776 General and Applied Biology 



plants and animals by the proper selection of seeds and parents has made 

 possible better offspring. The production of new kinds of animals and 

 plants has been possible by crossing or hybridization which has been 

 based upon the knowledge of heredity. The increase in the quantities 

 of animals and plants has been made possible as the result of biologic 

 investigation. Methods of controlling many parasites of plants and ani- 

 mals have been evolved by biologic investigation. Many improvements 

 in the proper cultivation and care of soils have also had their biologic 

 foundation and origin. Biology has also contributed in the prevention 

 and treatment of many plant and animal diseases. Plant and animal 

 foods have also been more perfectly preserved and more efficiently trans- 

 ported. Biology and chemistry have made it possible to use more com- 

 pletely and efficiently the by-products of animal and plant products 

 which originally were wastefuUy discarded. 



Hydroponics (hi dro -pon' iks) (Gr. hydor, water; ponos, exertion) is 

 a procedure in which plants are grown in solution cultures or sand cul- 

 tures. The solutions used in hydroponics must have the essential elements 

 required for the specific plants and in proper proportions. If, however, 

 the nutrient requirements of plants are to be ascertained experimentally, 

 the solutions may be made accordingly. Much of the information secured 

 regarding the relative importance of various elements for plant growth 

 has been secured through experiments with solution and sand cultures. 

 Commercially, the process of hydroponics has been used successfully but 

 on a large, scale would be expensive and might not warrant the extra 

 efforts and expense required. The elements which have been proved to 

 have some physiologic importance in green plants include magnesium, 

 nitrogen, sulfur, phosphorus, calcium, potassium, iron, boron, manganese, 

 zinc, and copper. The importance of various amounts of these essential 

 elements and the effects of their deficiencies are too extensive to be con- 

 sidered here. The reader is referred to texts on botany, plant physiol- 

 ogy, etc. "Water farming" or aquiculture when performed experi- 

 mentally has given much \aluable information as to plant requirements. 

 Biology has made many valuable contributions in fish propogation, oyster 

 cultivation, etc. 



II. BIOLOGY AND ITS RELATION TO FOODS, 

 CLOTHING, FURNITURE, AND FUELS 



Most of our foods, clothing, shelter, and fuels and much of our wealth 

 are all directly or indirectly influenced in some way by the proper and 

 effective application of a knowledge of biology. Most of our foods are 



