THE EVOLUTION OF SPECIES 205 
Then comes a period, relatively short, when, under the 
stimulation, perhaps, of changing environment, the plant 
loses its balance and begins to produce offspring unlike 
itself. Variations occur suddenly in many directions ; 
some are useful, others are not. Each form, however, is 
constant, and, if hybridization does not interfere, breeds 
true to seed. These new forms, or mutants, arising from 
a parent-plant during a period of mutation, are called by 
De Vries elementary species. The fate of these elementary 
species must be decided by Natural Selection. Those 
that are adapted to the environment will flourish and 
multiply, those that are not will perish. Natural Selection 
is the sieve through which they all must pass. 
The value of these rival theories must be tested by 
experience. There is little to guide us at present, but 
such evidence as we possess seems to be in favour of the 
mutation theory. In the first place, it explains the absence 
in Nature of transitional forms, and it does not involve 
the supposition that acquired characters may be trans- 
mitted. At the same time it alters the position that 
Natural Selection, the theory of the survival of the fittest, 
has occupied in the Darwinian theory. In the latter it 
plays the first part ; in the former it plays only a secondary 
part, sifting out from among the variations produced those 
which are of importance to the race for perpetuation. 
Last of all, De Vries has discovered one plant, a species 
of evening-primrose—M@nothera Lamarckiana—actually 
in a state of mutation, throwing off a number of ele- 
mentary species. The Irish yews are all derived from 
one plant in Ireland which was a mutation of the 
common yew, and all the copper-beeches in cultivation 
are derived from two or three sports which have arisen 
independently in several localities in Europe. The peach 
is regarded as a mutation of the almond, and the nectarine 
is undoubtedly a mutation of the peach. 
The one conclusion which we can draw from the 
Evolution theory, however stated, is, shortly, this : that 
the present vegetable forms have been derived by modifi- 
cation or amplification from pre-existing forms, and that 
there has been no break in the development of the vegeta- 
tion under the control of natural laws from the earliest 
times to the present. We look upon the vegetation as a 
great family of more or less related forms having a con- 
