1 66 Farmer and Dig by. — Studies in Apospory and 
been met with by Mr. Druery, although his description indicates that his 
bulbils were not exactly similar to those produced by our plant. Probably 
the difference may depend on conditions of cultivation, for this type only 
became relatively frequent in our cultures when they were made in a cool 
greenhouse. They occur mixed with the expanded prothallia, and might 
be taken for vegetatively produced bulbils were it not for the fact that 
they frequently bear archegonia and antheridia. (The antheridia are, 
however, chiefly^ confined to such prothallia as occur along with them.) 
The bulbous prothallia recall the massive structures described by Bower in 
Polystichum angidare var. pulcherrimum , Padley, as one of the forms of 
prothallium produced aposporously on the leaves of that plant. They may 
be perhaps compared to the ordinary prothallia, by supposing that these 
had not developed wings, but had concentrated all growth upon the cushion. 
Probably the almost complete restriction of the embryo to the bulbous 
prothallium may be associated with storage of food. 
It is often very difficult to make out the manner in which the embryo 
develops from these bulbils, but comparison of a very large series shows 
that the young sporophyte is differentiated gradually, so to speak, from the 
apex of the bulbil, and usually involves a larger or smaller number of the 
internal cells. Sometimes it is only the terminal cells of the bulbil that 
give rise to the young plantlet (Fig. 19), but oftener those of an axile strand 
are also concerned. The first leaf always appears as a direct outgrowth 
from the apical surface of the bulbil (Fig. 18), whilst the first root is 
formed endogenously. In some cases, especially when the bulbil has reached 
a relatively considerable size, the whole of the interior cells are modified to 
form vascular elements — tracheids and sieve-tubes- — and a first impression 
is easily formed that the bulbil as a whole is really nothing but a vegetative 
sporophytic outgrowth from the parent leaf (Fig. 18). That this is not the 
case is always shown by more careful examination. The tissue connecting 
the bulbil with the leaf of the parent frond can invariably be made out to be 
prothallial in character, and this is further proved in the numerous instances 
in which archegonia, and sometimes also antheridia, have been found on 
its surface. 
Of course the real nature of the bulbil is very important to determine, 
and we took every care to verify our conclusions as to this point, not only 
by microtome sections, but by examining entire bulbils after suitable 
staining and clearing. 
The first stages of embryo formation (Fig. 19) are not easy to recognize, 
but they are betrayed by the existence of a little cap of whitish tissue 
situated on the somewhat broad free end of the bulbil. 
Sometimes the embryo development begins very early in the history 
of the bulbil, and these cases have all been carefully examined, lest we 
might have been deceived by an example of vegetative sporophytic budding. 
