ADAPTATION 129 
how the production of the mechanical tissue 
is effected, and how the remarkable and 
evident correspondence between its distribu- 
tion within the plant and the various condi- 
tions imposed by the environment is brought 
about. 
It might seem to be a simple affair to pro- 
duce, or at least to promote, the development 
of mechanical tissue by merely subjecting a 
part of the plant to an artificial stress. But 
even if we could do this, it would still leave 
the kernel of the matter untouched. As a 
matter of fact, however, the attempt has 
often been made, but the results have been 
for the most part entirely negative. Véch- 
ting, for example, endeavoured to induce the 
appropriate formation of strengthening tissue 
by attaching weights to plants in various ways, 
and in a number of different positions. In 
no single instance did he get a clearly positive 
result. But what cannot be done by merely 
applying an external force, can readily be 
accomplished if the requisite nutritive func- 
tions, and perhaps other internal processes 
also, become involved. We know how the 
growth of muscle is stimulated by use, 
consequent, at least in part, on the better 
nutrition which an improved condition of 
circulation ensures. An analogous instance 
is furnished by plants. V6chting, experi- 
menting with certain kinds of cabbages, 
found that after grafting heavy tops on to 
younger and thinner stems the latter forth- 
I 
