MORPHOLOGY OF HIGHER PLANTS. 173 



then numerous oil globules appear in the protoplasm around it; 

 later some of the walls of the cell thicken and grow around the 

 crystal, which they finally completely envelop, as in Moracese. 



COMPOSITE BODIES. 



Aleurone or protein grains are made up of protein-crystal- 

 loids, globoids and a ground mass, the whole being enclosed by a 

 membrane-like material (Fig. 122, D). Calcium oxalate crystals 

 may, or may not, be present; when they do occur, they are of 

 special value in the study of the plants in which they are found, 

 as in the fruits of the Umbelliferae. 



The aleurone grains arise in the cell-sap, usually in that of 

 seeds ; the calcium oxalate, if present, separates first ; then the 

 globoids, which are small globular bodies composed of the double 

 phosphate of calcium and magnesium, appear ; after which the 

 crystalloids arise ; and finally, from the mother liquor, the ground 

 mass separates, the whole becoming enclosed in a membrane. 



Aleurone grains may be studied by taking advantage of the 

 difference in solubility of the substances composing them. The 

 membrane is a protoplasmic membrane and, while soluble in water, 

 remains intact on examining sections in any of the fixed oils, as 

 cotton-seed oil. Usually seeds which contain aleurone are rich in 

 fixed oils, and if this oil is first removed by placing fresh sections 

 in alcohol, or alcohol and ether, the subsequent study is facilitated. 

 If the sections thus treated are mounted in water, the membrane 

 gradually dissolves, leaving the crystalloids, globoids and calcium 

 oxalate. On adding a o.i to r per cent, solution of either sodium 

 or potassium hydrate, the crystalloids dissolve, the globoids and 

 calcium oxalate crystals remaining unafifected. The globoids may 

 be dissolved by the use of a i per cent, acetic acid solution, or 

 concentrated solutions of ammonium sulphate or monopotassium 

 phosphate. The calcium oxalate remaining may then be treated 

 with hydrochloric acid in the usual way. 



II. AMORPHOUS SUBSTANCES. 



Cystoliths. — Occasionally cells are found among the paren- 

 chyma or in the inner row of the epidermal cells on the upper side 



