86 Peirce . — A Contribution to the 
pism prevents the formation of haustoria only in so far as it 
prevents the formation of the close spirals, on whose concave 
surfaces they are normally formed. The biological advantages 
to the plant in this arrangement are plain and important. 
Unless it is able to reach the top, or the periphery in general, 
of its more or less spreading host, its neither large nor con- 
spicuously coloured flowers will fail to attract the attention of 
those insects by whose visits they are cross-fertilized. Yet if, 
after having coiled about and having been stimulated to form 
haustoria against a nutritious support, the accidental bringing 
of this support to a horizontal position were to stop the 
formation and development of haustoria, much would be lost 
and nothing gained. For, by developing the haustoria already 
induced, the parasite can secure the food obtainable from an 
otherwise valueless host, and thus the sooner be in condition 
to seek a better support. 
It might be supposed that, if the effect of geotropism were 
neutralized by revolving both host and parasite horizontally 
by means of a clinostat, contact would then be sufficient to 
induce winding about a support placed in any direction. In 
order to determine whether such is the case or not, I put at 
different times on the clinostats of Pfeffer and of Wortmann 
healthy plants of C. Epilinum , C. europaea , and C glomerata , 
growing respectively on Liman , Chrysanthemum , and Im- 
patiens ( Sultani and parviflora :), which had been growing in 
pots in the greenhouse long enough to have become thoroughly 
acclimated, revolving them around a horizontal axis for periods 
varying from one to five days. In no case did twining take 
place, however carefully the contacts were maintained. The 
parasites grew in length in perfectly normal fashion. The 
absence of irritability to contact was the most noticeable 
difference from their usual state. Furthermore, a plant taken 
off the clinostat after having been revolved horizontally and 
continuously for two or three days around its long axis, was 
not at once sensitive to contact-irritation. The period of 
insensibility varies in proportion to the length of time the 
plant has been upon the clinostat. A plant of C. europaea 
