And this is confirmed by the almost universal absence of
two-bladed clover-leaves.
Considering the deviation as an anomaly, we may look into its nature.
Such an inquiry shows that the supernumerary leaflets owe their origin
to a splitting of one or more of the normal ones. This splitting is not
terminal, as is often the case with other species, and as it may be seen
sometimes in the clover. It is for the most part lateral. One of the
lateral nerves grows out becoming a median nerve of the new leaflet.
Intermediate steps are not wanting, though rare, and they show a gradual
separation of some lateral part of a leaflet, until this division
reaches the base and divides the leaflet into two almost equal parts. If
this splitting occurs in one leaflet we get the "four-leaved" Clover, if
it occurs in two there will be five leaflets. And if, besides this, the
terminal leaflet produces a derivative on one or both of its sides,
[343] we obtain a crown of six or seven leaflets on one stalk. Such were
often met with in the race I had under cultivation, but as a rule it did
not exceed this limit.
The same phenomenon of a lateral doubling of leaflets may of course be
met with in other instances. The common laburnum has a variety which
often produces quaternate and quinate leaves, and in strawberries I have
also seen instances of this abnormality.
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