92 EDITH SCHWARTZ CLEMENTS 



2. A typical xerophyll consists entirely of palisade cells with few 

 air-spaces and with or without water-storage tissue. 



3. A typical mesophyll consists of equal amounts of palisade and 

 sponge tissue, and moderate air-spaces. 



^4. Decreased light and increased water both cause an increase 

 inieaf surface and a decrease in thickness. 



' 5.; The lateral tension in the cells which causes a thinning of 

 theTleaf is due to the sensitiveness of chlorophyll to light. 



<6. In weak light the chloroplasts arrange themselves in the most 

 favorable position for the absorption of the light. 



7. The tension in the cell caused by the lateral arrangement of 

 the chloroplasts increases the horizontal axis of the cell at the ex- 

 pense of the vertical axis and gives rise to funnel, globose and oblate 

 cells. 



Ts. Decreased light causes a somewhat looser arrangement of the 

 chlorenchym cells, and especially of the palisade. 



rpx Increased water causes an increase in the transpiring surface 

 of the cells, hence looser arrangement, especially of the sponge cells, 

 and oblobateness of prolate cells. 



(JO} A woolly covering of hairs decreases the light and transpira- 

 tion for the chlorenchym tissues and hence permits looser arrange- 

 ment of the cells. 



'a i .) Increased light and decreased water both cause a reduction 

 in leaf surface and increase in thickness. 



12. In strong light the chloroplasts arrange themselves vertically 

 in order to screen against over-illumination. 



13. The vertical tension in the cell caused by the vertical posi- 

 tion of the chloroplasts increases the vertical axis of the cells at the 

 expense of the horizontal axis, and gives rise to prolate and prolo- 

 bate cells. 



414; Strong light causes a closer arrangement of the chlorenchym 

 cells, and especially of the palisade. 



15. Decreased water causes a decrease in transpiring surface and 

 hence closer arrangement of the cells, especially of the sponge, and 

 prolateness in the sponge cells. 



1 6. Humidity is closely connected with water-content, but is also 

 directly efficient in changing the cuticle. 



17. Temperature acts indirectly upon the plant through water and 

 humidity. 



