THE SHAPE OF CELLS. 



543 



Figuke 2. Longitudinal section of pith of the elder, Sambucus canadensis. 

 X 220 diam. The numeral in each cell indicates the number of contacts 

 which that cell has with other cells. Two numerals on a septum indicate the 

 contacts of the cells above and below the septum. The letters are explained 

 in the text. 



