igo6] TRANSEAUBOGS OF THE HURON RIVER VALLEY 



29 



the fact that plants grown in bog-water cultures develop normally. 

 The light conditions in the several cultures were the same, direct 

 sunlight being avoided by a cloth screen. It is evident that in this 

 case there is no response to strong light in the development of the 

 palisade tissue (49). It would seem rather to be a response called 

 forth by a reduced transpiration current (44, p. 7). As to function, 

 it may aid in the transfer of food materials as suggested by HABER- 

 LANDT (20, p. 260). 



FIG. 15. Average plants showing effect of surrounding conditions. From 

 photographs. 



This plant proved to be the most plastic of all of the species used 

 in the experimentation, and was the only one which showed marked 

 variation in the internal structures. Ecologically the results indicate 

 (i) that an undrained peat substratum may cause xerophilous struc- 

 tures, but that the effect is to be correlated with lack of aeration of 

 the substratum rather than with the acidity; (2) that the same effect 

 may be induced by lowering the substratum temperature (the air 

 temperature remaining the same), and thus impeding the rate of 



