GLOSSARY. 249 



tion of the development of all living things from cells. 

 A cell-wall, cell-contents, and a nucleus, were formerly 

 regarded as essential, but further investigation has shown 

 that a cell is essentially a semisolid mass of living matter. 



Chlorophyll. The green coloring matter of vegetables. 



Chromatic Aberration. The errors depending on the 

 unequal refrangibility of the colored rays which make up 

 white light. 



Ciliary Motion. The movement of cilia, or minute hair- 

 like bodies, on animal and vegetable cells. The cause of 

 it is unknown. 



Colloid. Substance devoid of crystalline power, as 

 gum, albumen, gelatin, etc. Such substances pass slowly 

 through a membrane, while crystalloid bodies pass readily, 

 thus enabling us to separate them by dialysis. 



Correlation of Forces. The doctrine that any one of 

 the forms of physical force may be converted into one or 

 more of the other forms. 



Cryptogamia. Lower orders of plants, whose fructi- 

 fication does not depend on the presence of stamens and 

 pistils in the flower. 



Crystallography. The science which treats of the laws 

 by which the surfaces of crystals are disposed to one 

 another. 



Crystalloid. Substances capable of crystallization. 



Cydosis. A circulation of fluid in the cells of plants. 



Definition. The power of an object-glass to give a dis- 

 tinct image of an object. 



Diaphragm. A stop for intercepting some of the lu- 

 minous rays, generally placed just beneath the micro- 

 scope stage. 



Diffraction of Light. A disturbance of the straight 

 path of a ray of light from its passage close to the edge 

 of an opaque body. 



Double Refraction. The power possessed by some crys- 

 tals, as Iceland spar, of exhibiting two images. The po- 



