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 
