CH. Ill] TISSUES. 37 



up of numerous cells, have a sort of individuality : each 

 cell grows, and behaves generally, as if it were coordinated 

 with all the other cells of the strand. The cells making up 

 the vascular strand behave like the soldiers of a regiment, 

 and give to the strand the same sort of unity that comes 

 from the combined and ordered behaviour of drilled men. 



On the other hand many tissues are chiefly character- 

 ised by being made up of a mass of similar cells. Thus 

 the tissue in which the vascular strands are imbedded 

 is a mass of simple rounded or angular cells, to which 

 the term parenchyma is applied, as in the case of the 

 similar tissue in the potato tuber; here the criterion of 

 unity of growth is not so obvious. 



Lastly some tissues are more especially tissues by birth- 

 right : that is to say they are classified together because 

 they are found to be developed in a similar way from an 

 embryonic cell or group of cells. Examples of tissues in 

 which this character is strong will be met with later on. 



I am now concerned to point out the difficulties which 

 meet the beginner in trying to seize the idea of a tissue. 

 On the whole it is best to let the conception grow 

 gradually : if he works out the histology of plants in the 

 laboratory, and reads books in which the terminology 

 is not incorrect, he will gain the idea in the best and 

 easiest manner. 



Root- cap. 



If a bean-root is held up against the light, it will 

 be seen that it ends in a conical point, 0, fig. 14, and that 

 inside the root a curved outline M can be dimly seen. The 



