240 BOTANY part i 



verted by oxidation into indigo. Woad (Isatis tindoria) contains, on the other 

 hand, the related glucoside isatin. Coniferin, which is present in the cambial 

 sap of the Conifers, has recently acquired an economic value, as from it vanillin, 

 the aromatic principle of vanilla, maj' be artificially produced. In this process the 

 coniferin is decomposed, by the action of a ferment or acid, into glucose and 

 coniferyl-alcohol, by the oxidation of which its aldehyde, vanillin, is formed. 



It is as yet unknown what part in the metabolic processes of plants is performed 

 by the bitter principles, suchas theLUPULiN of Hops, ALOiNof Aloes, absynthin 

 of Wormwood. There is the same uncertainty with regard to the functions of the 

 alkaloids. Since most alkaloids, strychnine, brucine, veratrine, coniine, 

 muscarine, atropine, quinine, morphine, codeine, aconitine, colchicine, 

 nicotine, pilocarpine, cocaine, together with caffeine (theine) and theobro- 

 mine, Avhicli are closely related to nric acid, and many others are violent poisons, 

 they furnish a certain protection to plants against destructive animals. This, 

 however, does not preclude the possibility that they may at the same time have 

 an important physiological significance. Thus, according to Treub, hydrocyanic 

 acid plays the same part in the formation and transport of proteids in Pangium 

 edule and Phaseolus lunatus as the amides do in other plants. It must, however, 

 be noted that alkaloids are also jioisonous to the protoplasm of the plant. 



The COLOURING matters and ethereal oils, although present only in 

 small quantities, make themselves particularly noticeable to the senses of 

 sight and smell. They probably represent only by- and end-products of meta- 

 bolism and, with the exception of chlorophyll, take no further part in the vital 

 processes of plants, except in so far as they are beneficial to the general well-being 

 by enticing {e.g. flowers, fruits) or repelling {e.g. by warning colours) animals. 

 Their oecological significance is accordingly much better known than their iihysio- 

 logical functions. Just as the ethereal oils are frequently found in special excretory 

 receptacles, the resins, gum-resins, and gum-mucilages, which are also excretion 

 products, are usually deposited in canals or glandular cavities, and are often mixed 

 with ethereal oils. Whether their formation in tlie particular instances is necessary 

 for the carrying out of the normal processes of metabolism is altogether uncertain. 

 They are, at any rate, useful to j^lants when wounded, serving as a protection 

 against evaporation and the attacks of parasites. On a square centimetre of the 

 surface of the splint- wood of the Pine, sixty to seventy resin canals open, and the 

 wood contains, according to Mayk, 22 kilos of resin in every cubic metre. 



The significance in the economy of the plant of the so-called india-rubber 

 (caoutchouc) and gutta-percha in the latex is still less known. In addition to 

 these substances, there also occur in latex, resins, ethereal oils, alkaloids (in 

 opium), leptomin, starch grains, and other carbohydrates, oil-drops, and albuminous 

 substances. The presence of these substances, valuable as constructive material, and 

 occasionally also of active enzymes (peptonising ferments are found in the milky 

 juice of Ficus Carica and Carica Ta/paya), in the latex, gave rise to the suggestion 

 tliat the latex cells and tubes function in the transport of the nutrient matter. 

 Our present knowledge of these often caustic and poisonous saps is limited to their 

 external utility in the economy of plant life. By their obnoxious properties they 

 defend plants from the attacks of enemies. Also, in the event of plants being 

 wounded, the latex is pressed out either by the surrounding turgescent tissue or by 

 the tension of the elastic walls of its own cells, and forms, as it quicky coagulates 

 in the air, an etiicient covering for tlie wound. In other jjlants, especially in trees, 

 wound-gum serves the same purpose. (Pp. 1-13, 162.) 



