292 Peirce— On the Structure of the Haustoria 
to add, to the facts now set forth, observations on other species 
of Cuscuta collected and ‘ fixed ’ at different times during 
summer and autumn. 
Cuscuta Americana, L. 
Cuscuta americana , L. finds its nourishment on a variety of 
herbaceous and woody plants growing in the West India and 
Bahama Islands. The host-plants at my disposal were two 
species of Mimoseae, one of Apocynaceae, and Thevetia nerii - 
folia , J uss. I regret that the species of only one of these was 
determined, or is determinable. The structural differences 
between the hosts induce certain interesting differences in the 
growth of the haustoria, as will be shown further on. The 
parasite displays a remarkable difference in size between 
those parts which apply themselves to a host and those which 
are far removed from the sources of food. Thus, the average 
diameter of a well-nourished plant, in a region whence 
numerous haustoria penetrate a host, is 2-3 millimeters, while 
the average diameter of parts several centimeters distant 
from active haustoria is only 1 millimeter or less. I do not 
venture to say positively, owing to the incompleteness of the 
material at hand, that when two or more stems twine about 
one another instead of about a host, haustoria are never 
developed ; yet in one case observed, where three stems 
twined together for a distance of several centimeters, no 
haustoria were developed. If, however, one stem touches 
a host and sends haustoria into it, those which are twining 
with it quickly develop haustoria which, if not able to reach 
the host, strike into that stem which is being nourished as 
well as mechanically supported by the foster-plant. If, then, 
such be the general rule, it is evident that not contact merely 
is sufficient to induce the development of haustoria. 
When a Cuscuta - stem passes from one part of the host to 
another part, in such fashion that some haustoria if they 
develop far must strike only into the air (as when the parasite 
grows directly across from a branch to a leaf, or vice versa), 
these haustoria, having nearly reached the surface of the 
