52 THE VEGETABLE CELL IN GENEKAL. 



is present. Usually all the grape-sugar is extracted in a day 

 or two. 



2. The sugars. Grape-sugar has been just referred to as 

 giving the same reaction as dextrin with Trommer's test. Its 

 formula is C H 12 O C . Cane-sugar, which has the formula C^H^On, 

 gives no red precipitate with the same test, but the liquid in the 

 cells becomes bright blue, and quickly diffuses into the potassa. 1 



185. Crystals are of such general occurrence in widely differ- 

 ent orders of the higher plants, that there are perhaps none 

 in which they may not be detected. They have been found in 

 nearly all parts of the vegetable structure, more commonly in 

 the interior of parenchyma cells, sometimes in specialized crys- 

 tal-receptacles, occasionall}' in the very substance of the cell- 

 wall. The}' occur either singly or in groups ; either separate or 

 barely coherent, or in various degrees of combination. 



When solitary and simple the}' are usuall}- octahedra or 

 prisms, and their aggregations are combinations of these. Good 

 octahedral crystals are afforded by the petioles of Begonia; 

 examples of the prismatic form are found in the outer scales of 

 onions, in orange leaves, in the inner bark of maples and apple- 

 trees, and in most of the tissues of Iris and its allies. 



When the prisms are very long and slender their angles and 

 faces are seldom well defined. 2 Indeed, the most attenuated 

 forms are usually terete, or slightly flattened, and taper gradually 

 to a point at botli ends. To these De Candolle long ago gave 

 the name Raphides, that is, needles. 8 These are generally 

 massed in a compact bundle, like a wheat-sheaf, occupying a 

 large part of the interior of the containing cell. 



Raphides are by no means of such general occurrence as 

 are ordinary c^-stals, but (as Gulliver has pointed out) are 

 seemingly restricted to certain orders. 4 They are universal in 

 Araceaj and Onagracese. In the common Arums and Callas, 

 raphides-bearing cells may readily be found in the parenchyma 



1 Pringsheim's Jahrb., iii. p. 187. In the Sitzungsber. d. k. Akad. Wien, 

 for 1 859, Sachs has given colored figures illustrative of these reactions. 



2 When the longer prisms are clearly denned, they are referable to the mono- 

 clinic system. Measurements of angles are given by Holzner, in Flora, 1864, 

 p. 292. A paper by Bailey (Am. Journ. of Sc. and Arts, vol. xlviii., 1845, 

 p. 17) also contains determinations. 



* Organographie, 1827, p. 125. 



* Gulliver has examined representative plants of all the more inijwrtant 

 orders of the British Flora, with respect to the occurrence of diagnostic crys- 

 tals (Annals and Magazine of Natural History, 1863 to 1867). 



