Apogamy in Ferns . j 6 5 
mitosis shows clearly that they are the chief sources of the chromatin, 
which at these periods of cellular activity becomes distributed in the thread. 
We have examined these nucleoli not only with stains, but also with other 
agents, e. g. pepsin, and this latter reagent indicates very clearly that they 
consist almost entirely of a substance unaffected by it. Incidentally, we 
may remark, that an acidulated solution of pepsin affords a valuable method 
which much facilitates the counting of chromosomes, as after such treatment 
they become much more distinct, owing to the removal of other proteid 
matter from the cell. 
The prothallia, which usually show the customary differentiation of 
cushion and wings, produce large quantities of antheridia, and also a good 
crop of archegonia. The development of these calls for no comment, as 
it is perfectly normal up to maturity. In the antheridia, the mother-cells 
of the antherozoids were examined in order to test the possibility of a re- 
duction occurring at this belated stage, but without any other result than 
to show conclusively that no reduction occurs. The antherozoids (which 
are of a larger size than those of the normal Ath. Filix-foemind) are 
vigorously motile, and exhibit chemiotactic response towards o-i °/ o 
malic acid. 
The archegonia, although they are normally formed, very speedily die. 
The nucleus of the oosphere sometimes fragments, but the whole central 
row of archegonial cells soon degenerates and assumes the familiar yellowish- 
brown colour so characteristic of archegonia that have failed to become 
fertilized. But although they are thus destined to abort, they nevertheless 
are able, at maturity, to exert an attractive influence upon the antherozoids. 
On prothallia of this expanded type we have very seldom met with 
young sporophytes, and for a long time these were completely absent from 
our cultures. This appeared to us surprising, as Mr. Druery informed us 
that he was able to raise them readily. However, we did obtain a few, 
and these were always on prothallia that possessed a well-developed 
cushion. They are produced upon the cushion, and the superficial cells 
take part in the formation of the embryo. The root is formed endogenously, 
and burrows out of the prothallial tissue. It is impossible to distinguish 
in these cases the limit between embryo and prothallium, the cells of one 
pass insensibly (so far as appearance goes) into those of the other, and 
indeed, but for the presence of numerous archegonia in the cushion, it 
would be difficult to be sure that it was of prothallial nature at all and did 
not belong to the embryo itself. The embryo is, however, readily dis- 
tinguished from one that has arisen (sexually or otherwise) from an oosphere 
by the absence of a foot. The transition from the tissues of one generation 
to those of the other is quite gradual, and the prothallium itself, as often 
happens in such cases, exhibits considerable tracheidal differentiation. 
B. 7 he Bulbous Prothallium. This type of prothallium seems to have 
