63 
Physiology of the Genus Cu scuta,. 
of but slow growth in length, of considerable increase in thick- 
ness, of active development of haustoria, there follows a period 
of long loose winding, of rapid growth in length, of slight 
increase in thickness, and of no development of haustoria. 
The biological advantage of this alternation in mode of growth 
is great and evident. During the period of rapid growth in 
length the parasite greatly increases the area, often also the 
number of plants, from which it may draw food. During the 
period of slow growth in length it fixes itself at many points 
in this area and develops the haustoria which are to supply it 
with food. The means by which these alternations in mode 
of growth are accomplished must now be considered. 
As stated above, though the seedling will not twine about 
dry and dead organic supports, or rods of glass and metal, 
yet the young plant, feeding itself from the host upon which 
it has fastened, will do so. Hence, in the following experi- 
ments, rods of wood, glass, glass covered with filter-paper, 
wires, strings, and threads, as well as plants, can be used, 
provided none be too large in diameter. It makes also no 
difference, as will be shown presently, whether the rods 
be wetted throughout the course of the experiments or 
remain dry. 
If now one of the objects named be brought into contact 
with one of the young and rapidly developing lateral branches, 
or with the main stem when it begins rapidly to grow after 
forming haustoria, though the contact be carefully maintained, 
either by frequently moving the rod in correspondence with 
the change in direction or the increase in length of branch or 
stem, or by fastening the branch or stem to the rod in any 
way (best by a narrow ribbon of gummed paper), the Cuscuta 
will make no close turns about the support. If it follows the 
support, as the more or less erect main stem is likely to do, 
and as the more nearly horizontal branches are not likely to 
do, only a long, steep, loose spiral will be formed. After 
a time, however, the growth decreases in rapidity. If now 
a contact be made about three centimetres from the tip, the 
stem or branch will bend sharply and, in the course of fifteen 
