1914] ELKINS—MATURATION IN SMILAX 47 
In plants which do not possess the persistent chromosome, the 
chance of observing the paired arrangement of smaller groups of 
chromatic units is much lessened. As mentioned early in this 
paper, the chromomeres or chromomere aggregates in either 
somatic or germ nuclei of Smilax herbacea frequently appear in 
pairs or double pairs. This seems to occur too often to be merely 
a coincidence, yet it could not be determined as a universal condi- 
tion. 
THE SEX DETERMINANT IN PLANTS.—Although no reference to 
the sex determinant has been made in the preceding pages, this 
study was first attempted with the hope of finding the idiochromo- 
some in a dioecious plant. Wutson (44), in his studies of the 
determination of sex in insects, places the decisive sex factor in 
the sperm. Here he found one-half of the sperms each carrying 
one or more extra chromosomes or a chromosome unique in size. 
All cases which cannot be placed in the above groups he relegates 
to a group where there is no physical variation of the chromosomes 
in the sperm cells, but where one may presume a physiological 
variation. 
Botanists have been unsuccessful in their efforts to find the 
idiochromosome. Darwinc (7) in working on the sexual cells 
of Acer Negundo (staminate material) found that one daughter 
nucleus after the first division contained a secondary chromatin 
mass; after the second division, two of the granddaughter nuclei 
each contained one more chromatin mass than the other two. 
In the resting stage, however, all the nuclei looked alike. To these 
secondary masses DARLING attached a possible sexual significance. 
Miss Sykes (42) found the nuclei of both sexes of unisexual plants 
She had studied (Hydrocharis Morsus-ranae, Bryonia dioica, 
Lychnis dioica, Mercurialis perennis, Sagittaria montevidensts, 
Cucurbita Pepo) to be identical in the number and form of the chro- 
mosomes. STRASBURGER’S (41) efforts to find a structural basis 
for the determination of sex were rewarded with negative results. 
On the nuclear reduction plate of Melandryum rubrum he observed 
a pair of chromosomes much larger than the other gemini; this 
same condition appeared again on the homotypic spindle. Thus, — 
one large chromosome was distributed to each of the tetraspores. 
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