87 
Physiology of the Genus Cuscuta . 
which had been on the clinostat for seventy-two hours did 
not begin to form close spirals around a support until twenty- 
four hours after it had been restored to the vertical position ; 
then, however, it twined and developed haustoria in the 
usual time. 
If parasite and host be laid horizontally, the parasite will 
bend upwards as quickly and as sharply as the host, although 
at the time it may be in contact with a horizontal rod. 
As shown so clearly by Wortmann 1 , geotropism is such an 
important factor in the climbing-power of plants that we 
should not greatly wonder that Cnscuta did not wind about 
horizontal rods either when it was itself erect or horizontal ; for, 
from the fact that it is only at times that the parasite winds 
about its support in a way different from that of an unirritable 
climbing-plant, in other words is irritable only at times, we 
see how important and how constant the effect of geotropism 
on its growth must be. But it is surprising that the neutraliza- 
tion of geotropism by revolving the plant horizontally round 
its long axis should at the same time obliterate its sensitive- 
ness to contact. The effect of horizontal revolution on these 
plants is like the effect of an anaesthetic on animals. Sensi- 
tiveness is in both cases destroyed temporarily ; in both cases 
growth can take place as usual throughout the period of 
insensibility ; and after the removal of the cause of the insen- 
sibility time must elapse before the organism completely 
regains all its usual powers. 
Though the sensitiveness to contact is destroyed when the 
effect of geotropism is neutralized by revolving parasite and 
host horizontally, yet the sensitiveness to light becomes then 
clearly apparent. Either the heliotropism already existing is 
merely made evident when the effect of geotropism is removed, 
or the removal of geotropism as a factor affecting the behaviour 
of the plant causes it to be more sensitive to light. However 
this may be, by controlling the direction of illumination one 
can cause the tips of the parasite, as it is being revolved 
horizontally with its host on the clinostat, to bend in any 
1 Wortmann, J., Theorie des Windens, Botanische Zeitung, 1886. 
