292 



MANUAL OP BOTANY 



The material of which the cell-wall is originally composed is 

 a mixture of cellulose with various pectic bodies. The re- 

 actions by which cellulose may be recognised are — 



1. It is insoluble in water, weak acids or alkalies, alcohol, 

 ether, benzol or other aromatic liquid, but dissolves in ammo- 

 niacal solution of oxide of copper (Schweizer's reagent). 



2. It is permeable by water, extensible and elastic. 



3. It swells up and slowly dissolves when treated with strong 

 sulphuric acid. 



4. It stains violet when treated with sulphuric acid and 

 iodine, or with a solution of iodine in potassic iodide and 

 chloride of zinc. 



5. It is doubly refractive when viewed with polarised 

 light. 



The pectic bodies, chiefly consisting of pectose, pectin, and 



ITlG. 640. 



Fig. 641. 



Fig. 642, 



^y* — 



Fi(j. 6d0. Bast cell of Ephedra with crystals embedded in 



tliewall. Fig.MX. Gystolith f rom Prtrie^aria officinalis. 



Fig 642. Cystolitli from the leaf of Ficus elastica. ep. 

 Three-layered epidermis, pa, ParencbsTna of leaf. cys. 

 Cystolitli. 



pectic acids, are not soluble in Schweizer's reagent, but are 

 readily affected by the action of acids and alkahes. They do not 

 stain violet with iodine, either alone or in conjvmction with 

 sulphuric acid or chlorides of the heavy metals. 



The cell-wall seldom remains simple ; soon after forma- 

 tion changes occur in it, admixture of mineral substances to 

 a considerable extent often rapidly taking place. The chief of 

 these are salts of calcium, usually the oxalate, but often the 

 carbonate. Some ceU-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 Ephedra, and others {fig. 



