30 BOTANY PART i 



(b) Vaeuoles containing Fats (Fatty Oils). These substances are 

 of common occurrence as reserve materials ; about nine-tenths of all 

 Phanerogams store them in their seeds. In seeds especially rich in 

 oil this forms highly refractive droplets distributed through the 

 cytoplasm (e.g. castor-oil in seeds of Ricinus) and may form 70 / Q 

 of the dry weight. Fats are glycerine esters of fatty acids, especially 

 of palmitic acid (C 16 H 32 2 ), stearic acid (C 18 H 86 O 2 ), and oleic acid 

 (C 18 H 34 2 ). Since fats provide a greater amount of energy than 

 other storage substances, the space available is best utilised for them. 



(c) Vacuoles with Ethereal Oils and Resins ( 27 ). These also occur as highly 

 refractive droplets. They are found in the cells of many petals. Special cells, 

 often with corky walls and filled with resin or ethereal oils, are found in the 

 rhizomes of certain plants, as for instance in those of Acorus Calamus and of 

 Ginger (Zingiber officinale) ; also in the bark, as, for example, of Cinnamon trees 

 (Cimiamomum) ; in the leaves, as in the Sweet Bay (Laurus nobilis).; in the 

 pericarp and seed of the Pepper (Piper nigrum} ; in the pericarp of Anise (Illicium 

 anisatum}. Ethereal oils and resins have antiseptic properties. In flowers their 

 scent assists in attracting insects. Under some conditions the oil assumes the 

 crystalline form, e.g. in rose petals. 



2. Solid Inclusions of the Cytoplasm, (a) Crystals of Calcium 

 Oxalate. Few plants are devoid of such crystals. They are formed 

 in the cytoplasm as end products of metabolism, within vacuoles 

 which afterwards enlarge and sometimes almost fill the whole cell. In 

 such cases the other components of the cell become greatly reduced ; 

 the cell walls at the same time often become corky, and the whole 

 cell becomes merely a repository for the crystal. The crystals may 

 be developed singly in a cell, in which case they are of considerable 

 size (Fig. 130 k, 175 Bk, 184 k), or many minute crystals may fill the 

 cell as a crystalline sand. In other cases they form crystal aggregates 

 (Fig. 130 k, 186 k), clusters of crystals radiating in all directions from 

 a common centre, or many needle-shaped crystals lie parallel forming 

 a bundle of raphides (Fig. 22). The various types of crystals pre- 

 dominate in different plants. 



The LARGE SOLITARY CRYSTALS belong to the tetragonal or to the monosym- 

 metric system, the concentration of the mother-liquor from which they crystallise 

 out determining which system is followed. The stellate CRYSTAL AGGREGATES 

 radiating from an organic nucleus are particularly common. In Monocotyledons 

 and in many Dicotyledons RAPHIDES are of widespread occurrence (Fig. 22), the 

 bundle of crystals being always enclosed in a large vacuole filled with mucilage. 



SILICEOUS BODIES, which are only soluble in hydrofluoric acid, are found in 

 the cytoplasm of many cells, especially of Palms and Orchids, and often com- 

 pletely fill the whole cell. 



(b) Aleurone Grains. Proteid Crystals. Albuminous substances 

 may be stored in a dissolved form in the cell sap of succulent parts of 

 plants. Thus they can be precipitated by treatment with alcohol in 

 the cells of the potato tuber. In dry structures, such as many seeds, 



