Ch. IV, 13] ECONOMICS OF STEMS 205 



A very close relation exists between monstrosities, and 

 those extreme variations called in horticulture sports. 

 In fact a sport, the foundation of some of our most valuable 

 varieties of cultivated plants, as typified, for example, by the 

 Navel Orange, is probably nothing other than a monstrosity 

 which has originated from internal and not external causes, 

 and which can be propagated. 



Monstrosities occur, of course, in the other plant parts, 

 notably flowers and fruits, and along with our description 

 thereof we shall consider still further their causes. 



13. The Economics, and Treatment in Cultivation, of 



Stems 



As with other plant parts, stems possess structures and 

 contain substances suited to their functions and habits. 

 These materials, however, happen to meet certain needs of 

 man, who accordingly appropriates them for his purposes. 



The size, composition, and tough grain of the great 

 trunks built by trees for support of their foliage fit them ad- 

 mirably for innumerable domestic and manufacturing utili- 

 ties. Nature has supplied lumber and cabinet woods in 

 great abundance and variety, but not so great as man's 

 increasing needs; and he is driven perforce to conserve, 

 augment, and improve the supply through scientific forestry. 



Likewise from stems he obtains material for paper, not now 

 as in old times from consolidated strips of herbaceous pith 

 (papyrus), but from cellulose fibers (rag or linen papers), 

 and from the lignified elements of the xylem. These he sep- 

 arates by grinding, or else by use of chemicals which dissolve 

 the middle lamellae (page 147), and then felts them together 

 to a pulp which is compressed between rollers to the familiar 

 thin sheets. Also he uses tough bast fibers for threads, 

 notably in case of Flax, which he weaves to cloth, giving 

 linen, though cotton has a very different origin, as will 

 later appear. Both bast fibers and sclerenchyma strands 



