Trelease: Elongation of Banana Leave 



1919. 









' 



— • 



Leaved. 



-Tar- 



Act™.. 



Relative 



Ac.u.l. 





8a m 



Ill 



100 



iii 



« 







! 2p. m , "" 



4p. m 



P 





side of the midrib, the hinge cells apparently changing readily 

 in shape or size or both, with even slight changes in their water 

 content. The hinge cells appear to be peculiarly sensitive to 

 changes in the water content of the leaf or of the plant as a 

 whole, resulting from alterations in the relation between the 

 rate of transpiration and the rate of water absorption by the 

 roots. A water deficit, or a state of incipient drying, in a part 

 or in all of the plant tissue may be expected to follow periods 

 during which the transpiration rates have exceeded the rates 

 of absorption. While the hinge cells appear to be particularly 

 sensitive to water deficit, the water content of the plant as a 

 whole probably follows, in a general way at least, the changes 

 in water content of these cells. The results presented in Table 

 6 thus indicate that the leaves were nearly completely saturated 

 with water at 8 a. m., and that after that hour the water content 

 decreased progressively, reaching a minimum value some time 

 between 10 a. m. and 2 p. m. The time of minimum apparent 

 leaf width occurs somewhere within a period somewhat less 

 than two hours ; it may have occurred, as far as these measure- 

 ments show, at almost any time between 10 a. m. and 2 p. m., 

 although the minimum average reading was obtained at noon. 

 Whenever this minimum actually occurred in this particular 

 case, other observations on banana plants have shown that its 

 time of occurrence differs, even for the same plant, for different 

 days. This has also been found to be true in the case of the 

 coconut. It will be noted that, as would be expected, the set 

 of leaves exposed to full sunlight showed a much greater change 

 than did those that were partially shaded, thus indicating a 

 less-pronounced water deficit in the shaded leaves. By 6 p. m. 



