No. 449.] STUDIES ON THE PLANT CELL. 389 



condition are the cells filled with cytoplasm so homogeneous in 

 structure that only the most delicate granules (microsomata) can 

 be distinguished in the clear substance. 



Waste products such as mineral matter, resins, certain oils, 

 solutions of tannin and various poisons, such as the alkaloidfs, 

 may be easily recognized. Most food substances such as starch, 

 proteid grains (aleurone), albumin crystals, oils, fats, etc., are 

 readily separated from the protoplasm in which they lie. But 

 the difficulties are much greater with the smaller particles of 

 proteid material, which are frequently such minute granules as 

 to approach the microsomata in size. These may give to the 

 protoplasm a granular consistency that breaks up the foam or 

 spongiose structure characteristic of the pure condition. These 

 granules are undoubtedly in most cases substances intimately 

 concerned with the metabolism of the cell and are members of 

 the chains of constructive and destructive processes that charac- 

 terize life phenomena. 



The other non protoplasmic structures of cells are vacuoles 

 which are essentially bubbles of fluid lying in the denser proto- 

 plasmic medium and surrounded by plasma membranes. The 

 watery fluid of vacuoles contains various substances in solution, 

 carbohydrates such as the sugars glucoses and inulin, mineral 

 salts, asparagin, tannin, alkaloids, etc., and occasionally oil and 

 not infrequently crystals. Vacuoles may be formed in large 

 numbers in protoplasm. They tend to run together as do 

 bubbles in a froth and in this way the large central vacuole 

 becomes established in the cell, gathering to itself many smaller 

 vacuoles until the protoplasm is forced to lie as a relatively thin 

 layer next the cell wall. The fluid in the central vacuole (cell 

 sap) is generally thinner and more watery than that in the 

 smaller vacuoles. The latter are apt to be more rich in albumen 

 which may be transformed into proteid grains as is especially 

 well illustrated in the secretion of aleurone. Cell sap may be 

 colored by pigments in solution and the tints of flowers are 

 largely due to this cause alone or to the effects of its color in 

 combination with various plastids in the cell. 



It is possible that physodes, described among the cytoplasmic 

 structures, are in reality vacuoles filled with substances other 

 than cell sap, which are not as yet understood. 



