10 
that many of the plants of these families are remarkable 
for the strength and tenacity of the fibre they yield for 
rope-making: secondly, that bird-lime is prepared from 
plants belonging to families which yield caoutchouc, as 
from the apocyneous Voacanga in Madagascar ; and in 
India, from different species of Ficus and Jrtocarptis. 
But the most interesting fact which I obtained from the 
investigation, was one most unexpected, and the least 
connected with the subject. Having been previously 
employed in considering the proper means for extending 
the cultivation of silk in India ; it struck me as singular, 
that so many of the plants which silk-worms prefer next to 
the mulberry leaf, should be found in those families which 
yield caoutchouc. Thus, in England, the lettuce and 
dandelion leaves, belonging to Cichoracece, and in India 
Ficus religiosa, belonging to the Artocarpece, have been 
ascertained to be the best substitutes for the leaves of 
the mulberry; while the Arindy silk-worm of India, 
Phalcena Cynthia, feeds upon those of the castor oil 
plant, Ricinus communis, belonging to Euphorbiaceoe.*. 
Considering that a circumstance of this nature was not 
likely to be accidental, I was induced to think that it 
depended upon the presence of some principle common to 
all these vegetables, and therefore that caoutchouc (perhaps 
in a modified state) might really be contained in the juice 
of the mulberry, though this is described as not being 
milky. I therefore requested Mr. Sievier, who has made 
so many discoveries in the properties of caoutchouc, to 
ascertain whether my conjecture was well founded. In a 
* Since this lecture was delivered, I have seen in the newspapers, that 
a species of Scorzonera, which belongs to the natural family of Cichoracece, 
has been found to be a good substitute for the mulberry-leaf in France. I 
have also been informed by Mr. Morley, that a caterpillar which forms a 
very large caooon, and spins a tough but coarse kind of silk, feeds on the 
leaves of the South American caoutchouc-tree, Siphonia elaslica. 
