DISCUSSION OF PLANT INDUSTEIES 455 



possibilities of such treatment (Fig. 349). Three rows of 

 potatoes were planted side by side, the planting and cultiva- 

 tion of all being the same. The results from different kinds 

 of spraying, as shown in the legend under the figure, indi- 

 cate clearly the great importance of this treatment. If you 

 will ascertain the price of potatoes in your local market, and 

 estimate the value of the increased yield, its significance will 

 be more fully seen. It costs as much in money and labor to 

 plant and cultivate a poor crop as a good one. 



416. An artificial association of plants. By draining or irri- 

 gating, cultivating and fertilizing the soil, planting the seed 

 or plants at the right time and in the best way, caring for 

 them and fighting their diseases, a highly artificial and depend- 

 ent association of plants has been developed. Xone of these 

 plants would naturally grow alone and unmixed with other 

 plants. They have been cultivated and protected until, when 

 this cultivation and protection are discontinued, their produc- 

 tivity rapidly decreases. They would soon be unable to hold 

 then- own against the many natural plants that would begin to 

 occupy the previously cultivated region. ]Many of the charac- 

 teristics for which cultivated plants are valued, such as tender 

 stems or foliage, seedless fruits, and double flowers, tend to 

 weaken their capacity to succeed in the struggle for existence. 



III. LEADING AGRICULTURAL AXD HORTICULTURAL 



PLANTS 



417. Commercial importance of the cereals. Under the name 

 cereals are included many economic plants of the Grass family. 

 They produce grains (seeds or fruits) in which food material 

 is stored in compact form. The principal cereals named in the 

 order of their yields for the whole world, stated in tons of 

 2000 pounds, are: 



Rice . 53,500,000 



Rye . . 40,500,000 



Barley 31,000,000 



