This is no visionary ideal. These principles have already been 

 brought to bear in improving agricultural practices. By proper 

 selection of adapted varieties, choice of proper planting dates, and the 

 use of storage for treating planting stocks over proper periods at cor- 

 rect temperatures, it has been possible to place certain farm practices 

 on a more profitable basis. Special strains of crops such as wheat, 

 soybeans, and sugar beets have been developed for planting in specific 

 regions. The use of cold storage for holding planting stocks of po- 

 tatoes, onions and other bulbs, and seeds to improve the rate at which 

 the subsequent crop grows is standard practice. Now that the effects 

 of photoperiod are coming to be more clearly understood, there is a 

 sharper realization of the very marked effects which a difference of a 

 few hours or even minutes in the length of the period of illumination 

 each day may have upon the character and rate of growth, blooming, 

 and fruit and seed production. This means a more intelligent selection 

 and use of varieties which are photoperiodically adapted and the 

 abandonment of attempts to grow those which are not suitable. 



Controlling Length of Photoperiod 



In the cases of several crops grown especially for their flowers, either 

 in greenhouses or under field conditions, it is possible to shorten or to 

 supplement the hours of natural daylight by shading or artificial 

 illumination. Thus, in the case of chrysanthemums and some other 

 flowers, it is commercially feasible to use existent varieties and to 

 manipulate the light conditions under which they are grown so as to 

 obtain certain desired results. 



Timothy, grown in many sections of the northeastern United States 

 as a hay and pasture crop, is a long-day plant. During the shorter days 

 of the year it forms leafy rosettes, but after the cold temperatures of 

 winter and during the increasingly longer days of spring and early 

 summer the stems elongate, and the plants head out and become tall 

 and stemmy. Most commercial stocks consist of a mixture of types 

 which vary in the degree of their response to photoperiodic conditions. 

 Such a mixture produces fair yields throughout regions having a wide 

 range of prevailing photoperiods, because it is made up of seeds 

 some of which wiU develop into plants whose requirements would 

 be similar to the conditions prevailing in the specific locality 

 where they are sown. But for any given locality greater yields would 

 be obtained if a more uniform stock containing a higher percentage of 

 specially adapted seed were used. Various native species of grasses 

 likewise consist of mixtures of types which vary greatly in their re- 

 sponse to both photoperiod and temperature. Thus, certain species 

 which have extensive ranges north and south show a different pro- 

 portion of these types when the seeds are obtained from the southern 



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