190 AERATING SYSTEM [CH. 



have made it clear that the spongy mass (f in Fig. 123) is 

 an aerenchyma developed from a phellogen. That it also acts 



B 



FIG. 122. Jussiaea peruviana, L. A, habit drawing. The shoots are clothed with 

 aerenchyma up to the water level (s.w.). m.r., mud roots; a.r., air roots. 

 Aerenchyma occurs in both types of root. (Reduced.) B, Transverse section of 

 submerged part of a stem to show aerenchyma (a) developed from phellogen (pg). 

 The phloem (ph), normal cambium (c) and" xylem (xy] are also shown. [Adapted 

 from Schenck, H. (1889).] 



as a float is indicated by Spruce's 1 account of the plant as he 

 saw it growing in South America. He describes the buoyant 



1 Spruce, R. (1908). 



