1 77 
Apogamy in Ferns . 
substance at its anterior end. After the nucleus has thus traversed the wall, 
the pore through which it has passed is sometimes difficult to identify, 
at other times, however, it remains as a well-marked hole. The nucleus 
then generally seeks the nucleus of the receptive cell, and the two lie closely 
appressed to each other, and finally they fuse (Figs. 48-51). 
There are several variations that may be exhibited during the process. 
Sometimes the two nuclei do not immediately fuse, and we have seen many 
such instances of two nuclei lying in one cell, more or less near together, 
whilst there is invariably a non-nucleated cell immediately adjacent, from 
which one of the pair has come. At other times the fusion is very rapid, 
and both nuclei seem attracted to each other. Such an example is shown 
in Fig. 48, where the fusion is seen to take place almost simultaneously 
with immigration. A few cases which are perhaps to be regarded as 
‘abnormalities ’ occur, in which a nucleus will pass entirely through the 
adjacent cell, apparently attracted by the nucleus of one situated beyond 
it (Fig. 53), and, again, a few instances have been seen in which there are 
three nuclei in one cell (Fig. 52). But in every single case the origin of the 
invading nucleus was betrayed by the empty cell which it had abandoned. 
We have been able to trace the stages of fusion and division of the nuclei 
in question in a practically unbroken sequence. 
The fusion assumes special importance when the chromosome contents 
of the nuclei come to be studied. We find in these prothallia that some 
of the dividing nuclei possess the same number of chromosomes as the 
dividing spore-mother-cells during meiosis, that is, they have the reduced 
number (Figs. 41, 42). In such nuclei we find 64 to 66 chromosomes. 
Of course there is a little variation in the actual numbers obtained, 
when dealing with chromosomes as numerous as these, but the latitude 
is not large. In other nuclei belonging to the cells of the same prothallium 
we find many more chromosomes. We are not able to state accurately 
what the actual numbers are, but they are certainly considerably over 100 
(Fig. 43). We may fairly look on these as formed in nuclei which have 
duplicated the gametophytic (postmeiotic) number of chromosomes by 
fusion. The cells of the apogamously produced embryos have been 
studied, with the result that in every case we find these young sporophytes 
are characterized by nuclei possessing the double complement (premeiotic) 
number of chromosomes (Fig. 44). It thus appears to be clear that the 
nuclear cycle is essentially that of an ordinary sexual plant ; that is, the 
sphorophytic premeiotic chromosomes are distributed at meiosis between 
the two pairs of spores which arise from the spore-mother-cell ; from the 
spores arise the prothallial cell generations with the postmeiotic (reduced) 
chromosomes. But whereas in a normal life-history the premeiotic number is 
restored by the act of fusion of the egg and sperm nuclei, in this prothallium the 
same end is attained by the fusion of the nuclei of adjacent prothallial cells. 
