Physiology of the Genus Cuscuta. 85 
interior of the leaves. In Juncus and Equisetum the haustoria 
so rarely succeed in uniting with the vascular bundles that 
from these plants but a small amount of food can be 
obtained. 
The fact that, when occasion demands, the Cuscuta can 
develop a very considerable quantity of chlorophyll which, in 
the appearance of the plastids which contain it, in their 
position in the tissues, and in their abundance, justifies the 
belief that it is a highly functional element of the plant, is 
most interesting confirmation of the hypothesis that this 
genus of plants has become parasitic within comparatively 
recent times and after having attained a fairly complex 
development such as the other and non-parasitic members of 
the Convolvulaceae possess. I have as yet had no oppor- 
tunity of pursuing the interesting questions thus presented, 
but I hope to be able to do so later. 
3. General relations of Cuscuta to its environment . 
There remain to be discussed one or two general questions 
concerning the relations of Cuscuta to its environment, in view 
of the conditions necessary for the formation and development 
of haustoria, before I pass to a consideration of how the 
haustoria enter the tissues of the host, and attach themselves 
to the vascular bundles. 
As already pointed out, the roots of Cuscuta are very feebly 
geotropic organs. The stems, on the other hand, are strongly 
negatively geotropic ; for though they may be ready to make 
close turns about a support, provided the necessary conditions 
be complied with, yet if rough and thereby irritant rods of 
suitable size be held horizontally against them no twining will 
take place. The negative geotropism of the stems is stronger 
than their irritability. It is to be noticed, however, that when 
close twining has taken place around a vertical support, and 
haustoria have been induced by this means, changing the 
support to a horizontal position does not prevent the haustoria 
from forming, or delay them in their development. Geotro- 
