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.
