METAPLASM; POLARITY . 135 



called the "globoid" (Fig. 47, G). The crystalline inclusions sometimes 

 grow to bo very large. It has been thought by certain workers that 

 aleurone grains are self- perpetuating bodies with an individuality com- 

 parable to that of nuclei and certain plastids. That this view is correct 

 has been rendered very improbable by the researches of East and Hayes 

 (1911, 1915) and Emerson (1914, 1917) on the inheritance of aleurone 

 characters in maize, and also by the work of Thompson (1912), who suc- 

 ceeded in producing artificial aleurone grains in all essential respects 

 similar to those elaborated by the plant. 



Crystals occur in great variety in the differentiated cells of plants. 

 They may lie in the cytoplasm, in vacuoles, attached to or imbedded in 

 the cell wall, and even in special cells. They are usually salts of calcium, 

 calcium oxalate being especially prevalent. The bundles of needle- 

 shaped crystals known as "raphides" (Fig. 47, L) found in the leaves of a 

 number of plants are composed of the latter salt, as are also the spherical 

 aggregations called "druses," or " sphserraphides " (Fig. 47, C). The 

 curious clustered " cystoliths " of the Ficus leaf (Fig. 47, A) are made up of 

 cellulose and calcium carbonate. Crystals of silica are very abundant in 

 the thickened walls of wood cells and in many other tissues, such as the 

 outer cells of the Equisetum stem. Crystals of albumen, aside from those 

 found in aleurone grains, are frequently present in the cytoplasm of cells 

 poor in starch, as in the outer portion of the potato tuber. The leucoplast 

 of Phajus often contains a rod-shaped albumen crystal. Protein crystals 

 of various shapes are occasionally observed within the nucleus (Stock 

 1892; Zimmermann 1893). 



Cellulose is a common storage material, existing as a rule in the form 

 of laminae deposited upon the original cell wall. 



As already pointed out, the sap of vacuolated cells may contain a 

 number of differentiation products in solution. The cell sap is usually 

 slightly acid in reaction, owing to the presence or organic acids (malic, 

 formic, acetic, oxalic) and their salts. Inogranic salts are probably always 

 present. Amides, such as glutamin and asparagin, glucosides, sugars, 

 proteins, tannin, and many other substances are of frequent occurrence 

 in the cell sap of various plants. The carbohydrate inulin may be pre- 

 cipitated out of the sap by alcohol: this accounts for the presence of 

 nodules of radiating inulin crystals frequently encountered in preserved 

 material (Fig. 47, M). Rubber is present in the form of a suspension of 

 minute droplets in the cell sap of Ficus elastica and several gther plants. 

 Gutta-percha occurs in a similar state in Isonandra gutta. The cell sap 

 in such cases has a characteristic milky appearance. The cell sap is 

 often colored by red, blue, and yellow anthocyanin pigments (Wheldale 

 1916; Palladin 1918; Beauverie 1919), some of which change color when 

 the reaction of the sap is altered from acid to basic and vice versa. The 

 striking colors of flowers are due to "(I) the varying color of the sap, (2) 



