4io SCIENCE PROGRESS 



perhaps not altogether remarkable that the two trees behave 

 differently when tapped. In the former the laticiferous tubes 

 are in mutual connection from the beginning. Special cells 

 are differentiated in the embryo, and these produce by growth 

 in length and ramification the whole laticiferous system of the 

 plant. This is known as the non-articulate system. 



In Hevea, on the other hand, the tubes arise from rows 

 of cells through the breaking down of the intervening walls. 

 The perforations are not always completely formed, so this, 

 the articulate system, is relatively disconnected compared with 

 the other. 



A wound in a tree containing the first arrangement will 

 therefore most likely drain a larger area of laticiferous tissue 

 than one in a tree of the second type. This doubtless accounts 

 for the greater flow of latex from an initial incision in the trunk 

 of Castilloa compared with that from one in Hevea ; but it is 

 difficult to explain the wound-response in the one and not 

 in the other. Perhaps Hevea has a much more extensive, 

 though less communicative, system than Castilloa ; or in other 

 words, a trunk of Hevea has a much larger number of tubes, 

 and so holds a greater quantity of latex, than a corresponding 

 one of Castilloa. At the first tapping the latter gives up 

 practically all its latex, on account of the tubes freely com- 

 municating with one another ; whilst the former only yields up 

 a very small portion of its total quantity of latex, through the 

 comparatively disconnected nature of its system. Thus from 

 a single trial Castilloa appears the better yielder. On re- 

 tapping in a few days' time no more latex exudes. The tubes 

 apparently do not refill with liquid, and so probably collapse. 

 In Hevea, however, a fresh set of tubes will be severed at 

 the second tapping, and if the new incision be made near the 

 old one, the ducts here will probably be surcharged with latex 

 owing to a great infiltration of fluid caused by the previous 

 wounding; thus from such an incision an increased quantity of 

 latex will flow. 



A detailed microscopic study of the laticiferous systems of 

 these two trees might shed some light on the above suppositions. 

 Manihot, however, has a system similar to that of Hevea, and 

 yet, as far as it has been investigated, it shows no wound- 

 response. Johnson, 1 experimenting with this tree in Portuguese 



1 W. H. Johnson, India-Rubber Journal, 1908, vol. xxxv. p. 209. 



