Fertilisation , Apogamy and Parthenogenesis. 153 
in-breeding, unless there are special means, as in the Sperma- 
phyta, of bringing the two plants into relation 1 . 
The relationship between the nuclei which unite in Basid iobolus 
is very close; according to the latest researches of Woycicki 2 the 
nuclei of neighbouring cells unite after they have undergone two 
divisions. In the aecidium of Pliragmidium, 3 however (and probably 
also in other forms) a further stage of reduction is to be observed, 
for there the female cell, which is differentiated and has a sterile cell 
above, is fertilised by the entrance of the nucleus of a neighbouring, 
undifferentiated cell which passes through the wall, the two nuclei 
which become associated in the female cell being sometimes of such 
■close relation that they separated in descent merely by a single 
division (loc. cit., figs. 68 and 69). That this process is reduced in 
evolution is clearly shown by the presence of abortive spermatia 
which have all the characters of male cells. 
A still further stage of reduction of the process of fertilisation 
is to be seen in the case of “apogamy” in Ferns investigated by 
Farmer, Moore and Digby, 4 who found the nucleus of one vegetative 
prothallial cell migrating into another cell and fusing with the nucleus 
■of the latter, thus bringing about the doubling of the number of 
chromosomes. The term apogamy was invented by De Bary to apply 
to all cases in which fertilisation appeared to be absent and would 
include cases of parthenogenesis ; it has of late years been confined 
to those cases of transition from the gametophyte to the sporophyte 
without an obvious sexual process. It is evident how unsatisfactory 
is such a term when applied to a case which it is necessary to con¬ 
sidered as the union of closely related and undifferentiated gametes, 
since it can be linked on to normal fertilization through such a 
process as that observed in the aecidium, where the female cell is 
differentiated, though the acting male cell is undifferentiated. It 
would seem best to speak of both these processes as reduced forms 
of fertilisation, for they are clearly reduced both physiologically 
{in the close relationship of the fusing nuclei) and in descent. 
1 This does not seem to be always the case, for Blakeslee (Science 
XIX. (1904), p. 864, has lately made the interesting announce¬ 
ment that in some species of Mucor (“ heterothallic ” forms) 
there are two “strains” of mycelium, and that zygospores 
are only produced when hyphae from mycelia of the two 
“ strains ” come in contact. There is thus a differentiation 
of the nature of sex ; and the well-known difficulty of pro¬ 
ducing zygospores in some forms is explained. 
2 Flora, XCIII. (1004), p. 87. 
3 V. H. Blackman. Annals of Botany, XVIII. (1904), p. 323. 
4 Proc. Roy. Soc., LXXI. (1903), p. 453. 
