1913] YORK—DEN DROPHTHORA 211 
In these respects this process may be said to be like the usual type 
of fertilization. This conjugation of gametophytic nuclei in D. 
gracile may also in a sense be regarded as a sexual process, in that 
there is a gametophytic generation followed by a sporophytic in 
which the sexes are in different individuals. 
DeBary (5) was the first to use the term apogamy, restricting 
it to cases in which fertilization had disappeared; hence this 
interpretation does not apply in D. gracile. The union of the polar 
nuclei in this plant should be regarded as a substitution process or 
pseudo-fertilization, which in some respects is like a true fertiliza- 
tion. The body arising from the fusion nucleus represents a pro- 
embryo or pseudo-endosperm, and the embryo is regarded as 
pseudo-apogamous in origin, as in D. opuntioides. The term 
pseudo-apogamy is not used here in the sense in which it was used 
by FarMeER and Dicsy. In Lastrea pseudo-mas var. polydactyla 
Wills, there is a fusion of nuclei which the author believes is a sub- 
stituted form of fertilization quite like that in D. gracile. 
The presence of such a difference in the mode of origin of the 
proembryo in two closely related species as shown here is indeed a 
very striking phenomenon; perhaps, however, no more so than the 
two different modes of origin of the sporophyte in the varieties of 
Lastrea pseudo-mas already mentioned. This phenomenon may be 
due to the difference in the number of chromosomes present in the 
gametophytic cells. The fact that in one example development 
occurs without any sort of fertilization, while in the other it does 
not take place until the number of chromosomes is doubled, sup- 
ports the theory that a nucleus must have the sporophytic number 
of chromosomes for starting the sporophytic generation. YAma- 
NOUCHI’S account of the origin of a sporophyte whose cells contain 
the haploid number of chromosomes from a haploid gametophyte 
in Nephrodium is evidence against this hypothesis. One of the most 
important problems for solution is the determination of the factors 
which have led to this difference. Since we know comparatively 
little of the physiological relation of the Loranthaceae to their 
hosts, it is almost useless to attempt an explanation of this phenome- 
“Dass einer Species (oder Varietit) die sexuelle Zeugung verloren geht und 
donc einen andern Reproduktionsprozess ersetzt wird.”’ 
