SECTION 16.] 



CELL-CONTENTS. 



137 



tuber. When the potato sprouts, the starch in the vicinity of developmg 



buds or eyes is changed back again, first into mucilaginous dextrine, then 



into sugar, dissolved 



in the sap, and in this 



form it is made to 



flow to the growing 



parts, where it is laid 



down into cellulose 



or cell-wall. 



421. Besides these cell-contents which are in obvious and essential rela- 

 tion to nutrition, there are others the use of which is problematical. Of 

 such the commonest are 



422. Crystals. These when slender or needle-shaped are called 

 Rhaphides. They are of inorganic matter, usually of oxalate or phosphate 

 or sulphate of lime. Some, at least of the latter, may be direct crystalliza- 



tions of what is taken in dissolved in the water absorbed, but others must 

 be the result of some elaboration in the plant. Some plants have hardly 

 any ; others abound in them, especially in the foliage and bark. In Locustr 

 bark almost every cell holds a crystal ; so that in a square inch not thicker 

 than writing-paper there may be over a million and a half of them. When 



Pig. 462. Some magnified starch-grains, in two cells of a potato. 463. Some 

 cells of the albumen or floury part of Indian Com, filled with starch-grains. 



Fig. 464. Pour cells from dried Onion-peel, each holding a crystal of different 

 shape, one of them twinned. 465. Some cells from stalk of Bhubarb-plant, three 

 containing chlorophyll ; two (one torn across) with rhaphides. 466. Rhaphides 

 in a cell, from Arissema, with small cells surrounding. 467. Prismatic crystals 

 from the bark of Hickory. 468. Glomerate crystal in a cell, from Beet-root. 

 469. A few cells of Locust-bark, a crystal in each. 470. A detached cell, with 

 rhaphides being forced out, as happens when put in water. 



