26 



MASS. EXPERIMENT STATION BULLETIN 183. 



chj-ma. Except under the stomates, where it is thicker, the chlorenchyma 

 is composed of three or four layers of cells containing around the inside 

 of the walls the green chloroplasts which give the color to the bark. Next 

 in order are the large thin-walled cells of the inner cortex, the lowermost 



EPIDERffllS 



Fig. 9. — Transection of a healthy rose stem. 



of which contain abundant starch grains in storage. Next there are 

 areas of angular, very thick-walled cells, the bast fibers. The walls are 

 so thick that there is hardly any opening (lumen) through the center. 

 In longisection these are seen to be shaped like long, sharp-pointed pencils, 

 with the sharp ends overlapping. Their function is to give rigidity and 



