500 PHYSIOLOGY. 



the starch and the protoplasm are dissolved and stored away in the perma- 

 nent tissues. In plants kept in the dark Gris noticed that the chlorophyll- 

 grains slowly and gradually become smaller, lose their starch and their 

 colour, till at length nothing but a number of minute amorphous granules 

 remains. Some plants, such as Selaginella, some Ferns, &c., resist the 

 deprivation of light much more than others ; but in the case of quickly 

 growing plants, two or three days' obscurity suffice to disorganize the 

 chlorophyll. 



Action of Reagents on Nitrogenous Contents. The protoplasm, the nu- 

 cleus, and the chlorophyll-granules are all substances containing nitrogen 

 and closely allied to albumen ; they are more or less coagulable by heat, 

 alcohol, and acids, and soluble in caustic potash. The principal tests are 

 the following, though it must be remembered that their action is masked 

 by the colouring-matters of the cell, and that they are not in all cases 

 manifested in living, but only in dead cells : Iodine gives a brown or 

 yellowish tinge to these structures ; ammoniacal solution of carmine tinges 

 them pink. When treated with nitric acid, and subsequently with am- 

 monia, a yellow tint is formed, indicating the presence of xautho-protein ; 

 when soaked in a solution of copper sulphate and afterwards treated with 

 potash, a violet colour is produced in the protoplasm and chlorophyll ; 

 but this has not been observed in the case of the nucleus. It must be 

 remembered that the solubility of protoplasm in acids and alkalies depends 

 not only on the strength of the solvent, but also on the condition of the 

 substance at the time of the experiment. 



Aleurone exists in many seeds in the form of roundish co- 

 lourless granules pitted on the surface, or even presenting facets 

 like those of crystals. The granules occur between the starch- 

 grains, or, in the case of oily seeds, in large roundish or angular 

 masses. They are, for the most part, about equal in size; but here 

 and there one occurs much larger than the rest, and which is 

 remarkable for the rapidity with which it dissolves in water ; hence 

 it escapes observation under the microscope when the tissues are 

 examined, as they usually are, in water. Aleurone or protein-grains^ 

 as they are sometimes called, are insoluble in ether, alcohol, and oil ; 

 hence, in order to see the aleurone, the following process is 

 adopted : Thin slices of almonds or other seeds are soaked in 

 olive-oil, the oil is subsequently filtered and allowed to stand. 

 Some hours subsequently a white powder is precipitated ; this is 

 removed from the oil by nitration, and washed in ether or alcohol, 

 so as to remove the oil ; it is then allowed to dry, and the resulting 

 powder is pure aleurone. Aleurone -grains often contain, im- 

 bedded within their substance, crystals of calcium oxalate, or glo- 

 bose masses of magnesium phosphate. Aleurone is coloured brown 

 by iodine, and the inner portions of the grain assume a brick-red 

 colour after soaking for some minutes in a solution of mercuric 

 nitrate ; hence it is considered to be of albuminoid nature, and to 

 be of service in providing nutriment for the developing embryo. 



