164 PLANT ORGANS OR PARTS OF PLANTS. 



Some are almost completely lignified, while others are 

 only slightly thickened, most of them are irregularly 

 Spherical to quadratic, slightly tangentially elongated 

 (differing from the Ceylon), and richly pored; the pores 

 are simple, and are usually intricately branched, especially 

 in the more highly lignified cells. A number of the stone 

 cells are irregularly thickened, one side remaining quite 

 thin. This is the inner side, near the cambium. This 

 is an important character in cassia bark, though it is not 

 absolutely diagnostic of the bark, as has been stated by 

 some observers. The stone cells vary in diameter from 

 10 or 15 to 30 or 40, and sometimes 100 microns. Some- 

 times stone cells may be found in which starch grains are 

 deposited. 



Cork cells are not in abundance, as most of them have 

 been scraped from the bark, yet they are always present 

 in small quantities. They form the characteristic small 

 reddish-brown cell masses, distributed through the 

 powder. Isolated cork cells with slightly thickened 

 walls are present, and also typical stone cork cells. These 

 latter are quite characteristic. They average about 20 

 to 30 microns, and have partially lignified walls, with 

 straight, simple pores. The lumen is usually filled with 

 dark, reddish-brown masses. The parenchyma tic tissue 

 is apt to be irregular, contorted, slightly elongated in the 

 direction of the long axis of the twig. The walls are 

 usually stained a light yellow to deeper brown from the oil 

 which is abundant in the bark. These cells are especially 

 rich in starch, more particularly in the middle bark. 

 They average about 50 to 100 microns in diameter. The 

 parenchyma tic cells of the inner (phloem) part of the 

 bark are usually smaller than those outside. 



Fibres are conspicuous elements. Two types may be 

 distinguished. Those of the primary bark (middle bark 

 of the pharmacognosist) are in groups, and in the powder 

 are apt to be associated in bundles of 5 or 6 or more. 



