68 



BOTANY 



PART I 



able size and can be seen to belong either to the tetragonal or 

 nionosymmetrical crystal system ; or the crystals are so small and 

 numerous that their form cannot be clearly made out and they appear 

 as a crystalline sand filling the cell. Frequently they form crystal 

 AGGREGATES, clusters of crystals radiating in all directions from a 

 common centre. In the Liliaceae, Orchidaceae, and other Mono- 

 cotyledons, compact bundles of needle-shaped crystals of calcium 

 oxalate, the so-called raphides, are especially frequent (Fig. 71). 



Such crystal bundles are always enclosed in a 

 large vacuole filled with a mucilaginous sub- 

 stance. The degree of concentration of the 

 mother liquor from which the crystals have 

 separated, determines, according to Kny (^•'), 

 their form, whether tetragonal or monoclinic. 



Siliceous bodies, which are only soluble in hydro- 

 fluoric acid, are found in the cytoplasm of many cells, 

 especially of Palms and Orchids, and often completely 

 fill the whole cell. 



Tannin. — Highly refractive vacuoles filled with a 

 concentrated solution of tannin are of frequent occur- 

 rence in the cytoplasm of cortical cells, and may often 

 grow to a considerable size. The dark-blue or green 

 colour reaction obtained "on treatment with a solution 

 of ferric chloride or ferric sulphate, and the reddish- 

 brown precipitate formed with an aqueous solution of 

 potassium bichromate, are usually accepted as tests for 

 the recognition of tannin, although equally applicable 

 for a whole group of similar substances. 



Fats- and Oils in plants are mixtures of fatty-acid 

 esters. Frequently, as in most Monocotyledons, a fatty 

 oil appears in the old chlorophyll grains. The occur- 

 rence of castor oil in the form of highly refractive drops 

 in the cytoplasm of the aleurone-containing cells in the 

 Fig. 71.— Cell from the cortex endosperm of the castor-oil seeds, has already been re- 

 ef Dracimna rubra, lilled f^^.^.^^ ^^^ qj^ usually occurs in this form. But fatty 

 with mucilaginous matter , , , . ,i , , . 



an.l containing a bundle of substances may also appear in the cytoplasm as ir- 

 raphides, r. (x 100.) regularly shaped, more or less soft grains, as for 



example in the vegetable butters and in the wax of 

 various seeds ; they may even be crystalline, as in the needle-like crystals 

 of Para-nuts {Berthollctia excelsa) and of Nutmeg (Myristica fragrans). Special 

 cytoplasmic structures in which the drops of oil are embedded, are of fre- 

 quent occurrence in the epidermal cells of Orchidaceae and Liliaceae and go 

 by the name of elaioplasts. These appear to result from the fusion of oily, 

 disorganised chromatophores, and thus resemble some of the products in autumnal 

 leaves C). 



Glycogen. — This substance (**) related to starch, and of i'requcnt occurrence 

 in animal tissues, fulfils, according to Eruera {^'*), the same functions in the 

 Fungi as sugar and starch in the higher plants ; it also occurs in tlio Myxomycetes 

 and the Cyanophyceae. Cytoplasm containing glycogen is coloured a reddish- 



