126 



CELLS AND TISSUES 



thoroughly modified for protection, absorption, strength, conduc- 

 tion, food-making, etc., in most cases growth and division ceases. 

 This brings us to the tissues which are groups of cells so modified 

 as to be adapted to special functions and upon which the various 

 activities of the plant depend. 



General View of Tissues 



The most important tissues of Seed Plants are those which have 

 to do with growth, protection, support, conduction, secretions, 

 absorption, food manufacture, food storage, and reproduction. 



FIG. 111. A, lengthwise section through a tip of a stem, showing the 

 apical meristem (ra) from which branches (6) are arising and from which cam- 

 bium (c) and other tissues are being formed below. B, cross section of a 

 stem, showing the cambium and its position in reference to other tissues. 



Tissues Connected with Growth. Since the cells of most tis- 

 sues are no longer capable of growth and division after completing 

 their modifications, there must be provided at certain places in 

 the plant groups or bands of cells which retain their ability to 

 grow and divide throughout the life of the plant, for otherwise 

 the growth of the plant would soon cease. Such cells, forming 

 the meristematic tissues or meristems (from the Greek word mean- 

 ing "to divide ")> are present at the stem and root tips and in the 

 cambium, where their chief function is the multiplication of cells, 



