CRYSTALS. 59 



Thin sections of the seeds of the Castor Bean (Ricinua communis), 

 after the removal of other substances by soaking in water for some 

 time, show tetrahedral or octohedral crystalloids. 



(6) Aleurone and the crystalloids furnish the greater part of the al- 

 buminoid portions of edible grains. The amount of albuminoids is 

 presumably an indication of the amount of aleurone and crystalloids. 

 The percentage of albuminoids in some air-dry grains and seeds is given 

 below : * 



Rice 7.5 



Barley 9.5 



Indian Corn 10. 



Oats 12. 



Wheat 13. 



Pea 22.4 



Bean 25.5 



Vetch 27.5 



Lupine 34.5 



Aleurone and the crystalloids appear to be resting states of proto- 

 plasm analogous to the resting states (sclerotia) of the plasmodia of 

 Myxomycetes. 



IV. CRYSTALS. 



78. In many plants crystals of various forms occur either 

 in the cavities of cells, or in the substance of the cell-walls, 

 or even in intercellular spaces. They are, in the greater 

 number of cases, composed of calcium oxalate, and are widely 

 distributed throughout the vegetable kingdom, but appear 

 to be most numerous in the higher groups, and least so in 

 Bryophytes and Pteridophytes. 



79. It is common to distinguish the acicular (needle- 

 shaped) crystals from the other forms under the name of 

 Raphides ; these have but two equivalents of water of crys- 

 tallization in their composition ([Ca 0] 2 C 4 B + 2 H 2 0). 

 They are found in the cavities of parenchyma-cells, and lie 

 parallel together in bundles of ten to fifty or more. Upon 

 slight pressure the crystals separate and escape (Fig. 46). ( 



The other crystals of calcium oxalate assume various 

 forms, such as prisms, octahedra, etc. They have six equiv- 



* These percentages are from Wolff and Knop's tables, as given by 

 Professor S. W. Johnson in his valuable " How Crops Grow." 



