Physiology of the Germs Cuscuta. 67 
contact. Previous authors have pointed out, but without 
proving the fundamental fact of its irritability, that Cuscuta in 
its two modes of twining alternately resembles twining-stems 
and tendrils. It is generally admitted now, despite the efforts 
of Kohl 1 to prove the contrary, that climbing-plants climb by 
the combined action of nutation and geotropism, and that 
most climbing-plants are not irritable to contact. (. Lopho - 
spermum scandens is one of the exceptions, its stems being 
slightly and its petioles considerably irritable.) When irrita- 
tion is not produced, either through the absence of all contact 
with irritable parts, or through the contact of a non-irritant 
such as wet gelatine, the plant grows and climbs only as other 
climbers do, making long, steep turns about the support. 
Like tendrils, the stem is not sensitive in regions of no growth 
in length, or in regions and at times of most rapid growth, but 
is sensitive at times and in regions of moderate growth. 
It is known that in the case of tendrils the effect of contact 
is not immediate, nor is it necessary that the contact should 
be permanent to produce winding. If momentary contact be 
made with very sensitive tendrils, for example those of Passi- 
Jior a gracilis, Link, and Sicyos angulatus , L., decided bending 
toward the side on which the contact was made takes place 
More slowly, if the contact be not renewed, the tendril 
returns to its former position. The process of twining is 
therefore induced , a short period of contact inducing a com- 
paratively slight and temporary bend, a longer one having 
stronger and more permanent effects, till finally a point is 
reached when withdrawal of the irritant object causes no 
return to the primary position of the organ, the induction 
having produced permanent effects. With tendrils less sensi- 
tive than those just mentioned, such striking effects are not 
produced, yet the principle remains the same. Now experi- 
ment shows that when the contact of an irritant object with 
the irritable part of the stem of a Criscuta produces certain 
effects, these effects are not immediate but are induced ; that 
1 Kohl, F. G., Beitrag zur Kenntniss des Windens der Pflanzen. Pringsheim’s 
Jahrbiicher fur wissenschaftliche Botanik, Bd. XV. 1884, p. 327, &c. 
F 2 , 
