THE FUNDAMENTAL SYSTEM. 



127 



(&) Ordinary herbaceous Dicotyledons furnish the beat examples of 

 fully developed fundamental tissues ; they can be most easily exam- 

 ined after soaking for some time in alcohol. 



(e) Examples of thin-walled cork are, of course, best obtained from 



Fig. 113. Transverse section through a lenticel of Betula alba, e, e, epidermis ; , 

 old stoma ; under this is a mass of cork which develops from the phellogen layer 

 lying next to the ordinary parenchyma (figured darker) ; the great multiplication of 

 cork-cells has pushed out the epidermis. X 280. After De Bary. 



the ordinary commercial article ; the thick-walled form may be obtained 

 from the bark of the beech, willow, prickly ash (Xanthoxylum Amer- 

 icanum), Viburnum opulus, etc. Its development may be observed by 

 making successive sections of the shoots at different heights. 



