746 BIOLOGICAL EFFECTS OF RADIATION 



close to those out of doors. The optimum light intensity for production 

 of dry matter increased with the increasing age of the plant. Maximum 

 dry weight of the fruit always occurred in full sunlight. The optimum 

 intensities for growth are considerably above those given by 

 Lubimenko. 



Rose (85), used the Combes frames, covered to supply intensities 

 from 11 to 100 per cent, as measured by the Roscoe-Bunsen photometer. 

 A decrease in light intensity stimulated leaf development at the expense 

 of root development. He assumed that the optimum light intensity was 

 that value at which maximum leaf area developed; however, maximum 

 dry weight occurred at a light value considerably higher. Rose tested 

 the rate of photosynthesis of leaves developed under different light 

 intensities. Garden peas showed maximum assimilation, per unit leaf 

 weight, under full sunlight, whereas for Teucrium there seemed to be no 

 appreciable increase in the rate of photosynthesis from plants grown and 

 tested under 34 per cent light to those grown and tested in full sunlight. 

 However, it should be noted that a gram of leaves, developed in full 

 sunlight, has much less area than a gram developed in reduced light. 

 He found that leaves developed at one-half to two-thirds of full sunlight 

 could at certain stages of development assimilate carbon dioxide in full 

 daylight faster than leaves developed in full daylight. But leaves 

 developed in full daylight cannot assimilate in reduced light as fast as 

 those developed in reduced light. Shade plants exhibited a greater 

 range in morphological structure and in chlorophyll content of leaves 

 when developed under varying conditions of light intensity than peas or 

 other sun plants. With increasing light intensity a marked increase in 

 the percentage of dry matter occurred. At 34 per cent light the dry 

 matter was 18 per cent, at 100 per cent light the dry matter was 30 per 

 cent. The root weight in percentage of total plant weight increased 

 from 9 at 34 per cent light to 29 at 100 per cent light. 



Growing various plants under shades in Louisiana, Shantz (93) found 

 that potatoes, cotton, lettuce, and radishes increased in fresh weight as 

 the light intensity was decreased from 100 to 50 per cent of full sunlight. 

 None of the plants used was able to grow past the seedling stage in 6 per 

 cent light. 



Hasselbring (47), in Cuba, grew tobacco plants under light cheese 

 cloth shades which transmitted approximately two-thirds of the light. 

 The humidity was higher under the shades, evaporation considerably 

 less, and the amount of water transpired was 30 per cent less. The leaf 

 area was considerably greater under the shades, while fruit development 

 was better in the open. From the standpoint of tobacco growers, shading 

 was decidedly beneficial. 



Growing soy beans under shade at Washington, D. C, Garner and 

 Allard (37) found that the shading caused a decrease in the dry weight of 



