1 82 SCIENCE FROM AN EASY CHAIR 



This has now been found by improved methods of micro- 

 scopic examination to be a mistake. The cell-wall in a 

 great many plants, though so firm and cleanly cut in 

 appearance, is yet perforated by fine threads of the cell 

 protoplasm, so that each cell is in living communication 

 with its neighbour. Thus, in plants as well as in animals, 

 the individual cell-units form a more or less continuous 

 whole of living matter, separated by dead, inert cell- 

 walls and products of cell activity ; but, nevertheless, con- 

 nected in definite tracts and regions to one another by 

 continuity of the living matter in the form of excessively 

 fine threads. 



Those animals and plants which are built up of many 

 cells of many varieties that is to say, all but the micro- 

 scopic unicellular kinds may be considered as compo- 

 site organisms cell-states or communities in which the 

 individual cells, all derived from one original mother-cell, 

 are the citizens, living in groups and habitations (tissues), 

 having their different occupations and capacities, carrying 

 on distinct operations and working together for the 

 common good, the " life," as we call it, of the individual 

 plant or animal which they constitute. This comparison 

 should serve merely as an illustration of the individual 

 character and co-ordinated activity of the cells of a many- 

 celled plant or animal. It must not be forgotten that the 

 separate cells are all derived by binary division from the 

 original germ-cell, that they have not come into juxta- 

 position from distinct sources, but often are held together 

 by threads of their living material, which remain after the 

 process of division of one cell into two. 



Protoplasm has been called " the physical basis of 

 life." Since the activities to which we give the name 

 " life " reside in protoplasm, and are chemical and 

 physical activities like those of other bodies, even though 

 more subtle and complicated we are justified in regard- 



