PLANT PROPAGATION 119 



way that they can best adapt themselves to their surroundings. 

 Let us see, for instance, why certain weeds like the dandelion are 

 so common a nuisance on our lawns. In the first place these 

 weeds have fleshy roots that reach deep down into the soil, thus 

 helping the plant to get and keep a stock of moisture and food. 

 In the second place the reserve supply of nutrition stored in 

 these roots enables the plants to put forth leaves and flowers in 

 early spring, and so to get a good start ahead of their .com- 

 petitors. Again, their short stems and tough leaves can be 

 trampled upon without killing the plant. Insects and fungous 

 diseases, for some reason, do not seem to attack them. And 

 finally dandelions produce a large number of tiny seed-like 

 fruits, each one of which is provided with a delicate tuft of hair 

 which a puff of wind will carry for a considerable distance, thus 

 insuring a wide dispersal of its seeds. In nature, then, plants like 

 the dandelion, pigweed, and thistle have survived in the struggle 

 for existence, because they are best fitted to their surroundings. 



V. THE IMPROVEMENT OF PLANTS BY MAN 



130. Artificial selection of favorable variations. In the pre- 

 ceding pages attention was frequently called to the fact that plants 

 show a tendency to vary more or less from each other. Now it 

 has been found that in a state of cultivation this tendency becomes 

 even more pronounced. A .watchful farmer will often find that in 

 his cornfield one group of individuals ripens sooner than the rest, 

 and so if he wishes to sell earlier corn, he selects and plants next year 

 corn grains derived from plants that have varied in this direction. 

 Again, he may notice that the ears on certain stalks are larger and 

 ripen more kernels (see Fig. 52) ; these the crop-raiser who uses his 

 brains would select for seed in order to increase his yield per acre. 

 Variations in many other directions might be chosen by the success- 

 ful farmer which would add immensely to the value of his crops. 

 It is estimated that if every farmer were to select his seed carefully, 

 the corn production in the United States, which at present is about 

 $1,000,000,000, in a short time would be increased 10 per cent, which 

 would add $100,000,000 to our annual income. 



