184 LATICIFEROUS TUBES. 



bodies (said to occur, e.g. in species of Lactuca), further tannin in many plants, espe- 

 cially the Aroidece, INIusa, also in the Cichoraceoe, and Euphorbia Lathyris : peculiar 

 constituents soluble in water are found in many sorts of latex used officinally in the 

 dry state, as e. g. morphin combined with meconic acid in opium ; and lastly, the 

 greater part of the ash which appears in analyses. As regards the form in which 

 the latter occur in the living plant it should be mentioned that salts of malic acid, 

 especially malate of lime, occur in very large quantity in the latex, at least of many 

 Euphorbias. In the officinal Euphorbia (E. resinifera, Berg) the latter salt is found 

 in large quantity : in the latex of one-year-old plants of E. Lathyris it occurs in 

 autumn in so large quantity that when a drop of latex escapes into the air it imme- 

 diately precipitates innumerable crystals '. 



As soon as latex comes in contact with the air, and still more quickly on treat- 

 ment with water, alcohol, ether, or acids, coagula appear in the hitherto apparently 

 homogeneous, clear fluid itself, and independently of the aggregation of the insoluble 

 bodies, described by Mohl (Bot. Ztg. 1843, No. 33). The coagula collect together, 

 and separate with the insoluble bodies from the clear fluid. These phenomena of 

 coagulation, which appear under the action of so various agencies, point especially to 

 a complicated composition of the fluid, and deserve further investigation. 



The suspended bodies are present in the fluid in varying quantity, and the 

 cloudiness of it is also variable, according to the age of the part, and according to 

 the species : e. g. Morus, Nerium, and Stapelia show slight cloudiness ; most species 

 of Ficus and Asclepias have dense white milk. Excepting the starch-grains of the 

 Euphorbias, which will be described below, the bodies have the form of round 

 granules. They are in most cases — e. g. Euphorbia, and all plants with reticulate 

 tubes — immeasurably small, and, when in free drops, they show active Brownian 

 movement. The latex of the Artocarpeas and Moreae shows larger granules. They 

 have in Ficus Carica an average diameter of 3/x(i.4/x to 5.6^), and show 

 concentric stratification, as found by Caruel ^ the larger having three layers of 

 almost equal thickness surrounding a small nucleus, the smaller only two layers. 

 The outermost layer is sharply distinguished by different refrangibility from the inner 

 ones. The granules of the latex of Ficus elastica, Broussonetia papyrifera, Madura 

 aurantiaca, have in the main the same structure ; also, though less distinctly, the very 

 variously sized ones of Morus nigra : all these granules are soft and sticky, and readily 

 adhere and collect together after leaving the plant. 



The slightly milky latex, which escapes from young petioles of Nerium Oleander, 

 contains pale, apparently homogeneous, spherical bodies of unequal size, two or more 

 of which are often adherent to one another : the larger of these exceed those of the 

 Fig. in size. IVIuch larger spheres are described in the case of Musa. 



On the chemical nature of the granules the existing chemical analyses tell us that 

 — leaving out of account relatively very small quantities of substances characteristic of 

 special cases, such as the alkaloids of Opium, which are insoluble in water — they may 

 be generally designated on the one hand as resins, on the other as consisting of 



* The chemical definition of the crystals I owe to the kindness of Professor Fliickiger. 

 ^ Sur les granules particuliers du sue laiteu.x du figuier, Bull, de la Soc. Bot. de France, XII 

 (1865), p. 273. 



