Physiology of the Genus Ctiscuta . 105 
of these two, when it is possible to estimate them in 
mechanical units, will be found surprisingly large when 
the delicacy of the plant developing them is taken into 
consideration. 
2,. Penetration by the chemical activity of the pre-haustorium . 
Von Mohl 1 noticed that when a Cuscuta had wound about 
a polished silver rod, the positions of the haustoria against 
this rod were indicated, after the plant had been untwined 
from the support, by spots of a glairy fluid or of a shiny dry 
deposit. This he believed to be a mucilaginous matter which 
the parasite exuded in order the better to fasten itself to the 
host. L. Koch 2 considers it to be a solvent which is secreted 
for the purpose of softening if not dissolving the opposing 
tissues of the host, but he gives no experimental proof of this 
hypothesis. There are in the host three sorts of matter which 
may be affected by the parasite : the cell-walls, composed of 
cellulose and more or less infiltrated matter ; the starch and 
other carbohydrates in solid form ; and the nitrogenous sub- 
stances. Though the haustorium may be able by mechanical 
pressure alone to penetrate the tissues and to bring its 
vascular elements into direct contact with the phloem and 
xylem of the host, yet it goes without saying that it would be 
greatly to the advantage of the parasite were it able to 
supplement physical force by chemical action, and thus not 
only to make penetration easier, but also to allow the cells of 
the haustorium to dissolve, and thus to bring into available 
form, the solid nutritive matters around them. I have demon- 
strated in the foregoing pages that both contact and nourish- 
ment are necessary to the full development of haustoria. 
I shall now describe certain experiments showing some of 
the ways in which this nourishment is obtained. 
Let a mixture of two parts plaster of Paris and one part 
of starch (I used the large-grained starches of potato and 
barley), very thoroughly stirred together, be wetted with 
1 Mohl, H. v., loc. cit. (cited by Koch on p. 55). 
2 Koch, L., loc. cit., 1880, pp. 56, 57. 
