378 



A most interesting and obscure point was raised by him re the 

 connection of the laticiferous system to the vital processes of the 

 plant ; as this is a subject of profound practical interest it will not 

 be out of place to inquire into that connection. 



Mr. Wright, in alluding to the feeding of the laticiferous system , 

 referred to a section of interest in that apposition was seen on the 

 part of a milk tube with a vessel in the young wood. The question 

 to begin with is, what is latex ? It is generally thought to be a 

 waste product, but an analysis of latex (in F. elastica) shows that it 

 contains proteids, carbohydrates, the emulsion being due to the 

 suspension of the " rubber element" in the mother fluid. 



It is interesting to know why a single species plant requires such 

 a large system for the storage of its products, while the general 

 tendency of plants do not point in the same direction. 



As pointed out the latex tubes occur in the " bark " in the rubber 

 tree and do not encroach upon the xylem. If we turn to other trees 

 we see that the tree as a whole takes part in the deposition of its 

 waste products. Thus in Pin us the resin passages occur in second- 

 ary xylem, while in other plants raphides are seen deposited in the 

 vessels of the plant. Besides it is interesting from this point of 

 view to recall that distinct milk passages can be observed in the 

 stipules of the F. elastica, and we know that of all forms of modified 

 leaf the stipules come nearest the original. 



Let us inquire whether there are any data for suggesting that 

 latex may be in its earlier stages a food for the plant. We know 

 that in all green-leafed plants starch granules can be seen in the 

 guard-cells round each stomata. There is reason to believe that the 

 change of carbon dioxide to starch takes place through the interme- 

 diation of the formation of prenic aldehyde, the later stages being 

 only concerned with hydrolyses and polymerisations, two processes 

 easily attained in the plant owing to the large cell surfaces in- 

 volved. 



Pushing this physiological fact further we know that the starch 

 can be used by the organism only as sugar, and the excess of starch 

 is deposited in various parts of the tree. 



Keeping in mind the properties of living protoplasm in the direc- 

 tion of selection and polymerisation it is not difficult to imagine that 

 the carbon dioxide may be changed to a member of the acetylene 

 series, Isoprene either directly by the phenomena of hydrolysis 

 and polymerisation or by more complex changes. 



We know as a matter of fact that the decomposition products of 

 rubber give isoprene and levulinic acid, of which more anon. Iso- 

 prene, though of the open series of carbon compounds, like the 

 other members of its series, readily polymerises to dipentene of the 

 terpenes and of the closed or ring carbon compounds ; the formula 

 for dipentene is (C 10 H I6 ; now on the distillation of the "rubber 

 element " Caoutchouc we get the identical isoprene and dipentene 

 and the formula (empiric) of Caoutchouc is (C 10 H 16 )n: This is of 

 importance as showing that Caoutchouc is a polymer of dipentene. 



