26 ORGANOORAPHV. 



Fig. 47. Fiy. 48. Fig. 49. 



Fig. 47. Raphides of an Arum being discharged under the influence of 



water Fig. 48. Cystolithe, from Parietaria officinalis. After Henfrey. 



Fig. 49. Cystolitlie from the leaf of Ficus elastica. After Henfrey. 



by a kind of stalk formed of cellulose, upon which the crys- 

 tals are deposited as upon a nucleus. The crystals are also 

 found of other shapes besides the globular and clavate in these 

 Cystolithes. They always consist of oxalate of lime. 



The raphides appear to be simple chemical combinations of 

 the organic and inorganic acids and bases (commonly lime) 

 whicli are contained in the fluids of the plant. Such crystals, 

 therefore, vary in composition, those of most frequent occur- 

 rence consist of oxalate of lime, as in Rhubarb root. The 

 acicular raphides are also said by some observers to be com- 

 posed of oxalate of lime, Avhile others state them to be phosphate 

 of lime; their composition may possibly vary in difterent plants. 

 Carbonate of lime crystals also frequently occur in ])lants, as 

 in many of tlic CactacejE. Crystals of tartrate of lime are 

 found in the old stems of some Cuctacea^ ; those of sulphate of 

 lime in the Musaceai; and those of other composition occasionally 

 occur. 



Raphides, as might be supposed from their varying composi- 

 tion, assume different crystalline forms. Some are acicular or 

 needlc-sliai)ed, (as we have already seen,) with pyramidal ends ; 

 others, as those of oxalate of lime, crystallize in octahedra and 

 in right-angled fuur-sided prisms. Carbonate of lime crys- 

 tals assume a number of forms, but most commonly tliat of 

 tlie rliomboliedron. Other crystals with a different coniposi- 

 tion assume a variety of forms, which it is not necessary for us 

 to allude to. 



Section 2. Of the Kinds of Cells and their Connexion 



WITH EACH OTUEU. 



We have already seen that when cells arc of such forms 

 that combined together they merely come in contact without 



