184 Farmer and Digby . — Studies in Apospory and 
Just as the chromosomes of this variety are fewer than those of the 
other varieties of Lastrea examined by us, so also the sizes of the cells, 
nuclei, and antherozoids are smaller than the corresponding elements 
in them. It is difficult in this, as in other cases, to give exact measure- 
ments, but taking the value of the respective structures in the typical 
Lastrea pseudo-mas as 100, a series of careful comparisons gives for this 
variety the following results : — 
Prothallial cells, 60 ; nuclei of prothallial cells, 75 ; antherozoids, 90. 
General Discussion. 
A consideration of the structure of the so-called varieties of Lastrea 
and of Athyrium which have been described in this paper serves to show 
that with the variation in form other important characters are associated. 
These characters not only concern the peculiarities connected with the 
particular form of apospory or apogamy that may be exhibited by an 
individual variety, but they extend to minute details of cell structure. 
Thus the ‘ varieties’ of Athyrium show, though in various degrees, a con- 
stant difference in the nucleoli of their prothallia as compared with those of 
the type. They all possess numerous chromatin nucleoli, and these assume 
at times very remarkable shapes. Moreover, there is in this respect a fairly 
regular amount of deviation from the type which marks the individual 
variety and distinguishes it from the others. Whereas the prothallial 
nuclei of the ordinary Lady Fern, Athyrium Filix-foemina , possesses com- 
monly one or sometimes two nucleoli, those of the variety clarissima> 
Bolton, show a number of these bodies. 
The corresponding nuclei of var. clarissima , Jones, possess the same 
peculiar nucleoli, consisting chiefly of chromatin, but they are more abundant 
and often assume very curious forms, at times recalling those of heterotype 
chromosomes, with which, however, they have really nothing to do ; they are 
simply nucleoli of very unusual form, and when mitosis takes place the 
chromatin from them passes out into the linin threadwork of the nucleus. 
The nucleoli of the variety unco-glomeratum , again, are also numerous, but 
they lack the unusual appearance presented by those of the former species. 
Another series of constant differences, which are probably of greater interest, 
lie in the size of the cells and nuclei of the different varieties. In I^astrea 
these differences are somewhat irregular, but in Athyrium we find them 
arrayed in a series in an almost regular manner. We will consider the case 
of Athyrium first, and it will conduce to clearness if we record the gradations 
as we have observed them in a tabular form, premissing, however, that the 
numbers given are not intended to express more than the average results 
obtained after the study of a considerable mass of material. They may, 
however, be taken as expressing the proportionate size as given by a large 
number of camera lucida drawings made to scale from the cells, & c., of 
