18 



THE AGRICULTURAL NEWS 



January 20, 1912. 



probably known of the significance of the presence of 

 this, or of the substances that produce it, than has been 

 ascertained regarding the manner of formation and func- 

 tion of other bodies, such as ethereal oils, resins, colour- 

 ing matter, alkaloids and glucosides. Latex itself con- 

 tains, in a watery medium, resins, rubber, oils, tannins, 

 proteids, sugars, starch, alkaloids, ferments and salts. 

 It occurs, in plants, in tubes of two kinds, called 

 laticiferous vessels and laticiferous cells, the former 

 originating by the joining together of independent 

 cells and the latter by the special growth cf cells whose 

 origin is said to be traceable even when the plant is an 

 embryo contained in the seed. In either case, the 

 tubes are living cells connected by branches to form 

 a close network extending throughout the plant. 



The interest of these late.K tubes is increased fur- 

 ther whea regard is paid to the circumstance that, when 

 they are present, they are associated in the stems and 

 leaves with the system of vessels which carries to all its 

 parts the food that has been manufactured by the 

 plant. The circutnstance of this association, combined 

 with the fact that, as has been indicated, latex is rich 

 in substances that are of nutritive value to the plant, 

 leads to the suggestion that the tubes in which the 

 latex is carried have their use as a means of conveying 

 food material from one \nxrt of the plant to another. 

 This suggestion receives support from the fact that, 

 where latex tubes are well developed, the plant food 

 carrying tissues that are normally present in ordinary 

 plants are often much less strongly developed, and 

 there is the additional circumstance that latex in the 

 seeds of Euphorbia becomes poorer in food bodies dur- 

 ing germination, only to gain an increase in these use- 

 ful substances when the young plant becomes self- 

 supporting. The argument for the validity of the sug- 

 gestion only reipiires completion by the experimental 

 assumnce that the latex actually travels through the 

 tissues of the plant; this has been obtained by Schwen- 

 dener, who has observed the circulation of latex in trans- 

 parent seedlings of Chelidonium, It is therefore con- 

 cluded that the ti.s.sues carrying latex in plants are 

 concerned in the conduction of food materials that are 

 of use in their nutrition. 



The latex tubes possess, however, another use. 

 As has been stated, the milky juice in them also con- 

 tains substances that cannot be made use of by the 

 plant, as food. These are called excretory substances, 

 or end products, the latter designation being applied 

 because, as far as is known, they cannot be converted 

 by the plant into any kind of bodies that may be use- 

 ful in feeding the organism. Among end products are 



included the resins, gum-resins and gum-mucilages, 

 and their presence in the latex tubes points to the use of 

 these in serving the function of excretion. It is probable 

 that, as far as rubber is concerned, this does not 

 actually exist as such, in the latex; but that it is 

 formed, during coagulation, from simpler, similar bodies. 

 Caoutchouc is therefore regarded as an end product; 

 though the real significance of the fact that it can be 

 formed in latex is not yet understood. It can only be 

 stated that the presence of enzymes in the latex, 

 together with the other substances, is suggestive of the 

 usefulness to the .j)!ant of the possibility that quick 

 changes may take place in its composition. 



Huch considerations have reference to the essential 

 part that latex may play in regard to the jihysiological 

 processes that are necessary to the life of tlie plant. In 

 dealing with them, it must not be forgotten that the 

 property of the juice of a plant to coagulate, when it 

 has been damaged, is of much assistance toward the 

 healing of wounds; that the presence of hairs contain- 

 ing latex, on the leaves nearest to the flowers, serves 

 sometimes to protect these from hui't by animals; and 

 that certain of the last are prevented from attacking 

 many plants, through their possession of a latex con- 

 taining poisonous substances. It is considered, however, 

 that these functions are incidental. The real i\inctions 

 of latex, as has been explained, are regarded as being 

 nutritive and excretor}'. 



The present position of the subject is summarized, 

 at the end of the article, as follows. 'The relation of 

 the latex to the life of the parent possesses far more 

 than a scientific interest. The recognition of the lati- 

 ciferous tubes as a means of conducting plastic food 

 material is of itself of i)rimaiy importance inasmuch 

 as such problems of practical importance as tapping, as 

 systems of tapping, bark renewal, etc., are closely con- 

 nected with it, while an accurate knowledge of the sig- 

 nificance and mode of formation of caoutchouc must be 

 of considerable value to the practical cultivator.' 



luformatioff' received from Dominica shows that the 

 plant distribution by the Agricultural Department in that 

 island, during ] )ecember 1911, comprised .5,807 plants, 

 including limes 3,82.5, spineless limes 200, cacao 275, Para 

 rubber 1,300, sour orange 100, grafted mangoes 13, budded 

 citrus 12, miscellaneous 12. In Antigua, the following 

 distribution was made, in the same month: limes 3,35.3, 

 miscellaneous 181, cacao 56, cocoa-nuts 50, cane plants 6,600. 



