FORMATION OF RUBBER. 35 



believe that latex is an excretory or waste product, even to the proteids, 

 starch, and sugar with which the milky fluid is commonly charged. 

 Protection against insects and snails has also been urged as the function 

 of latex. One of the most recent writers on the subject a reviews and 

 dismisses all the previous suggestions apparently for the reason that 

 none is of general validity and, after detailing numerous observations 

 of his own, comes to the following disappointing conclusion: 



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

 one function common to all laticiferous tubes until microchemical methods are 

 vastly improved or until analyses of latex in its various stages are made. 



Obviously, however, there is no reason why 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-cutting ants, 

 should not be able to attack rubber trees because the gum would dis- 

 able their mouth parts might be an important advantage 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 STRUCTURE 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- 

 amental 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 proto- 

 plasm, with a small nucleus on one side. 6 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 favorable 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 constitu- 

 ents 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 resem- 

 bles that of the cow in being an emulsion. The globules are not, 



a Percy Groom on the Function of Laticiferous Tubes, Annals of Botany, 3: 157, 

 1889. 



b Studien liber den Milchsaft und Schleimsaft der Pflanzen, von Prof. Dr. Hans 

 Molisch. Jena, 1901. 



