172 LECTURE XI. 



(the larger Euphorbiacese) of milk-like fluid. This is usually white, like animal 

 milk, more rarely yellow {C/ieh'donmm) or orange-coloured {Bocconid) ; and the 

 outflow ceases very soon after the injury. This milk-like fluid (the latex), as will 

 be shown more clearly later on, is contained in narrow tubes, generally much- 

 branched or anastomosing. These are the laticiferous vessels, which permeate 

 all the organs of the plants concerned (in some cases perhaps with the exception 

 of the roots) in such a manner that any puncture or cut, however insignificant, 

 opens some of them, and occasions the outflow of the latex. The latex itself 

 consists of two chief constituents ; a watery fluid, and granules or drops, generally 

 exceedingly small, suspended in it, which, as in animal milk, produce the opaque, 

 milky appearance. In the watery fluid are usually dissolved, in addition to the 

 mineral salts which occur in all the fluids of the plant, small quantities of sugar, 

 gum, starch, and proteid-like substances; and, according to circumstances, peculiar 

 alkaloids or vegetable acids and their salts. The substances which cause the 

 latex when drawn off from the plant to form, on mere contact with air, water, 

 alcohol, ether, or acids, flocky coagula which become more or less clumped 

 together and separated from the watery fluid, are still unknown. The small 

 corpuscles suspended in the fluid, which cause the opacity and cloudiness, appear 

 when strongly magnified as round bodies, often almost immeasureably small, 

 in other cases larger. In the latter case, especially in the Ficus-like plants, 

 the corpuscles exhibit a concentric stratification, but are at the same time soft 

 and sticky. These emulsified substances generally show a tendency to cohere 

 among themselves in the latex drawn from the plant ; and so form coherent 

 masses, which after the evaporation of the watery constituent present themselves 

 as dense unctuous mixtures like Opium, or as brittle resins like Euphorbium, or 

 finally as elastic caoutchouc or India-rubber. In dried latex are also found small 

 quantities of wax and fat. The most important product of the laticiferous vessels 

 besides the Opium from Papaver somtii/erimi (which contains Morphia) is perhaps 

 Caoutchouc : this is obtained chiefly from a subdivision of arborescent Brazilian 

 Euphorbiacese {Hevea), Indian species of Fiais, as well as from Apocynaceae and 

 some Asclepiadese. 



The medicinal employment of a variety of kinds of dried latex shows that 

 besides the predominant substances already mentioned, smaller quantities of nar- 

 cotically active alkaloids or other peculiar matters are contained in them. The 

 occurrence of bodies resembling ferments is of especial interest for vegetable 

 physiology. Among these, besides the peptonising ferment in Ficus carica, the 

 Papayotin contained in the latex of Carica papaya is particularly well known ; 

 and, according to the most recent researches, it is not improbable that ferments 

 are distributed in many, or perhaps in most kinds of latex. 



It appears that the laticiferous vessels play a part similar to that of the blood- 

 vessels, and especially the veins of animals. They contain on the one hand matters 

 which find immediate employment in growth; and, on the other hand, secretions 

 and excretions which accumulate in them, and are of no further use. When 

 they contain ferments, their physiological significance is still further enhanced. 

 Of particular interest in this relation also is the existence of starch grains in the 

 latex of many Euphorbiacese ; since, with respect to these, we know that, after being^ 



