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INTRODUCTION TO CYTOLOGY 



sperm and cotyledons of seeds. In the animal egg the storage material 

 commonly exists in the form of " yolk globules," or "deutoplasm spheres," 

 which consist for the most part of relatively complex protein compounds. 

 Fat or oil globules are usually present with them. In plants the most 

 characteristic storage product is starch, the origin and characters of which 

 were described in Chapter VI along with the plastids by which they are 

 formed. In some organisms, including the fungi, glycogen appears to 

 carry on the function performed by starch and sugar in the higher plants. 

 Fats and oils, usually in the form of droplets but sometimes of soft grains 

 or even crystals (nutmeg), comprise another important class of storage 

 substances : these are especially prevalent in seeds and spores, where light 

 weight is of advantage. In many cases oil may be produced anywhere in 

 the cell, but in certain forms it has been found that special elaioplasts, and 



f & 



Fig. 47. — Crystalline and other inclusions in the cells of various plants. 

 A, cystolith in subepidermal cell of Ficus leaf. B, crystal cells in Arctostaphylos. C, 

 druse in cell of Rheum palmatum. D-K, aleurone grains: D, E, from Myristica; F, from 

 Datura stramonium; G, from Ricinus communis; H, from Amygdalus communis; I, from 

 Bcrtholletia excelsa; J, from Fceniculum; K, from Elceis guiniensis. L, raphides in leaf 

 of Agave. M, inulin crystals in preserved cells of artichoke. (B-K after Tschirch.) 



possibly also chondriosomes, are concerned in this process. The peculiar 

 oil bodies found in the cells of certain liverworts appear to represent oil 

 vacuoles: these also have been discussed, together with elaioplasts, in 

 Chapter VI. Large masses of intranuclear metaplasm are found charac- 

 teristically in the eggs of gymnosperms. 



Aleurone grains occur in small vacuoles in the cells of many seeds, 

 particularly in such oily ones as those of Ricinus, Juglans, and Bertholl- 

 etia. In maize and wheat grains they are limited to a single layer of cells, 

 the " aleurone layer." The aleurone grain varies much in structure and 

 form, several types being described by Pfeffer in 1872. The grain con- 

 sists primarily of an amorphous protein substance, often with an outer, 

 somewhat more opaque shell. Some examples show no greater differen- 

 tiation than this, but many are much more elaborate (Fig. 47, D-K). 

 Those of Ricinus contain within them a single angular crystal of protein 

 (albumen), often referred to as the " crystalloid," and a globule of a double 

 phosphate of calcium and magnesium with certain organic substances 



