65 
Physiology of the Genus Cuscuta. 
at once induced the usual turning of the tendrils. At 
Professor Pfeffer’s suggestion I undertook to test the irrita- 
bility of Cuscuta by means of gelatine. If the Cuscuta wound 
about a rod coated with wet gelatine, forming short close 
turns, there must be some reason other than contact-irritation 
(perhaps a chemical one) for their formation, for Cuscuta does 
not of itself and unstimulated make such close spirals ; though 
old tendrils which have not succeeded in finding a support 
normally do. If, on the other hand, the Cuscuta made only 
long, steep turns, if any, we should have positive evidence in 
support of the idea of contact-irritation. 
According to the paper just cited, it makes no difference in 
its effect on tendrils whether the gelatine be simply soaked 
in water till it will absorb no more, or whether it be dissolved 
in proportions of eight per cent, or less in water. For reasons 
of mechanical convenience I preferred to use concentrated 
gelatine. I coated, as smoothly as possible, a glass rod of two 
or three millimetres diameter and twenty centimetres length, 
for a distance of fifteen centimetres, with gelatine to which 
only enough water had been added to make it rather soft 
when heated over a water-bath. In order to allow for its 
absorbing more water and swelling later, the coat of gelatine 
was made not more than two millimetres thick at this stage. 
Around one end, the end of the rod not coated, I wound 
several layers of filter-paper, enclosed this in stififer paper, 
and tied it fast together, thus making a cup, out of the bottom 
of which, when the rod was held vertical, water could flow in 
a thin sheet over the whole rod of gelatine. Into a chamber 
made of a bell-jar held mouth upwards on a retort-stand (as 
shown in the annexed woodcut), covered by a glass plate 
pierced in the centre by a hole one and a half centimetre in 
diameter, and kept moist by a thick band of wet filter-paper 
(a) laid inside, I introduced a branch of Cuscuta Epilinum (c). 
Through the hole in the glass plate above I passed the 
gelatine-coated glass rod (g\ fastening it at the top and 
resting its lower end in the mouth of a tube (d) which ran 
to a catch-bottle (b) below. From a reservoir (tv) above 
