220 



the distribution of vegetable forms over the globe, 

 we find that those three families are more nume- 

 rous in species in the low regions of the tropics, 

 we must thence conclude, that a very elevated 

 temperature contributes to the elaboration of 

 the milky juices, to the formation of caoutchouc, 

 albumen, and caseous matter. The sap of the 

 palo de vaca furnishes unquestionably the most 

 striking example of a vegetable milk, in which 

 the acrid and deleterious principle is not united 

 with the albumen, the caseum, and the caout- 

 chouc : the genera euphorbia and asclepias, how- 

 ever, though generally known for their caustic 

 properties, had already presented us with a few 

 species, the juice of which is sweet and harm- 

 less. Such are the tabayba dulce of the Canary 

 islands, which we have already mentioned *, 

 and the asclepias lactifera of Ceylon. Burman 

 relates, that in the latter country, when cow's 

 milk is wanting, the milk of this asclepias is 

 used ; and that the aliments commonly prepared 

 with animal milk are boiled with it's leaves. We 

 may hope that a traveller, deeply versed in che- 

 mical knowledge, Dr. John Davy, will throw 



palms, which yields such sweet and agreeable milky emul- 

 sions, contains no doubt caseum. Of what nature is the milk 

 of mushrooms ? 



* Euphorbia balsamifera. See above, p. 180. The- milky 

 juice of the cactus mamillaris is equally sweet. (De Caridolle, 

 Essai sur lei Propr. mid. des Plantes, p. 156.) 



