( 
70 Peirce . — A Contribution to the 
selves necessary to the formation of haustoria. They are 
simply a means, and the easiest and most effective one, of 
bringing a considerable area of the stem or branch of the 
Cuscuta into intimate contact with the host, and of maintain- 
ing this contact. If intimate contact be formed and main- 
tained over a considerable area in any other way, which is 
rarely the case in nature, the haustoria will be formed without 
the usual preliminary of winding. 
It has been asserted by L. Koch 1 that the stems and 
branches of these parasites can, and sometimes do, twine 
closely about a host in the opposite direction to their nuta- 
tion, and then form haustoria as usual on the side in contact 
with the host. I have not had the good fortune to see such 
plants. Experiments show, however, that Cuscuta is not more 
irritable on one side than on another. In the experiment 
just described, where a branch was enclosed between two 
leaflets, the contact and pressure were alike on both sides. 
Haustoria were formed on both sides penetrating the two 
leaflets equally well, the haustoria generally alternating in 
sets of three on the two sides ; but some haustoria were 
directly opposite one another. 
If a young branch growing quite free be marked with 
a straight longitudinal series of dots for a distance of five 
centimetres from the tip, it will presently become evident 
that, both in free growth and in the formation of close turns 
after contact with a host, a decided torsion of the stem takes 
place, and that the line of haustorial development does not 
bear any definite relation to this line of dots. From the 
absence of bilaterality in the stem, there is no reason why, 
when the close turns have once been made in the direction 
opposite to the nutation, the haustoria should not develop. 
To overcome the tendency to nutate in one direction, and to 
bend sharply and for a time continuously in the opposite 
direction, might require very strong irritation ; or it might be 
that some plants of this genus (as in a few others 2 ) nutate 
1 Loc. cit., 1880, p. 18. 
2 Compare Darwin’s Climbing Plants, about Scyphanthus elegans , &c. 
