204 BOTANICAL GAZETTE [SEPTEMBER 
dropemon parvifolius were placed in the dark chamber with those 
of Dendrophthora opuntioides and germinated as readily as those 
under normal conditions. Chlorophyll is not present in the endo- 
sperm of Dendropemon parvifolius, but is abundant in the embryo. 
From this fact it is seen that the endosperm in Dendrophthora and 
also in Phoradendron, which is quite similar, is also a carbon dioxide 
assimilating organ. It will be of interest to mention here that the 
radicles of the seedlings of Dendropemon parvifolius which ger- 
minated in darkness did not turn down toward the substratum, but 
grew out at various angles. Some, for example, extended upward 
at an angle of go’, while others were parallel to the substratum. 
Thus the bending of the radicles toward the substratum is not 
due to gravity or to attraction by the substratum, but their behavior 
seems to be a negative response to the stimulus of light. 
Dutrocuet (6) found that the “hypocotyls” of Viscum album 
are negatively heliotropic. His observations were later confirmed 
by WIESNER (39). The endosperm in its development, as seen in 
this study, may thus be regarded as being parasitic, drawing its 
nourishment through its outer layer of haustorial cells from the 
adjacent tissues. It also becomes a storage tissue, containing an 
abundance of food material for the embryo and a region in which 
photosynthesis occurs. 
The viscin 
Owing to the lack of fresh material at Baltimore, a detailed 
study of the viscin has not been possible. Its structure is essentially 
the same as described and figured by Jonnson in Arceuthobium 
Oxycedri, and by Perrrce in A. occidentale. Parallel with the 
maturation of the embryo sac, the cells in the outer half of the 
carpels become colorless and begin to enlarge (figs. 20, 56). Later 
they elongate obliquely toward the base of the style when the 
formation of the embryo begins. In the ripe berry they are greatly 
elongated and their walls consist. of two layers. The outer layer 
is composed of gelatinous material, while the inner is usually made 
up chiefly of spiral cellulose thickenings (fig. 57). As a rule the 
cell cavity is very narrow, and in some cases has been almost 
obliterated, the cell being chiefly composed of gelatinous material 
(figs. 58, 59). In some cells the outer wall is spirally thickened. 




