CHAPTER IV 



BARKS 



Barks are all obtained from dicotyledonous plants. In 

 studying barks there should be ascertained the thickness, ar- 

 rangement, form, structure, color, and cell contents of the cells 

 occurring in the outer, middle, and inner barks. 



The outer bark includes the cork cells and the phellogen 

 layer. The middle bark includes all the cells occurring between 

 the phellogen layer and the beginning of the medullary rays. 

 The inner bark includes the medullary ray cells and all cells 

 associated with them. The plan of structure of all barks is 

 similar, .but in each species of plant the structure of the bark 

 is uniform and characteristic for the species. 



A great number of drugs consist of the bark of woody plants ; 

 for this reason the bark is considered in a separate chapter from 

 the stem. 



WHITE PINE BARK 



The cross-section of white pine bark (Plate 103) has the 

 following structure: 



Outer Bark, The periderm consists of several layers of 

 reddish-brown cork cells (1) which are narrow, elongated, and 

 with thin walls. 



Middle Bark. The cells forming the middle bark are paren- 

 chyma and secretion cells. 



The parenchyma cells vary greatly in size, form, and thick- 

 ness of the walls. The cells beneath the cork cells and around 

 the secretion cells are tangentially elongated and oval in shape, 

 while the other parenchyma cells are more irregular in shape. 



The secretion cells are arranged around the schizogenous 

 secretion cavities. The cells are tangentially elongated, and the 

 walls, which are slightly papillate, are white. 



Inner Bark. The cells forming the inner bark are medullary 

 rays, parenchyma, sieve cells, and storage cavities. 



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