; 
1905] SHOEMAKER—HAMAMELIS VIRGINIANA 253 
the formation of cell walls, and the tapetal cells have two or three 
nuclei each; the nucleoli also increase notably, and the contents of 
the cell become more largely vacuolate (fig. 3). The pollen mother- 
cells thicken their walls, and soon float freely in the cavity of the 
anther ; increasing further in size, with a much larger nucleus 
and nucleolus (fig. 29). The two tetrad divisions occur almost 
simultaneously, although stages are found showing two nuclei 
(fig. 30). In the tetrad division the nuclear processes do not show 
at all clearly, though there seem to be fibers connecting the nuclei in 
one stage observed (fig. 31). The pollen grains have cell walls and 
but one nucleus when the mother-cell wall is broken down (fig. 32) 
and the grains released into the cavity of the microsporangium. The 
mature grain was described by Von Mout, very briefly, in 1835. It 
has the shape of an oblate spheroid, with three meridional furrows 
(fig. 33) ; between these furrows the surface is covered by a fine 
reticulation. An equatorial section shows that the intine is strongly 
developed under the furrows, which gives the section of the interior 
a decidedly three-lobed appearance (figs. 33 and 34). 
Soon after the pollen grain is freed from the mother-cell, its nucleus 
divides, and the smaller nucleus, probably the generative, retires into 
the extremity of one of the lobes. Here it becomes closely applied 
to the intine and is cut off from the larger cell by a very noticeable 
wall, which is probably of cellulose (fig. 33). Shortly before the pollen 
is shed this wall disappears, and the two nuclei then lie free in the 
Cavity of the grain. The larger of the two, the tube nucleus, is loosely 
vesicular, while the structure of the generative nucleus is dense and 
deeply Staining (fig. 34). ; 
Of the four layers in the microsporangium wall only the subepider- 
mal layer has any part in the opening of the anther, becoming the 
fibrous layer and covering the inner and lateral faces of the anther 
(figs. 5 and 6). The first and for a long time the only evidence of the 
differentiation of this layer is the radial lengthening of the cells. At 
this stage it is possibly not inappropriate to mention an instance of 
tegeneration observed in this fibrous layer. From some unknown 
Cause, the first subepidermal layer had been destroyed over a small 
area. The remaining part of that layer had developed normally. 
Into this gap tissue had grown from both sides, but that which came 
