in itself, and thereafter it can
be associated by crossing with other existing characters to produce a gamut
of new varieties. If, for example, the character of hooding in the standard
(cf. Pl. II., 7) suddenly turned up in such a family as that shown on Plate
IV. we should be able to get a hooded form corresponding to each of the
forms with the erect {84} standard; in other words, the arrival of the new
form would give us the possibility of fourteen varieties instead of seven.
As we know, the hooded character already exists. It is recessive to the
erect standard, and we have reason to suppose that it arose as a sudden
sport by the omission of the factor in whose presence the standard assumes
the erect shape characteristic of the wild flower. It is largely by keeping
his eyes open and seizing upon such sports for crossing purposes that the
horticulturist "improves" the plants with which he deals. How these sports
or _mutations_ come about we can now surmise. They must owe their origin to
a disturbance in the processes of cell division through which the gametes
originate. At some stage or other the normal equal distribution of the
various factors is upset, and some of the gametes receive a factor less
than others. From the union of two such gametes, provided that they are
still capable of fertilisation, comes the zygote which in course of growth
develops the new character.

Why these mutations arise: what leads to the surmised unequal division of
the gametes: of this we know practically nothing. Nor until we can induce
the production of mutations at will are we likely to understand the
conditions which govern their formation. Nevertheless there are already
hints scattered about the recent literature of experimental biology which
lead us to hope that we may know more of these matters in the future. {85}

In respect of the evolution of its now multitudinous varieties, the story
of the sweet pea is clear and straightforward. These have all arisen from
the wild by a process of continuous loss. Everything was there in the
beginning, and as the wild plant parted with factor after factor there came
into being the long series of derived forms. Exquisite as are the results
of civilization, it is by the degradation of the wild that they have been
brought about. How far are we justified in regarding this as a picture of
the manner in which evolution works?

There are certainly other species in which we must suppose that this is the