EPIDERMAL TISSUE. 



61 



cells distributed over the whole section. The stone cells can 

 easily be recognized by their structure as well as by the red 

 stain they assume with phloroglucin and hydrochloric acid. 



Fig. 40. Cassia bark, cross-section, 

 with stony parem" 

 bast fibre ; pb, a group < ^ 

 rays; u, sieve tubes (Moeller). 



!-section. K, stony cork cells ; pr, cortical parenchyma, 



; cells ; st, stone cells forming an interrupted ring ; b, 

 >f primary bast fibres ; sch, secretion cell ; m, medullary 



CHAPTER XIII. 



EPIDERMAL TISSUE. 



This tissue has already been met with in the exercise on the 

 onion epidermis, but the latter is not quite a typical example, 

 as there are no stomata or breathing pores present, which are 

 always found when an epidermis is exposed to the air. Since 

 the onion scale epidermis is not exposed to the air there is no 

 need for the pores and they are consequently absent. In other 

 respects the epidermis of other plants resembles very much that 

 of the onion. 



The tissue constitutes the primary covering of the plant. It 



