328 BOTANICAL GAZETTE [NOVEMBER 
the large nucleolus form the staining contents of the large 
transparent nuclear vacuole—the synapsis stage of the nucleus 
(fig. 7). This stage of the nucleus was also observed in Asclepias 
Cornuti, A. phytolaccoides, A. verticillata, and Acerates longifolia. 
At the beginning of mitosis the nucleolus often separates into 
several smaller nucleoli. The chromatin in A. éuberosa breaks 
into five chromosomes which split longitudinally while scattered 
in the nuclear vacuole (fig. 6). They are very small when 
split, but become much larger as the nuclear wall and the 
nucleoli disappear (fig. 6). After the disappearance of the 
nucleoli they are short, thick, and much larger than those in the 
vegetative cells. The number of chromosomes in the spore 
mother cells is approximately half that in the vegetative cells 
(compare fig. 6 with figs. 8and g). The exact number in the 
vegetative cells I was unable to determine. This reduction of 
chromosomes occurs in the spore mother cells of other plants. 
The mitotic phenomena attending the division of the cells 
referred to as spore mother cells closely agree, then, with those 
in the spore mother cells of other plants, and do not agree with 
those in the vegetative cells. This is to me conclusive evidence 
of their spore mother cell nature. 
Closely following this division, often before the cross wall is 
distinguishable, comes the second, with smaller chromosomes, 
which results in a row of four daughter cells representing a 
tetrad ( fig. zo). 
Both the rapid succession of these divisions and the forma- 
tion of four and only four cells from a mother cell homologize 
well with tetrad formation. - Each mother cell divides; those at 
the pointed upper end of the sporangium slope outward and 
downward, as shown in fig. 5, thus permitting the division of all 
the cells without great difference in size. The lower end of the 
sporangium is rounded, and hence the cells there are not greatly 
modified. These divisions I have no doubt are the ones Stras- 
burger saw in A. Syriaca, and this creates a doubt in my mind 
whether the mother cells near the ends of the sporangia formed 
only two microspores, as the report would lead one to believe. 
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