158 The Living Plant 



plant, where it has been sought; and it seems clear that every 

 living cell is thus in communication with its neighbors, and 

 therefore with every other living cell of the plant. Thus the 

 protoplasm though partially, is not wholly, separated into cellu- 

 ^ , f;. lar masses, and is, after all, for any 



, . / individual plant a single great con- 



. ,: ;:; ; ;^ ^^i/ ,#' tinuous sheet. There is every reason 



/ . :\ v? ^fif? to believe that impulses of different 



''""; "" ";:"' v/'^fW' 1 , kinds can be transmitted from cell 

 ';':'' </nZ to cell through these threads, which, 



therefore, take the place in part of 

 the nerve system of animals. This 

 - helps us to understand how it is that 

 : '\r$ I ; -^ . : ,t, ; >< the plant can act as a physiological 



'^~^ : :' f'-^^^-^^^^lr^ unit: how the different parts of a 

 plant can be kept in harmonious 

 FIG. 5i. An ordinary ceil specially cooperation : and how stimuli applied 



treated to show the thin threads 



of protoplasm extending through at one part of a plant, can produce 

 !Jith^hat^flts l n3ghre. r0 (CoS their effects at a considerable dis- 



from Strasburger's Lehrbuch). 



Thus much for the wall of the cell, to which, it may seem to the 

 reader, I have devoted a disproportionate space and attention. 

 Yet while vastly less important than the protoplasm, the solidity, 

 prominence, and relative permanence of the walls makes them far 

 more accessible to study, to such a degree indeed that our con- 

 ceptions of cellular structure center much more largely around 

 the walls than the protoplasm.* This, however, is less unfortu- 



* The inconspicuousness of the living protoplasm of plants in comparison with 

 the prominence of the walls it builds finds striking exemplification in the history of 

 their discovery ; for the mass of the walls was well described, and their cavities were 

 named cells, by Robert Hooke as early as 1667, while they were elaborately described 

 and beautifully pictured only a few years later, 1672-1682, in the fine books of Grew 

 and Malpighi. But the protoplasm was not recognized at all as a constituent of 

 cells until over a century and a half later, and was only first adequately described 

 and named by von Mohl, in 1844. 



Here is Hooke's sentence, of 1667, in which cells were first named. He is describ- 



