58 BOTANY. 



75. — Aleurone grains appear in seeds during the last 

 stages of ripening. In the turbid cell-contents, as the loss 

 of water proceeds small globular masses of albuminous mat- 

 ter appear, and afterward increase their size ; by the con- 

 tinued loss of water they become harder and of a more defi- 

 nite outline. In the germination of the seed the aleurone 

 grains dissolve, and the protoplasmic contents of the cells 

 assume very nearly the condition they held before the final 

 changes in the seed which produced the aleurone. 



Aleurone may be studied in the seeds of the bean, pea, vetch, and 

 lupine, and in acorns, chestnuts, horsechestnuta, and the bran-cells of 

 the oat-grain. 



The development of aleurone grains may be best studied in the 

 ripening seeds of the peony. 



76. — As with the grains of aleurone, the nature of crystal- 

 loids is not fully understood. They are quite certainly modifi- 

 cations of protoplasm, and not true crystals, although they 

 are bounded by plane surfaces, have sharp edges and angles, 

 and when viewed by polarized light bear a resemblance 

 to crystals. Their deportment with reagents, however, 

 is similar to that of protoplasm ; thus, under treatment 

 with iodine, or nitric acid and potash, and in their coagula- 

 bility, they show a protoplasmic nature. They possess the 

 power of imbibing water, but are not dissolved in it, and in 

 a dilute solution of potash they swell greatly, at the same 

 time altering their angles. They are insoluble in alcohol. 

 In dilute acids or glycerine one portion of their substance is 

 removed, leaving a skeleton. 



77. — In form they are cubical, tetrahedral, octahedral, 

 rhombohedral, and of other shapes, and there is generally 

 such irregularity in their forms that it is difficult to deter- 

 mine to which crystal system they belong. In most cases 

 they are colorless, but in some plants they contain a coloring- 

 matter which may be removed by alcohol and acids. 



(a) Common examples for study may be obtained from the parenchy- 

 ma-cells beneath the skin of the potato tuber, in which they are cubi- 

 cal or tetrahedral, and imbedded in the protoplasm. 



They may be obtained from the Brazil-nut [BerthoUetia excelsa} by 

 placing portions of the crushed seed in a test-tube and agitating it with 

 ether ; the crystalloids, which settle to the bottom, are tabular. 



