50 



VEGETABLE PHYSIOLOGY 



Like the substance of the middle lamella, both lignin 

 and cutin are soluble in warm nitric acid containing potassic 

 chlorate. 



In some cases the cell-wall of the epidermal protoplasts 

 is impregnated with various matters that do not proceed 

 from its own disintegration. Among these are various 

 fatty bodies, while wax is sometimes very conspicuous. 

 The bloom of such fruits as the grape and the plum is 

 composed of very line waxy particles ; the impregnation 

 in their case having been so great that certain particles 

 have passed beyond the walls and formed a layer on the 



FIG. 48. CRYSTALS OP CALCIUM 

 OXALATE IN WALL OF CELL 

 OF THE BAST OF EpJiedra. 



FIG. 49. SECTION OF PORTION 

 OF LEAF OF Ficus, SHOW- 

 ING CYSTOLITH (cijs] IN 

 LARGE CELL OF THE THREE- 

 LAYERED EPIDERMIS (<?jt?\ 



outer surface. The leaves of the wax-palm show an even 

 denser deposit. 



Mineral matters are also of frequent occurrence in the 

 cell-wall. The chief of these are salts of calcium, usually 

 the oxalate, but often the carbonate. Some cell-walls show 

 a copious deposit of regular crystals of one of these such 

 are the cells of the bulb scales of the onion, the fibres of 

 the bast of Epkedra and others (fig. 48). In many plants 

 copious deposits of silica are formed in the cell-wall, 

 especially in the epidermal cells of the Equisetacea, and in 

 those of the cereal grasses. The value of this deposit to 

 the plant is not very evident ; it appears at first sight to be 



