70 



ESSENTIALS OF VEGETABLE PHARMACOGNOSY. 



ing state between successive seasons of 

 growth. In the latter ease it nndergoes 

 special modifications (Figs. 368, 371 and 

 372b). Its outer leaves become developed 

 previous to the resting stage, but not as 

 foliage leaves. They become modified in- 

 stead in various directions as to form, 

 proportions, relative position, appendages 

 and exudations, to fulfil the office of pro- 

 tection as scales, and they subsequently 

 fall away, never developing into foliage 

 leaves. When no such provision is made 

 the bud is commonly destroyed, with 

 more or less of the young stem tip near it, 

 during the resting period. Occasionally 

 the bud is protected for a time by a spe- 

 cial covering, formed by the petiole of the 

 subtending leaf. It is then called a Sub- 

 petiolar Bud. 



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THE BARK. 



Viewed from the standpoint of pharma- 

 cognosy, the bark, especially when de- 

 tached from the remainder of the root or 

 stem, is one of the most important por- 

 tions of the plant. As has been seen, it is 

 not a simple structure, but develops in 

 part from the plerom, as well as from the 

 periblem, and bears frequently, although 

 this is not true of any detached medicinal 

 bark, the epidermis as well. 



In practice the bark is commonly dif- 

 ferentiated into three layers; the Endo- 

 phloeum, that portion resulting from the 

 plerom; the Mesophloeum, the primary 

 cortex, or the products of a phellogen de- 

 veloping external to the endophloeum, or 

 both when they exist together; and the 

 Exophloeum, consisting of a primary 

 periderm. If, as is not the case in any 

 medicinal bark, the epidermis persist, it 

 will form the exophloeum. It has already 

 been made sufllciently clear that a bark 



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