336 Evolution and Adaptation 
Land plants have, in addition to the soft parts, the hard 
bast and wood which serves the mechanical purpose of sup- 
porting the soft tissues and protecting them from being 
injured. The arrangement of the hard parts is such as to 
suggest that they are the result of the action of pressures 
and tensions on the plant, for the strongest cells are found 
where there is most need for them. It is easy to imagine, 
Nageli adds, that this important arrangement of the tissues 
is the result of external forces which brought about the result 
in these parts. 
Nageli accounts for the origin of twining plants as follows. 
Being overshadowed by other plants, the stem will grow 
rapidly in the damp air. Coming in contact with the stems 
of other plants, the delicate stem is stimulated on one side, 
and grows around the point of contact. This tendency 
becomes inherited, and the habit to twine is ultimately 
established. 
The difference in the two sides of leaves is explained by 
Nageli as the result of the difference in the illumination of the 
two sides. This influence of light on the leaf has been in- 
herited. The formation of the tubular corolla that is seen in 
many plants visited by insects is explained as the result of the 
stimulus produced by the insects in looking for the pollen. 
The increase in the length of the proboscis of the insect is 
the result of the animal straining to reach the bottom of the 
ever elongating tube of the corolla. ‘The tubular corolla 
and the proboscis of the insect appear as though made for 
each other. Both have slowly developed to their present 
condition, the long tube from a short tube and the long 
proboscis from a short one.” Thus, by purely Lamarckian 
principles, Nageli attempts to account for many of the adap- 
tations between the organism and the outer world. But if 
this takes place, where is there left any room for the action 
for his so-called perfecting principle? Nageli proceeds to 
show how he supposes that the two work together. 
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