IIo BOTANICAL GAZETTE | FEBRUARY 
and their apparently greater uniformity is probably due to their 
having been less fully investigated. 
S. perfoliatum presents a type of sac quite different from the 
other species studied (fig. 45). In size it agrees quite closely 
with S. ¢rifoliatum, these two species having larger sacs than the 
other three. The synergids are of a form peculiar to this 
species, and resemble more closely those figured for other Com- 
-positae. They are slender and pear-shaped, usually without 
vacuoles, and with the nucleus near the inner end. Their outer 
ends are long, and filled with a very deeply staining protoplasm. 
Their outline can be followed very easily inside the membrane 
of the sac, thus affording indirect evidence in confirmation of 
the claim that the cap found upon the tip of the sac in the other 
species is not a part of the synergids, but lies outside the sac. 
No attempt has been made to do cytological work in the 
embryo sac, as the difficulty of fixing the material quickly, due 
to the hard tissues of the ovary wall, rendered practically 
unavoidable an amount of shrinkage which, though slight, was 
sufficient to blur the finer cytological details. The yeneral 
appearance of the oosphere and primary endosperm nucleus has 
already been described. The drawings are not intended to do 
more than to show the structure of the nuclei more or less dia- 
grammatically. There is evidence that the egg nucleus leaves 
the resting condition before fusion with the male nucleus occul!s. 
The primary endosperm nucleus in S. integrifolium has an 
average diameter of 15 yw, its nucleolus being 6-8 » ; the oosphere. 
nucleus averages gu in diameter, with a nucleolus of 3m. The 
sac itself is about 220 by gow. In S. perfoliatum the endosperm 
nucleus measures 26m, its nucleolus 12; the egg nucleus 17» 
its nucleolus 6; the sac itself, about 300 by 65h. | 
DEVELOPMENT OF MICROSPORES. 
When the young stamen has reached the stage shown in fig: 
7, the hypodermal archesporial row is distinguishable from the 
surrounding tissue by the increased size of its component cells 
and their different staining reaction. A transverse section of 
