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PAPERS ON BOTANY 133 
the forest was much greater than that of the open dune areas, 
but in the fall visible wilting became evident in the former of 
these situations where it was found that the water had been 
reduced to the wilting coefficient. This was evidently due to 
the presence of a vegetation so abundant that its demands for 
water could not be met by the sand which holds a much 
smaller amount of available water than any other type of soil. 
Further evidence of this was noticed upon the open sand where 
there was no visible wilting at any time. Although the avail- 
able water for plant growth is always low there, the dmand 
made upon it is of course almost negligible because of the 
sparcity of plant growth. 
More rapid water loss upon the open sand as compared to 
the low rate for the forest, was quite different from the findings 
of previous investigations made upon desert plants by Bakke,* 
Livingston, and Shreve.2 These investigators report a 
very low index for the various desert xerophytes studied. In 
fact the first named author has suggested as a criterion for the 
mesophytism of a plant its foliar index of transpiration; and 
in the suggested scheme the mesophyte should show the highest 
index and the xerophyte the lowest. Intergradations in the 
scale would indicate different degrees of mesophytism. Yet 
in the work upon Tilia it was found that such an application 
would prove misleading because the transpiration current is 
very much greater in the most xerophytic habitat than in the 
established dune forest which is certainly the most mesophytic 
of the five situations, and the leaf structure in the former of 
these habitats is undoubtedly much the more xerophytic. 
It will be recognized, however, that the situation in the case 
of Tilia is different from that in the investigations of the above 
named authors. 
They were invstigating transpiration of certain xerophytes 
which were growing in their normal environments. This is 
rather an instance of a species making a rapid correlation to a 
forced environment; and although the assumed xerophytism 
Bakke, A. L. Studies on the Transpiring power of plants as indicated by 
the method of standardized hygrometrie paper. Jour. Ecol. 2: 145-173. 1914. 
* Livingston, B. E., and Shreve, Edith B. Improvements in the methods of 
determining the transpiring power of a plant surface of hygrometric paper. Pt. 
World. 19: 287-309. 1916. 
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