404 ANIMAL BIOLOGY 



nitrogen of the atmosphere, trapped by Nitrogen-fixing Bacteria; 

 but the artificial conversion of this gaseous element into solid 

 forms suitable for fertilizers has taxed to the utmost the ingenuity 

 of chemists. Finally after years of intensive laboratory study and 

 experimentation, they have succeeded in developing industrial 

 processes for accomplishing this result, which have created an 

 enormous industry of world-wide extent and supplied agriculture 

 with a cheaper source of this indispensable nitrogenous food for 

 plants. 



Soil investigations involving the cooperation of chemist and 

 biologist lay the foundations for studies on seed planting, germina- 

 tion, and growth, which in turn lead to others on transplanting, 

 grafting, and pruning, and on pollination, hybridizing, and develop- 

 ing new varieties of plants. Nearly every cultivated plant that is 

 important for food or other purposes has been improved. The great 

 body of practical information which the human race has accumu- 

 lated from centuries of toil has been multiplied a hundred fold 

 within merely the past generation, through the intensive work of 

 investigators at Agricultural Experiment Stations, Colleges, and 

 Universities throughout the world. (Page 283.) 



But this indispensable work is only a small part of all that must 

 be accomplished. Man's conquest of the plant kingdom has hardly 

 begun, because the number of species already brought into his 

 service is insignificant in comparison with the wealth of available 

 kinds. Relatively few of about two hundred thousand known spe- 

 cies of higher plants are cultivated, and most of these in merely an 

 incidental way. There is every reason to believe that many plants 

 not as yet employed possess intrinsic value at least equal to those 

 under cultivation - " some neglected weed in the hands of a skilled 

 botanist may one day revolutionize agriculture." Furthermore, the 

 botanist must develop varieties of important plants which not 

 only afford the largest yield, but also are most resistant to unfavor- 

 able climatic conditions and to disease; the forester must develop 

 timberland both for the materials it supplies and the indirect effect 

 it has on soil erosion and on water conservation for agricultural and 

 other purposes ; the entomologist and plant pathologist must devise 

 means for holding in check destructive insects, as well as bacterial 

 and related microscopic parasites of plants. All these and others 

 must cooperate. For what does it profit us if we are robbed of our 

 crops? (Fig. 268.) 



