1913] YORK—DEN DROPHTHORA 99 
17,18). Asimilar though somewhat more marked lobing occurs in 
Loranthus sphaerocarpus (TREUB 33). The epidermal cells imme- 
diately above the sporogenous cells divide by one or two peri- 
clinal walls, forming a small cap of cells which is probably to be 
regarded as the remnant of an integument (fig. 18). WARMING 
(38), in studying the development of the reproductive organs of 
Thesium, found that the contents of the epidermal cells above the 
apex of the nucellus were more densely granular than the remaining 
epidermal cells, and that the epidermal cells surrounding these 
granular ones divide by periclinal walls, forming a tissue about 
three cells in thickness, which he regarded as vestiges of integu- 
ments. 
The question of the interpretation of the elongated floral axis, 
the ““‘mamelon,’”’ has been a puzzling one. According to Hor- 
MEISTER, who first worked out its development in Loranthus 
europaeus, it is a “‘naked ovule”’ in which there are several groups 
of archesporial cells present. BAILLon also gave the same inter- 
pretation to this body in Arceuthobium. Treus believed that 
the “‘mamelon” is a growth of the floral axis in which the separate 
nucelli represent rudiments of ovules. In reference to Hor- 
MEISTER’S idea, TREUB asserts that there is no reason to consider 
this hemispherical process as an ovule reduced to its nucellus. 
Nowhere are groups of embryo sac mother cells formed in the 
lateral part of a nucellus as would be the case in Loranthus if the 
“mamelon” be regarded-as an ovule. 
Aucune raison ne nous engage 4 considérer le processus hémisphérique 
comme un ovule réduit a son nucelle. Nulle part plusieurs groupes de 
cellules méres de sacs embryonnaires ne naissent dans les parties latérales d’un 
nucelle, comme cela serait le cas chez le Loranthus si le mammelon en litige 
méritait le rang d’ovule. 
Comparing the enlarged floral apex or “‘mamelon”’ as seen in 
the Loranthaceae with that in certain genera of the Santalaceae, 
we find a striking resemblance and further evidence for the correct- 
ness of TrEuB’s views. In the early development of the flower of 
Thesium divaricatum, there is a central elongation of the floral axis 
as in Dendrophthora opuntioides and D. gracile. This ‘““mamelon”’ 
elongates with the formation of the ovarian cavity and forms a 
