302 BOTANICAL GAZETTE [October 



assimi 



assimilatory cells by the shortest possible road, and the form of 

 cells best fitted for this rapid transportation is the elongated form. 

 Wagner (29) reported that alpine plants exposed to decreased 



did 



assimilation was more 



cing that tissue. 



form 



a strong development light is 

 him in this resoect. Stahl 



related palisade development to light. Eberdt (10) thought that 

 increase in palisade development is caused by assimilation and 



» 



transpiration working together, and that light in itself is never 

 the cause that calls forth palisade parenchyma. Vesque and 

 Viet (27) concluded from their experiments that light and dry air 

 (accelerating transpiration) result in a greater development of 

 palisade. Bonnier (2) adds temperature to these two factors. 

 Kearney (22) considers excessive transpiration accountable for 

 both increased palisade and succulency. Heinricher (20) related 

 equilateral structure to the vertical position of leaves and thought 

 it due to sunny and dry situations, dryness being secondary to 

 strong illumination, as some plants growing in damp situations 

 have equilateral leaves. 



As to conductive and mechanical elements, it has long been 

 known that they are reduced in aquatic plants, in the water leaf of 

 Proserpinaca being scarcely differentiated at all. If the supply 



limiting 

 ! more : 



but of course 



with the 



roots in the soil, its leaves in the air, the larger the plant, and 

 consequently the farther apart the roots and leaves, the more 

 complicated become the factors. Gilg (14) found in the xerophytic 

 family Restiaceae a mechanical ring of strongly thickened cells, 

 which Volkens (28) explained as related to poor water supply- 

 Haberlandt (17) thought mechanical influences, if they do not 

 pass beyond a certain limit, act on stereome as a stimulus for further 

 building it up. Kohl (23) found that in some plants grown in 

 damp air the sclerenchyma ring was entirely lost, xylem elements 



