103 
Physiology of the Genus Cu scuta. 
a close, nearly horizontal turn about the host, the curved part 
still continues .for >a time to grow in length. It is true that 
this growth is neither rapid nor of long duration, yet it is 
sufficient to loosen the spiral somewhat, to weaken the con- 
tact, to reduce the stimulus for haustorial formation, to lessen 
the force which the growing haustoria can bring to bear on 
the host, by increasing the distance through which they must 
grow. However, accompanying and following this compara- 
tively slight growth in length is a very considerable and long- 
continued growth in thickness. The result of this latter is 
more than to counterbalance the growth in length. It main- 
tains the closeness of the spiral, it constantly increases the 
intimacy of the contact, it strengthens thereby the stimulus 
for haustorial formation, and supplements the force which the 
growing haustoria can bring to bear on the host, by reducing 
the distance through which they must grow. This growth in 
thickness further supplements the force by (first) causing the 
stem of the parasite to press against and thus to compress 
the host by its whole concave side, and not merely by the 
swellings over the young haustoria ; and (second) by increas- 
ing the rigidity of the coils so that, firmly braced by the 
coiled stem in which their strong bases are embedded, the 
haustoria can apply all their force forwards and against the 
host. Besides, the parasite is not merely closely pressed 
and firmly held against the host, but, as I shall demonstrate, 
is actually attached to it by many of the epidermal cells 
covering the swellings over the haustoria. 
That the stem of the parasite, whether it bear haustoria or 
not, and whether it be coiled closely or only steeply and 
loosely around the host, exercises a very considerable pressure, 
might be suspected from its resemblance to tendrils and 
twining stems, but it may be made quite evident by the 
simple method used in demonstrating, though not thereby 
measuring, the pressure of tendrils, and the relative pressures 
developed by the two sorts of coils will at the same time be 
indicated. Let a branch of Cuscuta which is irritable, and 
therefore in condition to make close turns, be brought into 
