312 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
with nutrient solutions. His analyses of the tops show that when trans- 
piration was increased sometimes the amount of ash increased and some- 
times it decreased. Ilienkoff (1865) found no correlation between the 
quantity of water supplied and the total ash content of buckwheat plants 
the tops of which were analyzed after growing for a period of 67 days. 
Fittbogen (1873) found no significant difference in the quantity of ash 
found for a unit of water transpired by oat plants growing in soil in which 
the water varied from 20 to 60 percent of its water-holding capacity. 
Thom and Holtz (191 7) presented data that show that in general as the 
concentration of the soil solution is increased the water requirement of 
wheat and barley plants decreases as does also the quantity of water trans- 
pired per gram of ash found in the plant. Their table at the top of page 
50 shows' that the ash content in the whole plants, expressed in percentage 
of dry weight, is about the same regardless of the concentration of the nutri- 
ent solution in which they were grown, excepting in a very high concentra- 
tion which was injurious to growth. 
The effect of decreased transpiration brought about by shading has 
been worked on first by Schloessing (1869), and more recently by Hassel- 
bring (1914 a, h). Schloessing found that a tobacco plant under a shaded 
bell jar which transpired the least also possessed the smaller dry weight and 
ash content. Hasselbring, also working with tobacco plants, found, on 
the other hand, a smaller absolute amount and percentage of ash in the 
plants which transpired the most. The dry weight was practically the 
same in plants grown in the open sunlight and in the shade. He stated 
that it appears, therefore, that the absorption of salts by roots is independ- 
ent of the absorption of water, and that the transpiration stream does not 
exert an accelerating efi'ect on the entrance of salts. 
Sorauer (1880) and Wollney (1898 a, h) worked on the relation of ab- 
sorption of salts and transpiration as affected by atmospheric humidity. 
Sorauer found that pea plants growing in a dry chamber had a slightly 
greater dry weight and ash content than similar plants growing in humid 
chambers. Wollney, working with several crop plants grown in chambers 
with high, medium, and low humidity, found that in general the absolute 
green weight and dry matter was somewhat greater in the plants grown 
in the more humid atmosphere. The percentage of ash and dry matter in 
general increased slightly with the dryness of the air. Kiesselbach (19 16) 
found no distinct correlation between transpiration and the absolute quan- 
tity or percentage of ash or between the water requirement and ash found 
in corn plants grown in dry and humid greenhouses, or in different degrees 
of soil-moisture content. Curtis (1920) mentioned some unpublished data 
showing that doubling the transpiration of barley plants growing with their 
roots in nutrient solution has no tendency to increase salt absorption when 
the transpiration is increased by decreasing the atmospheric humidity. 
Several authors have compared the absorption of mineral nutrients and 
