452 MANUAL OF BOTANY 



but probably no other kind of proteid is usually present. Some, 

 however, are thought to be composed of albuminates, as they 

 dissolve only in potassie or sodic hydrate, or other alkalies. 



The aleurone grains are frequently associated in the cells of 

 the seed with either starch or oil. Occasionally both these 

 compounds are present. 



In other cases the reserves of proteid are crystalline in 

 structure. Crystals of this character are easily found in the 

 tuber of the potato, lying in the cells very near the epidermis. 

 They are also met with in the thallus of certain seaweeds. 

 Many of them can be made to crystallise from the solvents 

 which are used to extract them. 



The mode of formation of these aleurone grains is still not 

 certainly known. Some authors regard them as deposited by 

 a process something like crystallisation following the abstraction 

 of water from the cell. Others have described their formation 

 as one of secretion by the protoplasm. The latter view seems 

 the more probable one. 



Fats or oils occur copiously in certain seeds, such as those 

 of the castor-oil plant {Bicinus communis), the Brazil-nut 

 (BertJioUetia excelsa) and others. They are found also in the 

 cells of the floral leaves of many plants, and in many fruits. 

 They are probably formed by the protoplasm, originating in 

 small droplets in its meshes, which as the fat accumulates run 

 together, till the cell is saturated with it. In some plants 

 certain plastids have been described as forming oil, much as the 

 leucoplasts do the starch grains. These bodies have been called 

 elamplasts. 



Other reserve materials are known which are not so wide- 

 spread as those already described. Such are the glucosides 

 found in many of the Eosacese, the Cruciferae, and allied orders. 

 These are bodies which when decomposed give rise to a sugar, 

 and various other bodies usuall}^ belonging to the so-called 

 aromatic compounds. Amygdalin, found in the Cherry Laurel 

 (Pnvnus Laurocerasus), may be mentioned as an example. 

 When split up by chemical means, it gives rise to sugar, 

 benzoic aldehyde, and hydrocyanic acid. 



All these bodies, when acted upon by a process analogous to 

 the digestion known in the animal kingdom, are converted into 

 materials which can directly nourish the living substance, or 

 can be transported easily about the plant in a condition of which 

 the latter can readily take advantage, needing indeed very little 

 constructive change to fit it for actual assimilation. 



