512 BOTANICAL GAZETTE [December 



of the substances in the medium and in the plasmatic membrane 

 is prerequisite to penetration (osmosis) into the living cells. 



In previous publications on the factors by which the present 

 bog vegetation is determined the writer pointed out that different 

 species of cultivated plants show marked differences in the degree 

 of sensitiveness to the toxic conditions of a bog habitat. That the 

 stunted plants in these experiments have not lost their capacity 

 for absorption and growth can be readily demonstrated. The 

 plants resume their natural functions as soon as they are placed in 

 dilutions less fatal in its effects. In contrasting the differences 

 in physiological activity it was further shown that various phases 

 of absorption and transpiration resulted from the progressive addi- 

 tion to the medium of chemically inert filtering materials. Types 

 of soil were used ranging from the weathering products of soil- 

 forming rocks to the completely oxidized products characteristic 

 as the final residue. Incidentally it was shown that the normal 

 growth of the plants in the uncontaminated soils was replaced by 

 an abnormal retardation. In the main the study indicated that 

 upon extraction of the injurious substances by means of insoluble 



a 



adsorbing bodies, not only the differences between different species 

 as to their tolerance and resistance were less pronounced, but 

 also the differences in toxicity existing between the several zones 

 within the same habitat. The selective action of the habitat was 

 shown to be greatly diminished upon the removal of the injurious 

 organic substances accumulating in the peat substratum. The 

 conclusion was drawn that the relative power in bog plants for 

 absorbing or rejecting the injurious constituents of bog soils and 

 bog water was therefore the limiting factor, controlling the survival 

 value of invading species and of plants native to the habitat. 

 The roots of bog xerophvtes are not much shorter than those of 



the 



growth is horizontal rather than downward 

 be regarded as one due to low soil tempera 



ture or to a slight oxygen content. The inhibitory factor 

 growth which increases with depth is the reducing action of 

 stratum and the incomplete disintegration of organic com 

 It is now well known that certain root enzymes are oxidizing 



