71. 



a cross section respectively of a curled leaf and of am 

 expanded one, Both of these sections come from the same 

 regioniof corresponding pinnae, and the same magnification 

 is used for Taoth, 



Whether the loss and gain of water by the leaf is entirely 

 an osmotic phenomenon or is accomplished partly or entirely 

 only "by imbihition might be sinswered by a measurement of the 

 cells of the leaf in the curled condition and of those of 

 the leaf in the expanded condition, Parai'fin sections of 

 curled leaves were mounted on slides, the paraffin dissolved 

 off by xylol and the preparation covered v/ith a cover slip. 

 In this manner, v/hile the sections were still in xylol under 

 the cover glass, individuals? cells picked at random in three 

 different regions of the upper and lower epidermis and in the 

 palisade tissue were measured in width and length, The two 

 dimensions of a niunber of cells of each region of a given 

 tissue v/ere then averaged and ths se were regarded as the 

 dimensions of a typical cell of the curled leaf, After the 

 measurements were obtained , the xylol was drawn out from 

 beneath the cover slip and replaced by absolute alcohol 

 while the sections were still under observation under 

 the microscope, When all the alcohol was drawn out water was 

 introduced at one edge of the cover glassiand its effect 

 on the cross section of the curled leaf noted. As soon as the 

 water came in contact with the cell wall of the cells in the 

 section, the cells began to swell and to expand so that at first 

 a vertical straightening of both endS/.^took place and shortly 



