and maternal elements. Overton, however, says 
that in the plants with which he worked the prochromosomes are already 
paired at the stages of greatest chromatic distribution of the mother cell, 
and that the pairing may possibly occur in the telophases of the last pre- 
meiotic division. In these cases the individuals of a pair are very closely 
associated, in fact, so much so that in his earlier work the author considered 
each pair a single body. In Acer platanoides there may be a general group¬ 
ing of the chromatin bodies into pairs even in the resting stages of the 
nucleus, but their close association does not take place until synapsis. This 
evidence is in accord with the belief that synapsis is a significant stage in the 
heterotypic division. 
The manner in which the members of a pair of the chromatin bodies 
become joined together is shown to be an end-to-end arrangement; this 
fact is verified by the stages immediately following their union when the 
chromatin threads are formed by the flowing out of the chromatin in opposite 
directions from the paired chromatin bodies. There certainly is no evidence 
that I can find to support Cardiff’s more or less diagrammatic figures of a 
side-by-side pairing before synapsis; his figures 5 to 13, inclusive, which he 
interprets as pre-synaptic, are more suggestive of post-synaptic stages; he 
calls attention to the fact that the threads are arranged in pairs and that 
most of the pairs seem to be in contact with the nucleolus, or very near it; 
this is a condition which I find in post-synapsis. 
The interpretation of the nature of the pre-synaptic spirem has been 
the principal factor in the divergence of conclusions reached by the para- 
synaptic and telosynaptic schools. In forms like Acer platanoides and 
Acer negundo, as reported by Mottier, in which a pre-synaptic spirem does 
not occur, and in which the chromatin bodies are not split, this factor of 
whether the spirem is split or double is removed and the evidence for the 
manner of pairing becomes more conclusive. 
The chromatic spirem in Acer platanoides is formed during the synaptic 
contraction by the flowing out of the chromatin-staining material along the 
linin in much the same manner as found by Overton in Thalictrum. Mottier 
apparently did not determine the behavior of the chromatin masses in 
Acer negundo during the synaptic stages, but he states that the spirem is 
formed during this stage. 
The formation of the bivalent chromosomes from the thick chromatin 
