CLIMBING AND WATER PLANTS 115 



kind, which indicate that when an organism 

 has once modified its constitution so as to 

 exhibit any special trend, the chances are 

 all in favour of advance along the new lines, 

 and very slightly indeed in favour of a return 

 to the old ones. The history of abortion of 

 parts (e. g. leaves), of concrescence in flowers, 

 and many other morphological series of facts, 

 may be adduced in support of this proposition. 



Thus while stem anomaly is often (but 

 far from invariably) associated with climbing 

 habit, the connection is seen to be, after all, 

 rather obscure. Sometimes perhaps fortui- 

 tous, at others it is to be regarded as the 

 independent, but concomitant, and mutually 

 advantageous result of a modification of 

 the living substance of the plant itself. 

 Finally, it is not unlikely that the abnormali- 

 ties are sometimes elicited as the response, 

 on the part of plants which have the faculty 

 of making them at all, to stimuli given to the 

 living cells by the strains and torsions, as well 

 as by the internal nutritive conditions specially 

 characteristic of the climber, or incident to 

 the climbing habit. 



The same sort of argument may be extended 

 to apply to the well-known fact that in many 

 climbers certain definite organs become modi- 

 fied, and are enabled thereby to attach the 

 plant to a support. The particular organ 

 (Figs. 15 and 16) affected varies widely in 

 different plants, but whether it is a hook, a 

 branch, a leaf, or part of a leaf, it is constant 



