Evidently the several degrees
of deviation, going from three to seven leaflets, may be regarded as
responses to different degrees of variation, and their distribution over
the stems and branches, or over the whole plant, may be considered as
the manifestation of the ever-changing internal tendency to vary.
Considered from this point of view, my plants always showed a definite
periodicity in this distribution, which is the same for the whole plant.
Each of them, and each of the larger branches, begin with atavistic
leaves or with slight deviations. These are succeeded by greater
deviations, but only the strongest axes show as many as seven leaflets
on a stalk. This ordinarily does not occur before the height of
development is reached, and often only towards its close. Then the
deviation diminishes rapidly, returning often to atavistic leaves at the
summit of the stem or branch. I give the numbers of the [363] leaves of
a branch, in their order from the base to the top. They were as follows:
3. 4. 5. 6. 7. 5. 5. 4.
But this is a selected case, and such regular examples of the expected
periodicity are rarely found. Often one or more of the various steps are
lacking, or even leaves with smaller numbers may be interspersed among
those with larger numbers of leaflets.
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