CONIFERALES 265 



Taxodium, when growing in its favorite swampy habitat, has 

 pecuHar vertical outgrowths from the roots, called "cypress knees," 

 extending upward so far that they are seldom covered by the water 

 (fig. 273). The base of the trunk, in swampy habitats, is often im- 



l'"iG. 270. — Cryptomeria japonica: transverse section of leaf, showing a single bundle 

 and single resin duct. The cells in which plastids are indicated are intensely green. A 

 thinner section would have shown more numerous air spaces; X155. 



mensely swollen, and may be thickly covered with short, fleshy, 

 adventitious roots (figs. 274, 275). When dry, the adventitious roots 

 and the "cypress knees" are very Hght, with xylem tracheids as thin 

 as in the wood of Ochroma, the famous "balsa" wood. 



The young root of Pinus, as it is found in a ripe seed, has about 



