456 Proceedings of Philosophical Societies. [June, 



upon his authority, have given the name of persea to a species of 

 laurel, an opinion which is the less admissible as this lauret 

 comes ft'om America. Others, as Schreber, have fancied they 

 found it in the sebestier (cordia mixa) whose viscous fruit is, 

 however, quite different. M. Delisle was more fortunate, having 

 observed in a garden in Cairo a specimen of the tree called by 

 Linnaeus ximenia (Egyptiaca, he perceived it possessed most of 

 the characters of the persea, the height was from 18 to 20 feet, 

 the branches thorny, and the oval perennial leaves more from one 

 inch to an inch and a half in length, which traits may have 

 occasioned its com))arison with the pear tree ; its fruit is in the 

 form of the date ; is sweet when, ripe, and contains a kernel 

 which is rather ligneous. When M. Delisle arrived in Upper 

 Egypt, he met with two others, and he, learned from the inhabi- 

 tants of the higher country, that it is common in Nubia and in 

 Abyssinia, and much esteemed in Dafour. Nevertheless he 

 could not learn whether the inner part of the wood is black, as 

 the ancients say is the case with respect to their persea. 



The tree is now called in Nubia es.Ui'. M. Delisle remarked 

 in it peculiarities sufficiently marked to separate it from the 

 other ximenia, and he made it a genus, to which he gave thq 

 name of balanites. 



Among the vegetables, which furnish a juice of a milky appear- 

 ance, one of the most remarkable is that which the Spanish 

 colonists have called the cow tree, because its milk, far from 

 having, like that of the spurges and most other lactescent plants, 

 acrid and pernicious qualities, yields, on the contrary, a whole- 

 some and agreeable beverage. M. de Humboldt read to the 

 Academy a description of this tree, and of the experiments made 

 upon the juice which it supplies. This celebrated traveller, not 

 having been able to see it in flower, has not settled its genus ; 

 but to judge from its fruit, it seems to belong to the family of the 

 sapotillse ; it is tall ; its leaves are eight or ten inches long, alter- 

 nate, coriaceous, oblong, pointed, and marked with lateral and 

 parallel ribs. 



■ When incisions are made in it, a glutinous milk runs out, with 

 a very pleasant balsamic smell, of which the negroes drink large 

 quantities, dipping into it maize bread, or tapioca, and this food 

 sensibly fattens them. When exposed to the air, some pelli- 

 cles are formed on the surface which acquire as they dry some- 

 what of the elasticity of the caoutchouc, and a curd is separated, 

 Avhich becomes sour in time, and to which the common people 

 give the name of cheese. 



M. de Humboldt takes this opportunity of making some gene- 

 ral reflexions on the different vegetable milks, whose injurious 

 quahties depend on certain poisonous principles, which exist in 

 a sufficiently large quantity to produce sensible effects, such as 

 the morphiuui in opium, but in the most poisonous faiiulies., 



