Physiology of the Genus Cuscuta. 71 
alternately in one, then in the other direction, twining accord- 
ing to the varying direction of nutation. Such alternation 
I have not seen. There is the further possibility that in some 
the tendency to nutate in a given direction is weaker than in 
most plants, and that therefore the irritation need not be 
unusually strong to cause winding in the opposite direction. 
Koch says it is not common for such turnings to be made. 
A very large majority undoubtedly twine in the direction of 
nutation, in the reverse direction to the hands of a watch. 
There is no more reason, however, why some plants should 
not twine in the opposite direction constantly, or in both 
directions alternately, than that there should not be left- 
handed or ambidextrous men and women. 
I have said above that the object of the close turns is to 
produce and to maintain an intimate contact between the 
parasite and its host for the purpose of developing haustoria. 
I have shown too that the process of twining closely is one 
which is induced by contact, following it after a longer or 
shorter interval. It may now be asked if the formation of 
haustoria is also induced by contact-irritation, and will be 
continued even after the contact has ceased to exist ? To 
answer this question a number of experiments were under- 
taken. 
If a branch of Cuscuta be brought into contact with a host 
and, after having made two or two and a half close turns 
about it and being about to form more, be gently removed 
from it and held from below in the same general direction, the 
branch will, like a tendril, continue to twine for a while. 
During the time necessary for the formation of two turns 
about the host, the contact will have been so protracted as to 
ensure the permanence of at least the lower one of these 
turns, but the time is too short (being about ten hours for 
C. glomerata) for any external evidence of haustorial formation 
to become visible. In the course of the next twenty-four 
hours, the usual swellings on the concave side of the curved 
branch will become evident, and these will continue for some 
time to increase in size. They are produced by the formation 
