148 



PLANT LIFE. 



in acti\'e motion (fig. i68), or when tlicy extend a portion of 

 the body as a pseudopodium (fig. 169). 



Fig 169, — Plasmodia, creeping bits of naked protoplasm, showing \'aiied shapes as 

 parts are protruded or withdrawn. Highly magnified. — After Kerner. 



188. Turgor. — If the organi.sm be one surr(jiinded by a 

 cell-wall, or if it be made up of a number of cells united, the 

 cell-wall itself plays a considerable part in maintaining the 

 form. This is due to the condition of the cell known as 

 tiu'gor. AA'hen fnlh' mature the cell-wall of each active 

 cell is lined by a more or less thick layer of living j^roto- 

 plasni. In the interior of the protoplasm there exist one or 

 more water chambers, the vacuoles (^| 5). If such a cell as 

 this be measured in its normal condition, and tlien surrounded 

 for a few moments bv a 10 per cent, solution of common salt, 

 re-e\aniination will sliow that the vacuoles have been dimin- 

 ished, the protoplasm shrunken away from the wall, and 

 remeasurement will show that the cell has diminished both in 

 length and diameter. In its normal condition, therefore, the 

 wall was stretched b}' the pressure of the contents within. If 

 a cell which has been thus shnmken by immersion in a solu- 

 tion of salt be again placed in water, it may regain, in the 

 course of a few hours, its original condition, that is, it may 

 again become turgid. This -would be fjrought about by the 

 entrance of "\\'ater into the vacuoles to replace that withdrawn 

 wlien the cell was placed in the solution of salt. 



If a thin piece of ruljber tubing be connected with a pump 

 and filled with «ater until it is stretched, it increases its 



