Physiology of the Genus Cuscuta. 1 1 5 
the host The starch-grains in the cells thus attacked and 
penetrated disappear, being dissolved and consumed by the 
protoplasm of the cells which contain them, or by the intruders ; 
by which, it is of course impossible to tell. 
We have seen that the penetration of the host by the parasite 
is begun by the pre-haustorium overlying the young hausto- 
rium proper, and that this is accomplished by the combined 
action of pressure and solution. The time and the field of 
action of the pre-haustorium are manifestly limited owing to 
its position, for the growing haustorium must finally crush 
and push through it. Some arrangement must be made to 
continue the work of the pre-haustorium, and this is effected by 
the cells at the tip of the haustorium, cells corresponding in 
position to those of the cap of a typical root. They become 
in appearance as in function like those composing the pre- 
haustorium, long, slender, thin-walled, with abundant proto- 
plasmic contents and large nuclei, and great capacity for 
growth. 
Summary. 
The results of the experiments described in the preceding 
pages may be briefly summarized as follows. The genus 
Cuscuta comprises parasitic climbing plants with two distinct 
modes of twining. At certain stages they resemble the 
majority of twining climbers in that they twine steeply, and 
only tightly enough to secure necessary mechanical support. 
They do not twine about horizontal rods whether they them- 
selves be erect or horizontal. They twine in the direction in 
which they nutate ; so far as I have been able to see, always 
in the reverse direction of the hands of a watch. At other 
stages, which regularly alternate with the foregoing, they 
make short, close, much more nearly horizontal turns about 
a vertical support, thereby embracing it closely and bringing 
their concave surfaces into intimate contact therewith. The 
former turns are made solely in consequence of the climbing 
habits of the plant, by the combined effects of circumnutation 
