1912] DACHNOWSKI—BOG PLANTS 511 



used as an indicator, would further determine the difference and 

 variability in absorption, resistance, or tolerance. Inasmuch as 

 the amount of mineral salts in bog soils and the amount used in 

 the growth of bog plants is very small, and since the lack of larger 

 quantities is not a factor in the succession of bog associations, the 

 most fundamental distinction is that which controls the supply 

 of available water. A 



me 



com 



requirement of plants for the period of their growth would have the 

 merit of convenience, and, it must be admitted, the accuracy which 

 is often questionable in the unit employed and as preferably 

 expressed in agricultural literature. The unit of water require- 

 ment now used in agricultural texts for ten different economic 

 species is 450 pounds of water for one pound of dry matter pro- 

 duced. Data of that character do not place the classification and 

 comparison of soils, correlations with fertility or with age of plant, 

 maximum growing period, and seasons on a measurable basis. 

 The unit is numerically inaccurate and does not express the f unda- 

 mental and causal relations. 



Experiments upon the transpiration value of bog plants in 

 relation to structure and habitat, to be published later, have 

 shown that the data cannot always be expressed satisfactorily in 

 the gm 2 h system. Transpiration is a reciprocal relation. It is 

 affected by the conditions which react upon the absorbing roots, 

 and it is associated with chlorophyll activity and the absorption of 

 carbon dioxide in the vertical gradient. Transpiration in the lower, 

 more humid stratum of a bog meadow is often slight for days at a 

 time. The luxuriousness of the vegetation and the amount of 

 dry matter produced do not vary in this case with the transpiration 

 quantity, but with protoplasmic permeability and the specific 

 metabolism, permitting of exchanges by solubility, and with the 

 active enzymic agents within the cells which effect the assimilation 

 or the destruction of the substances in the external medium. 



What 



perm 



12 



lib 



spannung 



aut von Pflanzenzellen. Jena. 191 1. 



W., Zur Kenntnis der chemischen Zusammensetzung der 



Plasmamembran. Ber. Deutsch. Bot. GeseUs. 29:247-260. 1911. 



