SELECTED ADAPTATIONS 451 
ing clematises on the other, according as the individuals of 
successive generations were born with the ability to make 
the most of the little light, or the ability to climb into the 
sunshine above. Now, since we are deriving these climbing 
plants from rosette-bearing ancestors it is easy to see how 
rosettes might pass into whorls of a few leaves and the few 
be reduced to two. Weshould then have the opposite leaves, 
characteristic of clematis, arising as an incidental result of 
the development of the climbing habit. So likewise the 
peculiarity of having four sepals, which characterizes the 
genus, may be-an incidental result of the opposite leaf- 
arrangement, for we have only to suppose that such a funda- 
mental change of habit in the growth of the foliage-leaves 
would show also in the arrangement of the floral leaves since 
these would be in a primitive condition readily permitting 
the change. Other changes involved in passing from the 
marsh-marigold-type to the clematis-type of flower and fruit, 
which we have already seen to be advantageous under the 
drier, sunnier, and windier environment, may be easily imag- 
ined to have been effected by the accumulation through 
heredity of innumerable spontaneous variations, each very 
slight but of vital importance to its possessor in the struggle 
for existence. 
According to the view above outlined, more and more 
highly developed groups would be separated from relatively 
primitive ones through the perpetuation of slight yet favor- 
able fluctuating variations, fitting their possessors to occupy 
the more and more trying environment. At the same time 
the more primitive forms would survive under the less exact- 
ing conditions and perfect their simpler structure. Inci- 
dentally there might be preserved through successive genera- 
tions acquired peculiarities of an adaptive sort or even 
nonadaptive ones, provided they were not seriously injurious; 
or, under the same proviso, there might be perpetuated such 
a characteristic feature as the plan of four in the calyx of 
clematis, which had arisen as a merely incidental result of 
some other modification. A peculiarity depending in this 
way upon another peculiarity is called a correlated character. 
Occasionally features of no conceivable use to their possessors, 
