CHAPTER III 

 THE PLAXT-CELL 



WHILE a plant may consist of a single cell, much more commonly 

 it is made up of many more or less modified cells. The cellular 

 structure of plant-tissues was demonstrated by Robert Hooke, in 

 1667 ; but the real nature of the cells was first recognized a few 

 years later by the Italian Malpighi and the English botanist Grew. 

 Owing to the imperfections of the first microscopes, only the cell- 

 walls were seen by these investigators, and it was nearly two hun- 

 dred years later before the real structure of the cell was understood, 

 and it was recognized that the cell-wall is a secondary product of 

 the Protoplasm or living body of the cell. Protoplasm received its 

 name from the German botanist, Von Mohl, one of the brilliant 

 group of investigators who about the middle of the nineteenth cen- 

 tury laid the foundations of modem biology. It was soon made 

 clear that there was no appreciable difference between the proto- 

 plasm of plants and the so-called " sarcode " of animal tissues, and 

 the latter term was abandoned in favor of the former, which is now 

 universally employed to denote the living substance of both animal 

 and vegetable cells the "Physical Basis of Life," as it was so 

 aptly called by Huxley. 



Physical Properties of Protoplasm 



Protoplasm rarely occurs in quantity large enough to be readily 

 handled, being generally segregated in microscopically small masses 

 or protoplasts within the cell. There are, however, certain organ- 

 isms, notably the remarkable Slime-moulds or Mycetozoa (Myxomy- 

 cetes) which are composed of large masses of naked protoplasm. 

 These have long been the favorite objects upon which experiments 

 have been made. Such a mass of protoplasm has a slimy, viscid 

 consistence, much like the albumen of an egg, which it resembles 

 closely also in its chemical properties. The semifluid condition of 

 active protoplasm is due to its high percentage of water, which is 

 essential to the activity of all protoplasm. Much of this water 

 may be withdrawn without killing the protoplasm, but it then loses 

 the power of movement and enters a dormant condition. The dry 

 protoplasm has a horny consistence, but may be restored to the active 



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