LATEX. 185 



Caoutchouc. There are also found relatively small quantities of fat, and wax-like 

 bodies : of the latter a large quantity is described only in Galactodendron (Solly's Ga- 

 lactin). Resins are abundant, e.g. in the Euphorbias, and in Opium, Caoutchouc, on 

 the other hand, is stated to exist in the latex of very numerous species, belonging to 

 the most various families of Dicotyledons. It forms sometimes the large majority of 

 the constituents which are insoluble in water, as in the Euphorbiacese (species of 

 Hevea), Artocarpeas (species of Ficus, Castillea), Apocynace^ (species of Haucornea, 

 Urceola, Landolphia, Vahea), which yield the Caoutchouc of commerce, to which, 

 according to existing statements, might be added the Asclepiadaceae (Calotropis 

 gigantea) and Lobelia Cautschuk^ In other cases, according to certain unreliable 

 statements, it occurs in small quantities in many sorts of latex, e.g. in that of Lactuca 

 virosa and Papaver somniferum. It is still uncertain whether the constituent described 

 as Caoutchouc or ' india-rubber ' is universally the same chemically distinct body. 

 Further, it is uncertain whether the body or bodies included under this name are the 

 sole constituent of the granules of latex, or whether these each consist of a mixture of 

 different substances. The above-mentioned differentiation of the granules of Ficus, 

 which certainly consist chiefly of Caoutchouc, into layers of different refrangibility, 

 makes the latter view more probable in this case. 



Besides the bodies described, there • are found in the latex of the Euphorbias 

 numerous starch-grains ^. In the herbaceous (Tithymalus) species they are usually 

 of the form of cylindrical or spindle-shaped rods, which in E. Lathyris grow to 55 /ia 

 in length, and lo/x in thickness, in E. Cyparissias to 40 fi in length, and 6/i in 

 thickness ; more rarely they have a roundish form, or (especially in E. Myrsinites) 

 rather swollen ends. In the shrubby and succulent species of hot latitudes they are 

 shaped like a flattened rod, and appear from the narrow side Hnear-spindle-shaped ; 

 seen from the broad side they show a massive broad central part, and much widened, 

 roundish spatula-shaped, often lobed ends ■''. Also in others but by no means all of 

 the Euphorbiacese rod-shaped starch-grains occur in the latex : e. g. spindle-shaped 

 ones in Excsecaria sebifera, Miill., staff-shaped in Hura crepitans ^. How far the blue 

 coloration, which Hartig ^ saw appear with iodine in glycerine in the latex of Cheli- 

 donium, and which Trecul " saw with iodine in that of Nerium, Cerbera Manghas, &c., 

 after boiling with potash, arises from very small starch-granules, remains to be further 

 investigated. 



The above observations, compiled from data at hand, will show sufficiently well how 

 little is known for certain of the anatomy of latex, which has been entirely neglected 

 since MohPs work of the year 1843, and how much may be expected from renewed 

 investigation. The same holds with regard to the chemical conditions. A number of 

 investigations have been made in this direction on sorts of latex, such as Opium, 

 Euphorbium, &c., which are used technically or medicinally, without giving any 



^ Compare on the plants which yield Caoutchouc, Collins, Report on the Caoutchouc of Com- 

 merce, London, 1872 ; Wiesner, Rohstoffe des Pflanzenreichs, p. 153. 



^ Rafn (Pflanzenphysiol. p. 88) first noted them ; they were first recognised as starch by 

 T. Hartig, 1835 ; Erdmann and Schweigger-Seidel, Journ. f. pract. Chemie, Bd. V. p. 4. 



^ Compare Meyen, Physiol. /. c. ; Nageli, Starkekorner, p. 428; Weiss und Wiesner, Botan. 

 Zeitg. 1861, p. 41, 1862, p. 125. 



* Vogl, in Pringsheim's Jahrb. V. ' Botan. Zeitg. 1S62, p. 100. 



* Comptes Rendus, torn. LXI (1865), p. 156. 



