CLIMBING AND WATER PLANTS 111 
growing points. Consequently the stem is 
gradually falling downwards as the older 
anchoring branches die and rot away. A 
further cause of the same slackening of the 
stem is to be discovered in some climbers, 
depending on the odd circumstance that the 
growth in length of the stem continues long 
after it would ‘have ceased in ordinary 
plants. 
The general effect of this elongation of the 
stem below the forest roof, in whatever way 
it is produced, is to relieve it entirely of all 
danger from tensile stress. Hence the stem 
can now, to the great advantage of the plant, 
become almost entirely concerned in provid- 
ing the means for the transmission of water 
from the roots to the mass of foliage above. 
A secondary consequence also is to be seen 
in the development of the other tissues by 
which the food material manufactured by 
this foliage is distributed in the plant. If 
much of it is withdrawn to the roots the stem 
is rich in phloém, but it is not especially 
so if, as is generally the case, most of the 
manufactured food is immediately utilised 
in the copious production of flowers and fruit. 
The structure of such specialised climbers 
as these is capable of being interpreted as 
the result of a compromise, so to speak, 
between the opposing functions of nutrition 
and mechanics. The compromise is more 
obvious than in the majority of land plants 
because the issues are more strictly defined. 
