SOLANACE^ 



573 



4. External medulla. 



5. Internal medulla. 



According to Coudon and Boussard, these zones (except- 

 ing vascular ring) are proportioned (by volume) as follows: 



Skin (average of two varieties) 



Cortex (average of two varieties) 



External medulla (average of five varieties) . . . 

 Internal medulla (average of five varieties) . .. . 



Per cent. 



8.79 

 36.19 



.34-17 

 14-95 



-peridefm 



outer 



cortex 



jnrter 

 cortex 



Fig. 237. — Microscopic section through the "skin" and portion of cortex of 

 potato (Solanum tuberosum). 



For consideration here, these zones are classified as fol- 

 lows: 



1. Periderm or skin. 



2. Vascular ring. 



3. Parenchyma. 



(a) Cortex. 



1. External. 



2. Internal. 



(b) Medulla. 



1. External. 



2. Internal. 



