SEED AND ROOT 



189 



roots. The slender-stemmed plant, which is often top-heavy with its 

 massive crown of leaves, derives welcome support from this very curious 

 arrangement. 



As incidental reference has just been made to aerial roots, perhaps this 

 is the most fitting place to offer what little we have to say about those 

 interesting organs. 



Plants which grow within the inter-tropical regions show a very 

 conspicuous tendency to develop roots above-ground ; and the phenomenon 

 is not confined to one family or order, but has been observed in plants very 

 far removed from one another in the system of Nature. Moreover, the 

 objects for which such roots are produced may vary greatly. Thus, some 

 roots (like those of the Pandanus-trees just mentioned) answer the purpose 

 of supports. The Paxiuba (Iriartea), a tall, erect, smooth-stemmed Palm 

 with a large crown of curiously cut leaves, found in the Amazon region, is 

 remarkable on this account. " Its great singularity," says Dr. Wallace, " is 

 that the greater part of its roots are above-ground, and they successively 

 die away, fresh ones springing out of the stem higher up, so that the whole 

 tree is supported on three or four stout straight roots, sometimes so high 

 that a person can stand between them 

 with the lofty tree growing over his 

 head. The main-roots often diverge 

 again before they reach the ground, 

 each into three or more smaller ones, 

 not an inch each in diameter. Though 

 the stem of the tree is quite smooth, 

 the roots are thickly covered with large 

 tuberculous prickles. Numbers of small 

 trees of a few feet high grow all around, 

 each standing on spreading legs, a 

 miniature copy of its parent." 



Then there are feeding aerial roots. 

 A large number of tropical Orchids, 

 epiphytic on old trees, besides possess- 

 ing naked air-roots which subserve the 

 purpose of attachment, have others 

 which are modified for the absorption 

 of nutriment from the surrounding 

 atmosphere indeed, in a few cases 

 the Orchid has no green leaves (e.g. 

 Polyrhiza) ; the roots do everything. 

 These modified roots hang down from 

 the stem or branch of the tree to 

 which the plant is anchored, in white 

 thread-like bunches, the whiteness 



Photo by] 



FIG. 241. PINE CONE. 



\E. Step. 



A cone of the Cluster Pine (Finns pinaster), a tree 



that has been of great value in reclaiming land from 



the sea. One-half the natural size. 



