CHROMOSOME BEHAVIOR IN ACER PLATANOIDES L. 
Chester Arthur Darling 
(Received for publication December n, 1922) 
That chromosomes may be observed as definite bodies at nearly all 
stages in the life of a cell has been shown by various workers. Rosenberg 
(1904) and Overton (1905) were among the first to direct attention to the 
individual chromosomes in the resting nuclei in plant cells as definite 
chromatin bodies. In addition, Overton (1909) has figured these chromatin 
masses, “ prochromosomes ” as he termed them, in the various stages of the 
reduction division in the pollen mother cells of Thalictrum, Calycanthus, 
and Richardia. He maintains that these prochromosomes are in pairs in 
the resting nucleus of the mother cell; that in synapsis a continuous bivalent 
spirem exists in which the paired prochromosomes are arranged side by side 
at more or less regular intervals, and that they remain thus associated in 
parallel pairs until they separate at metaphase. Evidently these observa¬ 
tions and conclusions of Overton are in support of the Gregoire school which 
maintains that there is a side-by-side pairing of the chromosomes in 
synapsis. 
Digby (1919) has brought forward some corroborative evidence in 
support of the view of Farmer and his followers that the splitting of the 
spirem preceding synapsis is the same as the splitting in the telophases of 
the sporogenous mitosis, and that there is an end-to-end pairing of the 
chromosomes in synapsis rather than a side-by-side pairing. The difference 
between these two views of how the chromosomes pair appears to be due 
largely to differences in interpretation of stages associated with synapsis. 
Evidence which has a direct bearing upon this problem has been found in 
the study of the heterotypic division of the pollen mother cells of the Norway 
maple, Acer platanoides] in this plant the behavior of the individual chromo¬ 
somes may be followed with considerable clearness through synapsis. 
Cardiff studied this species, but his findings differ in several particulars 
from those of the writer, so that a reconsideration of this form seems 
justified. 
Methods 
In the preparation of the material for this study, the flower buds of 
Acer platanoides were collected in the early spring when the buds first began 
to enlarge. After removing the scales, the buds were dipped in 50 percent 
alcohol and then fixed in either Flemming’s medium solution or in Bouin’s 
solution. Dipping in alcohol caused the flower cluster to sink at once when 
placed in the fixing fluid and resulted in more uniform fixation of the 
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