86 BOTANICAL GAZETTE | aucust 
of one of the tetrad nuclei, more probably the smallest one 
The fact that several, perhaps the normal number of chromosomes 
are present opposes the view that it arose from an isolated 
chromosome. Six nuclei are found in fig. 26, the origin of 
four being shown by spindles. The two extra nuclei are quite 
small, containing but little chromatin, and may have been pto- 
duced by isolated chromosomes as above described. However. 
they were produced in this manner the smallest of the fou 
nuclei must have arisen by pathological mitosis by an unequal 
distribution of chromatin, for it is very small and contains but 
little chromatin. Figs. 27 and 28 show tetrads with supernumer 
ary cells. The cells of such tetrads are seldom of equal sid 
one or more of the cells usually containing a small nucleus. 
THE DEVELOPMENT OF THE MALE GAMETOPHYTE. 
The microspores soon after their separation and rounding of 
acquire the general shape and characteristic markings of the 
mature pollen grain, gradually becoming very much enlarged. 
(figs. 28, 30). A single elongated nucleus, which seems to have 
a small amount of chromatin, is found in the center of the spot 
until growth is far advanced - after which the division into genera 
tive and tube nuclei occurs (fig. 30). Until recently it ee 
thought that the tube nucleus never divides, but Chamberlait 
found many cases of such division in Lilium tigrinum and L. i : 
tum. Smith® found the same thing to be of frequent occurrent | 
in Eichhornia crassipes. emerocallis also shows this peculiatt) 
(figs. 31-35), many pollen grains having two, and a few havilg 
three, four, or even six tube nuclei. These were formed ?) : 
direct division in all the cases that I observed, as were ae 
reported by Chamberlain. Fig. 33 shows a very irregulat : 
nucleus, 
If the tube nucleus is the homologue of the cover cell of 
antheridium of. Marsilia, and represents the wall of an anther 
ium, it might sometimes divide through reversion to its se : 
7 Bor. Gaz. 23 > 423-430. 1897. 
* Bot. Gaz. 25: 324-337. 1898. 
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