420 Osterhout . — On the Life-History of 
which are not found on the male or female plants. They 
often reach a length of an inch and a half, and bristle out 
from the frond in all directions. These proliferations are 
found to originate from tetrasporangia, which germinate 
inside the frond, the whole contents of a sporangium taking 
part in the formation of each proliferation. The process 
begins with the division of all the spores by means of oblique 
walls which do not occur in regular succession (Fig. 7). For 
a time it is possible to see distinctly the four separate masses 
of cells which result from the process, but as the process 
continues the boundaries between the originally distinct 
masses become obliterated, and one finds only a mass of 
cells occupying the place of the sporangium and preserving 
its general outline (Fig. 8), but already encroaching decidedly 
on the surrounding cells, and also projecting from the frond. 
The mass grows most rapidly in that portion lying nearest 
the outside of the frond, from which it gradually grows out 
to form the proliferations just described. As it does so the 
cells of the tip begin to show a definite arrangement into 
a central filament, which bears numerous short appressed 
branching filaments (Fig. 9), the terminal cells of which 
form the exterior of the frond. In the meantime the cells 
at the base of the proliferation grow out into rhizoidal 
filaments (Fig. 9), which make their way between the cortical 
cells of the parent frond, and finally reach the elongated 
cells of the medulla and form secondary connexions with 
them. 
Some of the proliferations remain sterile, but in the majority 
of cases they bear reproductive organs often before they are 
more than a quarter of an inch in length. Antheridial pro- 
liferations are very common, while tetrasporic and cystocarpic 
ones are rather rare ; but the three kinds often occur growing 
side by side. 
The union of several spores to form a single individual 
is by no means an isolated phenomenon, though it cannot 
be said to be a common one. Proliferations resembling those 
of Rhabdonia occur on the tetrasporic plants of Cystoclonium , 
