436 CANNON: GERMINATION OF PHORADENDRON 
parasite, but they, with lignified walls, unlike the latter whose walls 
were unmodified, were unaffected by this fluid. 
The question at once arises as to whether the seedlings of the 
mistletoe secrete enzymes which can dissolve suberized, cuticularized 
or lignified cell-walls, and thereby gain entrance into the host at 
nearly any point, or, as may be the case in the haustoria of mature 
plants, only unmodified walls are affected. Ofcourse it may be that 
cuticularized walls can be dissolved and neither of the other two. 
I have no evidence to offer in the latter alternative, but it is notice- 
able that the mistletoe is almost never parasitic on itself * in spite 
of the fact, which will be given later, that the seedlings often ger- 
minate in contact with its own branches. Dr. MacDougal informs 
me, however, that several instances have been known of the par- 
asitism of one loranth on another in Jamaica. The mistletoe is 
provided with a cuticularized epidermis with communication to the 
exterior through stomates only. 
In the vicinity of the Desert Botanical Laboratory occur two 
species of mistletoe, P. vi//osum and P. californicum. The former 
has white berries and broad leaves, the latter has red berries and 
is nearly devoid of leaves. P. villosum occurs here mainly on the 
native ash and native cottonwood and appears to be quite like the 
California plant studied by me. The other species has a different 
habit of growth. It generally hangs from the branches of the 
host, and is found mainly on the cat-claw (Acacia Greggit), and 
mesquite (Prosopis juliflora). 1 have seen it also on palo verde 
(Parkinsonia microphylla); and 1 believe that it occurs on the 
creosote bush (Covillea tridentata), but I have not seen it on this — 
plant. 
The distribution of the mistletoe from tree to tree is likely 
always effected by the agency of birds, but its distribution in a tree 
may be brought about in another manner also, and thus it is fre- 
quently accounted for by the position of the older plants. In 
cases where infection has occurred on the higher branches of 
the host it frequently happens that numerous younger plants of 
the parasite will be placed directly under this pioneer, as if they 
ee ee ol 
*In Kerner and Oliver’s work, /. ¢., it is said that on one occasion mistletoe, prob- 
ably Viscum, was seen growing on Loranthus. It, however, is not clear whether the 
place where the Viscum seedling gained an entrance was cuticularized or suberized. 
oS ee Ser lr seta a 
