344 BOTANICAL GAZETTE [MAY 
of cells are in process of division amitotically, and can be found in 
all stages. All the tapetal nuclei have now increased much in size, 
those of the young tapetal cells being 8# in diameter, and those of 
the later stage 15 to 20H. As the blocks of sporogenous cells con- 
tinue to be formed and more widely separated, the tapetum com- 
mences to grow rapidly. The number of nuclei increases greatly, 
as well as the volume of the cytoplasmic mass in which they float. 
This pushes inward between the blocks with quite a regular outline 
(fig. 6). At prophase of the first division of the mother-cell, a section 
of the sporangium shows that these tapetal plates have extended almost 
across the sporogenous mass between the first formed blocks, and have 
commenced to grow inward between the blocks of later formation 
(fig. 6). This rapid tapetal growth continues pushing thinner and 
thinner plates between the smaller blocks as they are formed (jigs. 
7,8, 9), making a network which finally invests the individual tetrads, 
or groups of two or four tetrads (fig. g); and at last the spores separate 
and float in this tapetal mass. The original thicker plates of tapetum 
may often be found after the spores are completely formed. 
As this excessive tapetal growth takes place, the cell walls of the 
original tapetum break down successively from the inner layers 
outward, until at metaphase of the mother-cell the walls of only the 
outermost layer of tapetal cells remain. By the time anaphase of 
second division (fig. 8) is reached, the last walls of the tapetal cells 
have entirely disappeared, and the inner cells of the sporangial wall 
begin to take on tapetal characters; especially is this true of the nuclei 
which resemble tapetal nuclei very closely (jig. 9). The cell walls, 
while they collapse, have not been found to disintegrate entirely, as 
in the case of the true tapetum. In fact, there is no reason why these 
inner layers of sporangial wall might not be called tapetum. 
Probably the most interesting feature of the development of the 
Botrychium sporangium is the unusual growth of the tapetum. 
before mentioned, it increases greatly in volume and in number of 
nuclei, yet not a wall is formed anywhere, though it was stained 
especially for walls. The nuclei are found in all stages of amitotic 
division (figs. 5, 8, 9), but no evidence of mitosis is found. They 
take stains strongly, are exceedingly large, as mentioned above, and 
have an unusually thick nuclear membrane. That the nucleus 
