24 COMPENDIUM OF GENERAL BOTANY. 



(albuminoid substance). Generally these crystals originate within 

 the cytoplasm. As proof of such origin we have in addition to the 

 albuminoid nucleus of the clusters the presence of an albuminoid 

 covering to such crystals. Sometimes a wall of cellulose is formed 

 around them. It must, however, be noted that sometimes no 

 plasmic covering can be demonstrated. 



Silicious bodies ("Kieselkorper") have also been observed within 

 the cell. 



As will be seen later, these same substances which have been 

 mentioned as occurring in the cell may also impregnate the cell- 

 wall. We shall here add a few remarks on plant-mucilage, though 

 it does not belong to the solid plasmic inclusions. Raphide (see 

 cells foregoing) usually contain a mucilaginous substance. It forms 

 the officinal Salep mucilage of Orchid tubers. It seems probable 

 (FRANK) that this substance originates within the plasm as a spherical 

 body finally enclosing the raphides and filling the entire cell-lumen. 

 STAHL, whose investigations concerning " plants and snails " we have 

 already mentioned, ascribes to this mucilage enveloping the raphides 

 the function of an " expulsor" of the acicular crystals. As soon as 

 some animal wounds the cell, the mucilage which is under pressure 

 partially forces out the sharp needlelike crystals. The raphides 

 are more numerous toward the outer surface of the tubers ; the 

 mucilage is more abundant toward the interior. This mucilage also 

 serves as reserve material, since it is dissolved when the tubers begin 

 to sprout. Plant-cells may also contain sph aero-crystals of calcium 

 oxalate besides the above-mentioned perfect forms. 



C. THE CELL- SAP AND THE REMAINING FLUID CONTENTS OF THE 



CELL. 



The fluid filling the vacuoles, or more often in mature cells 

 almost the entire cell-lumen, is called cell-sap. It contains various 

 substances in solution : glucose, cane-sugar, inulin, asparagin, organic 

 acids, inorganic salts, coloring materials, and occasionally still other 

 substances. When plant-tissue is placed in alcohol, inulin is 

 deposited in the form of sph aero-crystals (PRANTL). Very often cell- 

 sap contains red and blue coloring material in solution. (Notwith- 

 standing this colored cell-sap, plasm is almost without exception 

 colorless, leaving out of consideration the cliromatophores.) 



Oil-droplets (chemically not easy to define) and equally refractive 



