226 BOTANY PART i 



dilute acids are broken up into glucose and other derivative products. It is con- 

 ceivable that the formation of glucosides (and tannins) serves to locally fix 

 substances which otherwise would readily diosmose. It might even be suggested 

 that the jtolysaccharides, starch and cellulose, might be regarded as glucosides of 

 the sugars themselves. In the Amygdalaceae (Bitter Almonds, Plum seeds) 

 AMYGDALIN is found which on fermentation yields hydrocyanic acid in addition to 

 benzaldehyde. The Lima or Java beans (P/iaseolus lunatus), which of late years 

 have been used for feeding cattle, also liberate from a glucoside hydrocyanic acid. 

 In the wild form this may be in such quantity (0'16 per cent) that fatal poisoning 

 has resulted. From a similar cause Sorghum, Glyceria, and Lotus may be more or less 

 poisonous. Glucosides appear in the Solanaceae as the poisonous SOLANIN, in the 

 Cruciferae (mustard seeds) as MYKONIC ACID, in the bark of the Horse-chestnut as 

 extremely fluorescent .&SCULIN, in species of Digitalis as the poisonous DIGITALIS', 

 and in the cortex of Willows as SALICIN. Certain plants (Indigofera, Polygonum 

 tinctorium) contain INDICAN, the glucoside of indoxyl ; the latter substance is con- 

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

 hand, the related glucoside ISATIN ( 46 ). 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, may be artificially produced. In this process the 

 coniferin is decomposed, through 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, such as the LUPULIN of Hops, ALOIN of Aloes, ABSYNTHIX 

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

 ALKALOIDS. Since most alkaloids, STRYCHNINE, BRUCINE, VERATRINE, CONIINE, 



MUSCARINE, ATROPINE, QUININK, MORPHINE, CODEINE, ACONITINE, COLCHICINE, 



NICOTINE, PILOCARPINE, COCAINE, together with CAFFEINE (theiue) and THEOBRO- 

 MINE which are closely related to uric acid, and many others are violent poisons, 

 their vegetable bases and repugnant bitter principles 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 as the amides do in 

 other plants. It must, however, be noted that alkaloids are also poisonous to 

 the protoplasm of the plant ( 4? ). 



The COLOURING MATTERS AND ETHEREAL OILS, although in actual weight present 

 only in small quantities, make themselves particularly noticeable to the senses of 

 sight and smell. They probably represent only bye- 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.y. by warning colours) animals. 

 Their cecological significance is accordingly much better known than their physio- 

 logical function. 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 the particular instances is necessary 

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

 They are, at any rate, useful to plants 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 MAYR, 22 kilos, of resin in every cubic metre. 



