378 



The Supplement to the Tropical Agriculturist 



LATEX AND ITS RELATION TO THE 

 LIFE OF THE PARENT PLANT. 



There are present in many plants chemical 

 substances which, although recognised as pro- 

 ducts of activity of the living cell, neither in 

 their exact mode of formation nor in their full 

 significance are clearly understood. Among such 

 substances are the alkaloids, glucosides, colour- 

 ing matters, ethereal oils, resins and caout- 

 chouc or india rubber. Many of these products 

 are of some considerable economic importance. 

 The alkaloids include strychnine, quinine, mor- 

 phine and other drug ; and violent poisons. Of 

 the glucosides, which are compounds of sugars 

 with various substances, some too are poisonous, 

 yielding on decomposition prnssic acid. The 

 Lima bean or Java bean contains such a 

 glucosido ; and when it is growing wild the per- 

 centage of prussic acid in the stems and leaves 

 maybe sufficiently high to be fatal to animals 

 which feed on it. There is good reason to 

 believe that such a glucoside occurs in the 

 shoots of the Para rubber ; and an example of 

 its poisonous properties occurred several years 

 ago, when some Para rubber trees growing in 

 the garden of the Residency in Taiping were 

 felled because they had proved poisonous to 

 horses. 



Tho presence of such poisonous substances in 

 plants serves no doubt to chock the ravages of 

 animals ; but this cau scarcely be regarded as a 

 primary function. 



The colouring matters in plants serve to 

 attract insects, whose association with plants 

 is frequently beneficial. 



The ethereal oils and resigns are recognised 

 as products of excretion. But the sgnificaro 

 of the relation of these bodies to the economy 

 of tho parent is not cleat. 



The significance of the presence of caout- 

 chouc in plants is, perhaps, still less clearly 

 understood. Caoutchouc occurs in the latex of 

 plants of different natural orders, among which 

 are the Ettpfiorbitcece, including Manihot, 

 Ceara, and Hevea, Para rubber, the Urticacece, 

 containing Ficus, Rambong, and Castitloa, and 

 the Apocynacea: of which Willughbeia and 

 Leuconotis, Borneo rubbers, are members, along 

 with the various natural orders which contain 

 numerous species yielding so-called "gutta- 

 percha." Latex is the name given to a fluid which 

 is either watery or viscous, colourless, white, 

 yellow, orange or red, and is contained in 

 specialised cells, called latex tubes. The cow 

 tree of Venezuela (Galactodendron utile) yields 

 a sweet milk of good flavour; the dried latex 

 of the Poppy (Papaver somniferum) is the opium 

 of commerce; the milky Agarics, fungi of the 

 mushrooms type, yield white, orange or red 

 latex ; and many other species occur which are 

 of interest or of economic importance. 



Latex is an emulsion of various substances in 

 a water-basis; these are resins, caoutchouc of 

 different kinds, oils, tannins, proteids, sugars, 

 starch, alkaloids, ferments and talis. The 

 tube3in which the latex occurs are divided into 



two classes according to their mode of origin, viz. 

 — laticiferous vessels and laticiferous cells ; the 

 former arise by the fusion of independent cells, 

 this class including Manihot and Hevea, while 

 the latter originate by the growth of special 

 cells which are said by some to be differenti- 

 ated in the undeveloped embryo of the seed. 

 These tubes, when fully formed, are living 

 cells connected by branches and frequently for- 

 ming a close network ; they occur in all parts 

 of the plant. 



The tubes, when present, are associated in 

 the stems and leaves of plants with those 

 special tissues to which the function of con- 

 ducting plastic food-ma'erial is ascribed. And 

 this close association, coupled with the rich- 

 ness of the latex in food substances, such as 

 proteid, starch and sugar, suggests at once that 

 the latex tubes function as a conducting system 

 by means of which food material is conveyed 

 from one part of the plant to another. There 

 is other evidence in support of this suggestion. 

 For example, where latex tubes occur, those 

 particular tissues which are normally concerned 

 with the conduction of so-called elaborated food- 

 material are deficient and are frequently badly 

 developed. Again, in Euphorbia, as the young 

 plant commences to develop in the seed the 

 latex becomes poorer; when it has germinated 

 the latex grows richer. And abnormal condi- 

 tions whioh stop certain of the life-processes, 

 notably that of assimilation, make the latex poor. 



Assuming, then, that the tubes serve to 

 conduct food-material in the plant, the ques- 

 tion arises " Is the latex actually in circulation 

 in the plant?" That it is to there is nodoubt, 

 since Schwendener has actually seen it in trans- 

 parent seedlings of Chelidonium. 



From this evidence wo conclude that latex 

 bears some actual 'relation to the economy of the 

 parent, and this relation must be the conduction 

 of plastic food-material. When, by some inter- 

 ference with the normal life-processes of the 

 plant, the latex becomes poor, on the resump- 

 tion of the normal condition it becomes again 

 rich, and the richness in food material has been 

 found to commence in the leave? and to extend 

 to the roots. We can hive no stronger corro- 

 horative evidence than this of the supposition 

 that the latex tubes are a path by which food- 

 material is conveyed in the plant. We, there- 

 fore, concludo in the light of modern concep- 

 tions of the nutrition of plants that the laticife- 

 rous system in plants serves' the purpose of 

 conducting plastic food material. 



In addition, however, to containing food sub- 

 stances the latex contains bodies which are re- 

 garded as " excretory substances." The plant 

 has no means by which it can excrete its useless 

 products outwardly ; and the excretory sub- 

 stances are stored in different parts of the plant 

 body. Such substances are regarded as " end- 

 products '' in the metabolism of the cell and are 

 incapable of being utilised for purposes of 

 nutrition. The resins, gum-resins and gum- 

 mucilages are recognised as excretory products. 

 Such substances are known to occur in latex ; 

 the latex tubes are, therefore, regarded as 

 serving the function of excretion. The oaou- 



