301 THE STRUCTURE OF ECONOMIC PLANTS 



Minin (ii) and Golinska (6) suggest that the enlargement of the 

 axis does not always occur at the same level, and the former main- 



—xy par 



Fig. 151. Transection of sector of fleshy portion of hypocotyl showing secondary and 

 tertiary thickening. Secondary cambiums arising in secondary xylem parenchyma have 

 already produced tertiary phloem : ca, cambium ; ca r, secondary cambium ; co, cortex ; fh x, 

 secondary phloem; ph 3, tertiary phloem; ra, ray; xy i, secondary xylem vessels; xy par, 

 secondary xylem parenchyma. 



