73. 



after, the midrib region expanded and in straightening 



forced the two ends in opposite directions resulting thus 



in the expanded shape of the normal leaf under moist 



conditions.By this means it was possible to actually 



measure the cells in the curled state and then again 



of the same leaf in the expanded state, When the sections 



were fully expanded ,a number of cells in each of the 



three different tissue layers in the different regions 



of the leaf were again measured, precisely as in the case 



of the curled section^The results obtained from measuring 



the dimensions of the cells in both conditions are 



tabulated in Table VII, It is evident from the data thd/:. 



all the cells of the leaf do not increase in size equally 



when water is introduced,Tlie cells of the upper epidermis 



above the midrib increase about tv/ice as much in width as those 



of the epidermis on the lower side of the midrib, Tlie increase 



of the cells near the margin in the upper epidermis is slightly 



less than in the lov/er epidermis; while the epidermal cells 



in the region between the margin and the midrib of both the 



upper EJid lower sides show a considerable increase, though the 



cells of the upper side increased su^bout a third more than 



those of the lower side, It will be noted that the greatest 



increase takes place in the width of the cells of both of these 



tissues; the increase in length id decidedly smaller and is 



practically alike in both tissues, In the palisade tissue the 



greatest increase in length and width occurs in the region 

 betv/een the midrib and the ma,rgin, while the smallest increase 



