CANNON: GERMINATION OF PHORADENDRON 439 
dermal wall is strongly cuticularized, and hence the hypocoty] is 
xerophytic. This not only ensures against rapid drying out but 
probably the converse of that, making impossible, perhaps, the 
absorption of water should it chance to come during the early 
stages of germination. 
The cotyledons probably never emerge from the seed until 
foothold has been secured by the root, and this may not take 
place under several months from the time germination commences ; 
they are thus unlike those of Loranthus, which appear much 
more quickly. * FicurRE 2 shows a young plant of P. villosum 
on a cottonwood branch. It was collected in January and the 
seed presumably was one that ripened and began to germinate 
the previous season. The seed-leaves, however, had not yet left 
the seed-coat ; they were closely pressed together like the young 
leaves in old plants. 
There are three well-marked periods in the life of the young 
mistletoe plant: 1, the growth of the hypocotyl and the formation 
of the disc ; 2, penetration; and 3 (probably after the establishment 
of a connection with a water supply), the erection of the cotyledons. 
Some very interesting work is to be done on the causes that 
influence the radicle to turn towards the host. In P. vd//osum this 
almost always occurs at once but in the other species the radicle 
may bend and twist in a variety of ways before the host is 
touched. However, in the end the tip of the radicle touches the 
substratum and flattens into a disc-shaped organ, likely as a result 
of the pressure caused by the resistance of the host. The young 
disc was not especially studied; it has been long known that it 
secretes a substance which aids the penetration of the haustorium. 
The discs increase in size by the multiplication of cells about the 
periphery, and in older forms, in which penetration has already 
taken place, secreting cells of the disc are confined to the outer 
portion (FIGURE 3). These are as usual elongated, they have 
dense protoplasmic content and conspicuous nuclei. 
Penetration is effected unlike in the two species, and in the 
instances cited, the manner of penetration is dependent on the 
* Keeble. Loranthaceae of Ceylon. Trans. Linn. Soc. London, II. 5: 91. 1895. 
t Compare the account given in Engler & Prantl, Nat. Pflanzenf. 3" : 160, and by 
Keeble, oc. cit, supra. 
