97 
Physiology of the Genus Cuscuta. 
ordinarily secure the penetration of its haustoria into a host ; 
by mechanical pressure, or by chemical action, or by a com- 
bination of both. In my previous paper I expressed the 
opinion, based on the appearance of the excellent alcohol- 
material which I had examined, that the haustoria made their 
way by solution. I still believe this to be true, and I shall 
presently give some experimental evidence in favour of this 
view. I said nothing about pressure, for the evidences of 
pressure were very slight. The following experiments 
demonstrating that both solution and pressure accompany 
the intrusion of the haustoria into the host will show how 
necessary it was to supplement purely histological examina- 
tion by physiological experiment. The plants used in the 
experiments now to be described were either C . glome- 
rata or C. europaea , the plants of C. Epilinum by the time 
these experiments were begun having almost ceased to 
vegetate, developing only flowers and fruits. 
If a branch of C. glomerata of suitable age be brought into 
contact with such a plant as Zea Mais at a part small 
enough in diameter to allow the branch to make close coils 
about it, haustoria will be produced. The branch should not 
be placed against the stem, which is protected by a peripheral 
ring of hard sclerenchyma, but rather against the base of 
a leaf still wrapped around the young stem, the whole 
diameter of stem and enclosing leaf being not more than one 
centimetre. After the haustoria first formed have penetrated 
the leaf, the leaf and the attached parasite should be cut 
away. Selecting, by the aid of a hand-lens, a haustorium 
which has developed to the point of entering the leaf but has 
not yet done so, careful transverse sections of the leaf should 
be made at this point, passing through and including the 
parasite which is attached to, though it has not yet penetrated 
into, the host. (The method of attachment is discussed in 
division II. 2 of this paper.) Taking for examination the section 
through the centre of the haustorium, the structure of the leaf 
will be seen to be as follows (see PI. VIII, Fig. 4). The 
upper surface (the lower, c-d , in the figure), which so near the 
H 
