6 4 
Peirce . — ^4 Contribution to the 
hours, make two or three short turns closely around the 
vertical rod. Within the next fifteen hours more such turns 
may be made, and it will be evident from the swellings on the 
side of the Cuscuta next to the support, that haustoria have 
begun to form. If the contact between the Cuscuta and the 
vertical rod be made at a point only about one centimetre 
from the tip of such a more slowly growing part, there will 
be little or no effect. If the point of contact be too far from 
the tip, more than six or seven centimetres for C. glomerata , 
there will also be little or no effect ; if far enough back, 
absolutely no effect. 
The parallel of such a condition of affairs is exactly 
furnished by tendrils, for example of Passijiora gracilis, Link. 
A wooden, metallic, or glass rod placed in contact with 
a young, short, and rapidly-growing tendril, whether the 
point of contact be near the tip or the base, or in the middle, 
will produce no effect. When, however, the tendril ceases to 
grow so rapidly, having attained a length of several centi- 
metres, on such a rod being brought into contact with it at 
a point about three centimetres from the tip and against the 
side toward the direction of nutation (the concave side), 
twining will take place. If the contact be made at or very 
near the tip, or in the region nearer the base which has ceased 
altogether to grow, there will be no effect. Every one knows 
that the tendrils are sensitive to irritation by contact, and it 
is the general opinion that the stem of Cuscuta is so also, but 
so far as I am aware no sufficient proof of this has yet been 
adduced, though since Von Mohl first made the statement in 
1837 many have studied the plants of this genus in various 
ways. In a very suggestive paper by Pfeffer 1 3 one finds an 
account of a series of interesting experiments on tendrils, in 
which it is clearly shown that fluids (unless they are poisonous 
or contain solid particles in suspension) produce no irritation 
by contact. Pfeffer found also that gelatine, if kept wet, also 
produced no irritation by contact, but, when allowed to dry, 
1 Pfeffer, W., Zur Kenntniss der Kontaktreize, Untersuch. aus dem Bot. Institut 
zu Tubingen, Bd. I, p. 483 et seq., 1885. 
