222 BOTANICAL GAZETTE [ SEPTEMBER 
familiar spirem stage is reached. The nucleus is smaller than the embryo 
sac nucleus of the same stage, but the ribbons have about the same width in 
both. “It seems probable that the linin matrix of the ribbon is formed in 
great part from the substance of the half dissolved nucleolus.” The double 
row of chromatin granules is first demonstrated with certainty during the 
ynapsis stage, but Miss Sargant believes that it occurs earlier. As in the 
embryo sac nucleus, longitudinal splitting of the spirem ribbon precedes the 
division into the segments which constitute the chromosomes. Each of these 
chromosomes thus consists of two distinct longitudinal segments which sepa- 
rate during karyokinesis. Each of these segments shows a double row of 
chromatin granules, thus suggesting a fourfold character of the chromosome 
and recalling the tetrad of the animal spermatocyte, which in Ascaris results 
rom a double longitudinal fission. A second fission could not be demonstrated 
either in the embryo sac or pollen mother cell of Lilium. Spindle fibers 
appear from two or three points in the cytoplasm, forming a spindle which is 
rarely symmetrical at first. Attached to each chromosome are two bundles 
daughter chromosomes in the diaster stage are commonly V-shape 
The number of chromosomes was twelve in all cases in which on could 
be counted with certainty. There is a suggestion that the daughter chromo- 
somes of the first division retain their identity within the daughter nucleus. 
The nucleus of the pollen grain divides once before the grain is shed, and 
he daughter chromosomes separat tly asin the vegetative nucleus. No 
centrosomes were observed, but there was often a differentiated mass of cyto- 
plasm from which radiations could be traced into the surrounding cytoplasm. 
The generative nucleus, which divides soon after the formation of the pollen 
tube, shows a definite longitudinal splitting of the chromosomes. The gen- 
erative nuclei are exactly alike and neither possesses a nuclear membrane OF 
a nucleolus. In the three later divisions the number of chromosomes could 
not be counted with certainty, but there were about twelve. 
In both spermatogenesis and oogensis the parent chromosome gives rise 
to daughter chromosomes by longitudinal fission. The seven divisions of these 
series are all distinguished by having twelve chromosomes instead of twenty- 
four. Of these seven divisions the first of each series differs decidedly from 
the rest, which are distinguished from the vegetative type only by the 
reduced number of chromosomes. ‘The name “homotype,” already in use by 
zoologists, has been given to the five divisions which follow the vegetative 
ype, while the term “heterotype” is applied to the first division in each 
series. In the spirem stage of the homotype division the ribbon stains 
uniformly, while in the corresponding stage of the heterotype the ribbon is 
bordered by a double row of cyanophilous granules. In the homotype 
division the chromosomes are formed of lengths of the spirem ribbon, the 
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