320 AMERICAN JOURNAL OF BOTANY [Vol. 9. 



the plants. This limited the amount of food available for growth, and as a 

 result of checked growth smaller quantities of inorganic nutrients were used. 

 The total has expressed as percentage of dry weight was only about four 

 percent less (ratio, light to shade = loo : 96.3) in the shaded plants. 

 Expressed as percentage of green weight the ash was about twelve 

 percent less (ratio, light to shade = 100 : 87.9) in the shaded than in the un- 

 shaded plants. 



The total transpiration per culture for the period of five weeks was 833 

 cubic centimeters in the unshaded as compared with 400 cubic centimeters 

 in the shaded cultures. The water requirement, contrary to the common 

 idea that this always increases under conditions favoring high transpira- 

 tion, decreased from 672 in the shaded cultures to 546 in the unshaded cul- 

 tures which actually transpired more than twice as much as the shaded 

 plants. The amount of water transpired per gram of ash was considerably 

 less in the unshaded plants than in the shaded ones. This is just the oppo- 

 site of the results obtained when transpiration was doubled by decreasing 

 the atmospheric humidity, which doubled both the water requirement and 

 the water used per gram of ash (table i). 



These data agree with those of Schloessing (1869) who found that a 

 tobacco plant grown under a shaded bell jar had a smaller total ash content 

 and a smaller dry weight than plants grown in the open. When the plant 

 was shaded,, not only was transpiration reduced, but the amount of avail- 

 able food was also limited, growth was checked, and the plant utilized 

 smaller quantities of inorganic nutrients. Hasselbring (1914 a) did not 

 find a reduction in total ash content or dry matter by shading tobacco 

 plants. It is probable that light was not reduced enough to become a limit- 

 ing factor for tobacco plants under the conditions of his experiment in Cuba. 

 His shaded plants were much larger than those grown in the open, and per- 

 haps the increased photosynthetic area was enough to offset any reduction 

 in the rate of photosynthesis due to shading. In the experiment reported 

 here light was a limiting factor. 



The data presented in table 2 show that, when transpiration was re- 

 duced by shading, the total ash content was also reduced. This might lead 

 one to infer that there exists a relation between transpiration and the ab- 

 sorption of salts. It must be remembered, however, that, when transpira- 

 tion was reduced by shading, the photosynthetic activity was also reduced 

 at the same time, as is shown by the fact that both green and dry weights 

 of the shaded plants' were less than one half as great as those of the plants 

 that were not shaded. If checking the transpiration alone were responsible 

 for the reduced ash absorption, then the results of the dry-humid cultures 

 presented in table i should correspond with the results of the light-shade 

 cultures in table 2. These data show that when transpiration is reduced 

 to one half by increasing the humidity, the total dry matter and ash were 

 reduced only slightly and the water requirement and the water used per 



