150 Autonomy of Cell-Organs 



dently do not lie in the chromatophores, and this, accord- 

 ing to Schmitz, is a general rule/^ But in the higher 

 plants this seems at times to be the case.* 



Last to be mentioned here are the microsomes. In 

 most cases it seems to be unknown what they are. Small 

 oil-droplets, starch-grains, inactive vacuoles, amyloplasts, 

 protein bodies formed by fixation*^ through the coagula- 

 tion of the protein dissolved in the protoplasm, and per- 

 haps many other formations are frequently all classed 

 under this name. Very justly has Strasburger claimed 

 "that not the microsome but the hyaloplasm is to be con- 

 sidered the active substance."*^ At any rate it ought 

 never to be forgotten that the word microsome stands 

 only for a question mark, and that we can talk of an in- 

 sight into the significance of these structures only after 

 the question concerning their nature in the cases con- 

 cerned shall have been answered. 



6. The Vacuoles 



Vacuoles were formerly regarded as empty spaces in 

 the interior of the protoplasm. This accounts for their 

 name, and explains the small interest shown in them, until 

 recently, in the study of the anatomy of the cell. It is 

 only since Sachs discovered that the turgidity of growing 

 cells is not due to an imbibition of water in their walls, 

 as was previously assumed, but to an osmotic tension be- 

 tween the wall and the cell sap, that attention was directed 

 to the significance of the vacuoles.'*^ 



^5 Schmitz. Loc. cit. p. 164. 



*^Cf. Meyer, Arthur. Das Chlorophyllkorn, pp. 14 and 31. 1883. 

 4*^ i. e. artifacts caused by the "fixing" fluid. Tr. 

 ^^Strasburger, E. Neue Untersuchungen. p. 107. 1884. 

 49Sachs, J. von. Lehrhuch der Botanik, 3 Aufl. 1872; 4. Aufl. 

 1874, p. 757. 



