THE PLASTIC CABBAGE 149 
which these forms have attained, have resulted in the 
cultivated flora of a country like England being, so far 
as the higher plants are concerned, much larger than 
the native flora, even when all the plants which are 
grown under glass are left out of consideration. 
In the case of plants of economic importance, the 
usual aim of selection has been increase of size or 
productiveness of the parts which are useful. In some 
instances selection has taken several directions inside 
the limits of a single species, as in the forms of 
Cabbage, which are all the offspring of Brassica 
oleracea (Fig. 25), a seaside plant of Western and 
Southern Europe, and are mostly creations of com- 
paratively recent date. The Cauliflower has been pro- 
duced byincreasing the size of the inflorescence ; White 
Cabbage by promoting leaf production; Brussels 
Sprouts by encouraging the development of axillary 
shoots; while a form with a tall and woody stem is 
made into walking sticks. More often we find a 
species developed along a single line. For instance, 
the tendency to store food materials in a fleshy tap- 
root has been developed in the case of Turnip, Beet, 
Carrot; the fleshy scale-leaves which form bulbs have 
been exploited in the case of the Onion; increased 
stem-growth is promoted in Asparagus; increased 
leaf-growth in Spinach and Lettuce; while by the 
development of seeds and fruits of many kinds 
artificial selection has supplied us with the foods on 
which the human race mainly subsists. The most 
important of all these last are, of course, the different 
grains, which are the seeds of grasses of various 
genera—T riticum (Wheat), Hordeum (Barley), Secale 
(Rye), Avena (Oat), Panicum (Millet), Oryza (Rice), 
