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in the plant?" That it is so there is no doubt, since Schwendener has 

 actually seen it in transparent seedlings of Chelidonium. 



From this evidence we 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 interference with 

 the normal life-processes of the plant, the latex becomes poor, on the 

 resumption of the normal condition it becomes again rich, and the 

 richness in food material has been found to commence in the leaves 

 and to extend to the roots. We can have no stronger corroborative 

 evidence tlian this of the supposition that the latex tubes are a path 

 by which food-material is conveyed in the plant. We, therefore, 

 conclude in the light of modern conceptions of the nutrition of plants 

 that the laticiferous system in plants serves the purpose of conducting 

 plastic food material. 



In addition, however, to containing food substances the latex 

 contains bodies which are regarded as "excretory substances." The 

 plant has no means by which it can excrete its useless products 

 outwardly; and the excretory substances 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 caoutchouc in all probability does 

 not exist as such in the latex, but is produced .during coagulation 

 from simpler bodies similarly constituted chemically. It is itself a 

 compound of carbon and hydrogen and is chemically comparatively 

 inactive. There is, therefore, some probability that it is an end-pro- 

 duct and incapable of being further utilised by the parent. Much 

 more requires to be learnt, however, concerning the changes which 

 occur in latex in different parts of the plant and under different 

 conditions, before any accurate conclusions can be arrived at as to the 

 significance of the presence of caoutchouc. 



Enzymes have been demonstrated in the latex of some plants, 

 Ficus Carica and Carica papaya (papaw) contain peptonising enzy- 

 mes. The presence of an oxidase has been demonstrated in the latex 

 of Hevea ; the occurrence of black latex is ascribed this enzyme. The 

 presence of enzymes is significant of the occurrence of active 

 changes in the latex. 



In addition to the above mentioned functions of latex two others 

 occur, viz. — the sealing of wounds and the protection of the plants 

 from animals. Latex containing caoutchouc coagulates quickly, and 

 the coagulated mass serves to seal wounds more or less effectively. 

 In some plants the latex tubes branch close to the surface and thus 

 facilitate the sealing of wounds by the juice. In other plants hairs con- 

 taining latex are present on the floral bracts and are thus regarded as 



