36 
THE PLANT WORLD. 
cies and varieties, are discontinuous. The gap which separates them is 
never bridged. Units may die out, leaving the gaps between neighboring 
units still wider. The problem of the mode of origin of species resolves 
itself into the question of how elementary species and varieties originate. 
Organic nature has not reached the end of its development and the origin 
of species may be observed in the origin of elementary species and varie¬ 
ties. The method of experimentation is also available. The idea of 
enormous time requirements demanded by Darwin’s hypothesis may now 
be discarded. The chief requisite is to “ try to arrange things so as to 
be present at the time when nature produces another of these rare 
changes.” 
The Origin of the Peloric Toad-flax (Linaria vulgaris peloria ).— 
Pelories are sometimes produced at the base of the raceme of the common 
variety (L. vulgaris), but the peloric variety bears only peloric flowers, 
and the form may originate independently in different localities, and since 
the peloric form is barren, there must be as many mutations as localities. 
In the experiment the mutation sought for was observed only after eight 
years of work, and this is the first experimental mutation of a normal 
into a peloric race. “ The mutation took place at once. ... No interme¬ 
diate steps were observed. . . . There was ... no visible preparation for 
the sudden leap. ... No reminiscence of the former condition remained. 
. . . Not a single flower on the mutated plant reverted to the previous 
type. . . . The whole plant departed absolutely from the old type of its 
ancestors.” The numerical proportion of the mutation was only i% of 
the whole crop of 1,750 flowering plants. This emphasizes the need of 
cultivating large groups of plants in experimental work. The experiment 
was repeated, showing the iterative nature of mutation. 
In the second generation, 90% of the pelories inherited the pelorism. 
The 10% reverting were doubtless either atavists or vicinists. 
The snapdragon ( Antirrhinum majus) produces peloric races in the 
same way as does the toad-flax. The most widespread peloric variety is 
that of Gloxinia, and several other plants are mentioned that produce 
peloric flowers. Some families are more liable to pelorism than others. 
Here is a rich field for further studies of experimental mutation. 
The Production of Double Flowers. —The historical facts concerning 
the origination of double varieties justified the attempt to obtain them 
experimentally. A species was chosen which had not been known pre¬ 
viously to produce a double variety, and success was enhanced by the 
choice of a plant the nearest relatives of which are known to have pro¬ 
duced double flowers. Such a plant was the corn-marigold ( Chrysan¬ 
themum segetum), having tubular disc flowers and an average of 13 ray 
flowers. The variety grandidorum has an average of 21 ray florets, 
and from this the double variety was finally produced. Out of 1,500 
plants 500 were chosen having 21 or more rays, but only two heads had 
as many as 22, and these on one plant. The index of doubling in the 
composites is not the increase in number of marginal ray florets, but the 
conversion of tubular disc florets into rays. Up to the fourth generation 
this character did not appear, when it suddenly manifested itself in 3 
