1918] WEIR—RAZOUMOFSKYA 9 
tions, depending upon the region where grown. The same varia- 
tion is noted in the robust form when grown in the North. This 
shows that these plants from the different localities cannot be held 
specifically distinct on a basis of color. Although color has been 
one of the chief distinctions between the two, the cultures show 
that there is no marked difference in the general morphology 
of each form when grown outside of its original place of collection. 
True, there are some differences to be noted with respect to size, 
but it is purely a matter of age of infection. Even after the 
first maturity these plants, which have a comparatively long life, 
grow larger by developing additional branches and increasing the 
thickness of the stem. The comparisons made. in the table are 
based on plants differing widely in age; consequently measurements 
must vary slightly. Excepting color changes, which were to be 
expected from varying habitats, the general morphology of the 
younger plants of the parent colonies were in no particular different 
from those of the cultures. The cultures have also demonstrated 
the fact that R. campylopoda will infect Abies, with considerable 
variation in color and size of the resultant plants, but closely 
resembling the form known as R. occidentalis abietina. It is inter- 
esting to note in this connection that CoviLtE‘ refers the plant 
found on Abies magnifica and A. concolor directly to R. campylopoda 
(R. occidentalis [Engelm.] Coville) with the statement that it is 
probably the plant that ENGELMANN’ had previously described 
under this name (Arceuthobium campylopodum). Itis further shown 
' that R. campylopoda will infect Picea and Larix, but with difficulty. 
This mistletoe also will apparently readily infect Pinus contorta, 
a result repeatedly confirmed in the field. This tree, however, is 
not a common host. As will be shown in the case of R. americana, 
it is believed that this parasite may be expected to occur on any 
hard or yellow pine, but with predilection for certain species. The 
mere assumption that hosts are the determining factors of a species 
is here shown to be untenable. When a parasitic species will infect 
hosts from widely separate regions and even genera, and the result- 
ing plants have certain characters varying from those exhibited 
4 Contrib. U.S. Nat. Herb. 4:192. 1893. 
5 Gray, AsA, PI. Lindh. 2:214. 1850. 
