110 PLANT LIFE 



on the lines just indicated have other functions 

 besides purely mechanical ones, and these 

 must be adequately discharged if the plant 

 is to be a success. As soon as the foliage 

 is produced, water, is imperatively demanded, 

 and thus there arises, so to speak, a conflict 

 between opposing requirements. The scleren- 

 chymatous tissue is excellent for supplying 

 the needed strength, and its axile position 

 renders it very effective. But it is of little 

 or no use as water-conducting tissue. Now 

 as a matter of fact we find that in the higher 

 types of climbers (e. g. many members of the 

 natural orders Leguminosae, Sapindaceae, 

 Bignoniaceae, etc.), that this strong flexible 

 axile core is succeeded externally, and quite 

 suddenly, by vessels of wide calibre which, 

 though admirable as water conduits, are 

 practically useless regarded from the stand- 

 point of material strength. But the latter 

 defect loses all significance as the plant grows 

 older, for the difficulties that were to the fore 

 in the climber's earlier life become obviated 

 later on in a very simple manner. If one 

 observes an old climber in the jungle, the 

 lower part of the stem is often seen to be 

 lying in snaky coils on the ground, and is 

 evidently not at all exposed to any serious 

 tractive forces. The peculiarity in question 

 is due to the fact that up above, in the roof 

 of the forest, the lower leafy branches of 

 the climber are dying back as they give place 

 to the younger ones springing nearer the 



