112 



The Living Plant 



mense thickening of the cell- wall (figure 36). A conspicuous 

 case is the Ivory Palm, which has seeds so hard as to constitute 

 a substitute for ivorj'- in the making of buttons and other bijou- 

 terie, while the seed of the Date owes likewise its stony hardness 

 to the same material. Though so hard, this cellulose is easily 

 digested to sugars by the action of suitable enzymes, and the pro- 



FiG. 35. — Typical grains of a dozen different kinds of starches, highly magnified. The 

 kinds, in order of arrangement in this picture are; — 



Potato Maranta Pea Hyacinth 



Wheat Oats Sago Smilax 



Canna Corn Bean Oxalis 



cess is applied commercially to ordinary wood in the manufacture 

 of wood alcohol. Naturally, the very cells which make cellulose 

 have the power to digest it away once more where needful; and 

 this is why cell-walls, even when well grown, can become perfo- 

 rated, absorbed, split, or even re-adjusted in such a way that they 

 seem to have slid upon one another. 



