MOVEMENTS OF LATEX 343 



Even in the present imperfect state of our knowledge, however, we may 

 confidently assert that the latex of a great many plants contains a 

 large proportion of plastic material, which is subsequently utilised for 

 purposes of nutrition. The far-famed Cow Tree {Brosimum Galacto- 

 dcndron), for example, produces large quantities of a sweet and palatable 

 latex, which is used in its native country in place of cow's milk ; in 

 this case no one would be disposed to regard the latex as a means of 

 protection against animal foes, or to suppose that the laticiferous system 

 is merely a repository for useless excretory products. 



Various circumstances indicate that actual streaming of the latex 

 takes place within the intact laticiferous system. The dilution of the 

 latex which occurs in starved plants presupposes a dispersal of the 

 solid particles in the liquid matrix, quite apart from the question 

 whether some of the particles of oil, resin, etc., are absorbed or not ; 

 but, as Schwendener has pointed out, this dispersal cannot be effected 

 on any considerable scale without displacement of the latex en masse. 

 In Euphorbia the behaviour of the suspended starch grains also throws 

 some light on this question. Schwendener states that, in the foliar 

 latex-tubes of Euphorbia splendens, the starch-grains are all minute and 

 rod-shaped, without expanded ends. In the stem, a few centimetres 

 below the insertion of a leaf, every intermediate stage may be found 

 between larger simple rods and the peculiar dumb-bell-shaped grains 

 which never occur in the foliar tubes. The obvious inference is, that 

 the rod-shaped grains migrate from the leaf to the stem, and there 

 gradually assume the dumb-bell shape ; such a migration, however, 

 necessarily implies a bodily displacement of the latex. The latex-tubes 

 of Euphorbia sometimes become obstructed at certain points ; where 

 this has happened, microscopic examination reveals a dense mass of 

 starch-grains adhering to one side of the obstruction. Evidently the 

 obstructing body acts as a filter, which holds back the starch-grains but 

 allows the liquid portion of the latex to pass. Schwendener, finally, 

 actually observed a jerky movement of the latex in transparent seedlings 

 of Chelidonium majios, which were transpiring actively through their 

 leaves or roots. 



We are thus led to consider the sources of the energy that is 

 employed in transporting latex. The liquid contained in the intact 

 laticiferous system is exposed to very considerable pressure, as is shown 

 by the fact that it often exudes in large quantities if the tubes are cut 

 open. Where the latex-tubes are thin-walled, the pressure is most 

 probably due to the turgor of the surrounding parenchymatous tissues. 

 In various species of Euphorbia, Schwendener was able to prove the 

 existence of an independent turgor-pressure within the latex-tubes 

 themselves, which produces an elastic extension of their walls. When 



