370 



BRITISH FLOWERING PLANTS 



larger, and thinner, being 0'22 mm. in tliickness against 

 0'35 mm. 



Fio. 265. 



-Transverse section of a Beech leaf grown in sunshine. 

 p, jialisade layers ; s, spongy parenchyma. 



Much enlarged. 



M. de Lamartiere gives the following measurements 

 as showing the contrast between leaves exposed to the 

 sun and those growing in shade : — 



It is a remarkable fact that the roots of many trees 



are covered by an evenly 

 woven generally thin, but 

 in some cases compara- 

 tively thick layer (Fig. 

 2S7), of mycelial filaments 

 known as a mycorhiza. 

 This is not only no injury, 

 but a positive benefit to the tree. There is, indeed, 



Fig, 266. — Transverse section of a Beech 

 leaf grown in shade, p, palisade layer ; 

 i-, spongy parenchyma. 



