TO I 
Physiology of the Genus Cuscuta. 
erect is able to do this, especially when it is enclosed by the 
parasite wound tightly and many times about it, for it is not 
yielding enough. 
That the pressure exercised by the growing haustorium of 
C. glomerata is very considerable, though so completely 
masked by the yielding nature of the stems and petioles of 
the species of Impatiens upon which it is parasitic, may be 
readily demonstrated thus. Wind a sheet of tin-foil four or 
five centimetres long and only wide enough to meet, not to 
overlap, around a stem or erect branch of Impatiens of suitable 
size, fastening it by binding bast. Bring into contact with the 
stem thus enwrapped a healthy branch of the parasite. Close 
coils will be formed and haustoria will also be induced by the 
contact. Their formation and growth cause the usual swel- 
lings, and these press with constantly augmenting force 
against the tin-foil. Finally the foil is ruptured, tearing in 
irregular fashion, and thus allows (see Fig. 5) the epidermal 
cells covering the irregular protruding mass to come into 
contact with the host. The haustorium continues to grow 
and presently makes its way into the host. If the tin-foil be 
wound twice about the host, the haustoria fail to penetrate 
the foil, though making marked impressions in it ; and they 
become abortive just as when they are formed in consequence 
of contact with other innutritious supports such as glass or 
wood. The tin-foil used in this experiment was two-tenths 
of a millimetre in thickness and of good quality. Through it 
the host could exercise no chemical influence on the parasite, 
nor could the parasite excrete a solvent of the metal. Hence 
we see that very considerable pressure is exerted by the 
growing haustorium and the epidermal cells immediately 
overlying it, and that pressure alone is sufficient to accomplish 
penetration into the host. 
Such pressure is paralleled by that exercised by normal 
roots, whether they be lateral or main ones. Prunet 1 has 
again called attention to this in a paper on the penetra- 
1 Prunet, M. A., Sur la perforation des tubercules de Pomme de Terre par les 
rhizomes des Chiendents, Revue Generale de Botanique, III, 1891. 
