1 78 Farmer and Dig by. — Studies in Apospory and 
It may here be stated that we have investigated the prothallium of the 
common Male Fern, but have seen no cases of nuclear migration, nor have 
we been able to find any evidence of such migration in the case of the 
aposporously produced prothallia described below. 
We find that the number of chromosomes at meiosis (e.g. the heterotype 
mitosis) in this Fern is somewhat less than that characteristic of the 
common Male Fern at the corresponding stage. For whereas in the latter 
it is about 72, in the variety polydactyla of Wills it is about 64-66 (Figs. 39, 
40). The development of the embryo calls for no special remark. It 
is differentiated from the tissue of a prothallial excrescence, and we have 
nothing essential to add to the descriptions given by other authors. We 
have, however, given a few Figs. (54-56) to illustrate the process. It will 
be seen that it conforms very closely with the mode of development as 
it occurs in Pteris cretica } and except for the presence of archegonia, 
with that of Lastrea pseudo-mas var. polydactyla, Dadds. 
Comparing the size of the cells and nuclei of the prothallium with 
those of the typical form of the species, they are in both cases distinctly 
smaller, but there is not a consistent ratio between cell and nucleus. We 
find, as the result of a considerable series of comparisons of tracings made 
by the camera lucida of the cell network and nuclei of this variety and the 
type, that the average size of the cells is about 85 per cent., and of the 
nuclei about 60 per cent, of those of the common Male Fern. While we 
have taken all the care we could to make comparisons between prothallia 
that corresponded in age and development, it must be said that the 
measurements in any given single instance may show somewhat wide 
divergence from the mean or average. But nevertheless these numbers 
do convey very fairly the general impression gained as the result of 
comparing a considerable number of prothallia of the two Ferns. 
6. Lastrea pseudo-mas var. polydactyla, Dadds. 
The general habit of this Fern resembles that of the variety polydactyla of 
Wills, but it differs from the latter in many important points of development. 
The spores are fertile, and large quantities of prothallia have been 
raised from them. The young plants are all produced apogamously, and 
those which we allowed to continue growing have retained the characters 
of the parent plant. We have studied the development of the archesporium 
in order to ascertain the number of chromosomes in the sporophyte. They 
are very numerous, and an accurate estimation, as in the preceding variety, 
could not be arrived at (Fig. 57). When the spore-mother-cells are formed 
the divisions are of the meiotic type, the first being typically heterotype 
and the second homotype. It is not necessary to enter into details of these 
1 Cf. De Bary, Bot. Zeit. 1878. 
