192 



detailing numerous observations of his own, comes to the follow- 

 ing disappointing conclusions : 



It seems impossible lo discover what is their futiciioii or to ascertain if there is 

 one functi >n common to all laticiferous tubes until microchemical methods aro 

 vantly improved or until analyses of latex in iis various stages are made. 



Obviously, however, there is no reason wliy it must be believed 

 that all the functions of all milk tubes are the same, or why one 

 function should exclude another. That insects, such as leaf-cut- 

 ting ants, should not be able to attack rubber trees because the 

 gum would disable their mouth parts might be an important ad- 

 vantage in central America, but would not explain rubber in 

 African plants not subject to the depredations of these insects. 

 The most that can be done is to learn the uses of latex in one plant 

 at a time, without anxiety as to whether or not a general function 

 for latex in all plants will be discovered. 



THE STRUC'TURK OF LATEX. 



All the foregoing suggestions and many others seem to have been 

 made before it occurred to anybody to treat the simple but funda- 

 mental question of how the rubber is formed in the milk-bearing 

 tubes. But there is one author at last who has appreciated this 

 point and who has discovered by a close microscopical examination 

 of the rubber globules that each is surrounded by a thin coating of 

 protoplasm, with a small nucleus on one side.* This means that 

 the globules of rubber are produced in the same manner as globules 

 of fat and resin, and like the granules of starch and the crystals of 

 lime, oxalic acid, and other substances which are laid down by the 

 protoplasm of plant cells. If the rubber appeared in the tubes merely 

 by chemical action or because the constituent elements were 

 brought together, this would be an indication favourable to the 

 synthetic production of rubber in the chemical laboratory, and it 

 would mean also that the milk is, if not a solution of rubber, at 

 least a solution of the constituents of rubber. 



There are, however, no observations to indicate that rubber 

 exists in plants except in the form of minute globules, so that the 

 milk resembles that of the cow in being an emulsion. The glo- 

 bules are not, however, naked and free, but each is surrounded by 

 a layer of protoplasm which must contribute a part of the " albu- 

 minous constituents" of the latex if it does not supply all, though 

 this does not make it easier to understand the recent statement of 

 Dr. C. O. Weberf that such materials are not coagulated by boiling. 

 It might be thought that the boiling coagulates the protoplasm of 

 each globule separately and that the rubber is released afterwards 

 and rises to the top, but Dr. Weber's statements would not bear this 

 interpretation, though the absence of an explanation of the sup- 

 posed failure of heat to coagulate any of the albuminous matter 

 leaves the impression that this account of the details is not complete. 



{To be continued.) 



* Studien iiber den Milchsaft und Schleimfaft dd- Pflanzen, von Prof. Dr. Hans 

 Moliech. Jena, 1901. 

 t Tropical Agriculturist, 22:44.^, January, 1903. 



[Issued 16th August, 1904.] 



