1 68 Farmer and Digby. — Studies in Apospory and 
prothallia, and these have again been used to provide a second generation. 
The plant has bred true with us, though Mr. Druery speaks of the progeny 
as being very inconstant. 
The prothallia are nearly all of the expanded type, but a few cases of 
‘ bulbous’ prothallia have occurred in the cultures. 
We have satisfied ourselves that, as in the preceding variety, there 
is no reduction of the chromosomes associated with any stage in the life- 
history of this Fern. The prothallial cells, and the antheridial cells up to 
the last division leading immediately to the formation of the spermatocytes, 
have been studied, but the number of the chromosomes remains unaltered 
(Fig. 26) and is identical with that obtained in the nuclei of the sporophyte 
(Fig. 27). The result of a large number of counts indicate that there are 
about eighty-four chromosomes. Of course, when they are so numerous, 
the numbers are not to be regarded as more than approximately correct ; 
repeated countings of the chromosomes of the same nucleus often yield 
slightly different results. The limits of error, however, become narrowed by 
practice. It is more difficult to feel sure of the results of comparing 
together the nuclei of diffeient varieties of this species of Athyrium . We 
have endeavoured to do this, and believe that there is a specific number for 
each variety. We find in practice that the number in the variety now 
under discussion is slightly inferior to that of var. clarissima, Jones (see 
p. 164), and somewhat more numerous than in the typical Athyrium Filix - 
foemina , in which they are about eighty. These numbers are obtained by 
averaging the results of reliable estimations, and they also coincide with the 
impression given by a close examination and comparison of the nuclei 
of the varieties in question. 
The prothallial nuclei also exhibit the same remarkable chromatin 
nucleoli (Fig. 25) that are so striking in var. clarissima , Jones, but they are 
not so prominent as in that variety. In fact, in this as in many other respects, 
Mr. Bolton’s Fern stands about midway between the type form and 
Col. Jones’s plant. 
The prothallia, as has been observed, are extremely fertile. They 
produce large crops of antheridia, especially on the smaller prothallia, 
whilst upon the cushions of the larger ones archegonia of perfectly normal 
appearance are formed. As an exceptional circumstance, both antheridia 
and archegonia may occur on the upper surface of the prothallium, but they 
are for the most part restricted to the lower surface. 
The antherozoids are not as large as those of the clarissima , Jones, 
and differ in no constant character from those of the typical plant. The 
archegonia are formed in the normal manner, and when the neck opens the 
antherozoids are chemiotactically attracted and crowd into it, a few often 
slipping down into the venter. But no act of fertilization occurs, although, 
as will be seen, the embryo originates from the oosphere itself. 
