54 THE INTERNAL 



insoluble. Regarding the former, we can arrive at no 

 conclusions by the microscope, since they disappear in the 

 watery cell-sap ; chemistry alone can then demonstrate their 

 presence. To this class belong, among others, albumen, 

 gum, sugar and the agreeable acids of our fruits, such 

 as the malic and citric acids. The sap of the Sugar-cane 

 is perfectly clear and transparent in the cells, the dissolved 

 sugar only appears after the expression and evaporation of 

 the fluid. 



The fluid oils, on the contrary, are very readily dis- 

 tinguished beneath the microscope, both the fat oils, which 

 swim in the cell-sap in the form of little shining yellow 

 globules, as in the kernel of the almond, and the aromatic 

 (etherial) oils which usually occur alone and fill a whole cell 

 in one large drop. 



Two of the most important constituents in the vegetable 

 cell, however, are the semi-fluid, half-granular mucus, 

 composed of a nitrogenous substance, which either wholly 

 fills the cells or occurs with oil or starch, and this latter 

 substance itself. Certain nitrogenous constituents form 

 the peculiar nutrient matter in plants. One portion, 

 albumen, occurs dissolved in the cell-sap ; another and 

 more important, in small mucous granules. If we make 

 a cross-section of a grain of wheat or rye, and place it 

 under the microscope, we perceive very distinct layers in 

 it as we examine from without inwards. The outer of 

 them belong to the husk of the fruit and seed, (PI. n, 

 Fig. 2, ,) and are separated as bran in grinding. But the 

 mill-stone does not separate so exactly as the eye may 

 by means of the microscope, not even so accurately as 

 the knife of the vegetable anatomist, and thus with the 

 bran is separated also the whole outer layer of the cells 

 of the nucleus, and even some of the subjacent layers. A 



