STRUCTURE OF TEE APICAL BUDS. 



123 



root-cap, but this is apt to be lost in removing the specimen 

 from the earth. 



The Embryonic Tissue or Meristem of the Rhizome. The 

 mature rhizome remains at the tip nearly undifferentiated into 

 tissues. At this point the epidermis may be distinguished, but 

 it remains very delicate, and the underlying cells continue to 

 grow and multiply, producing continued elongation of the mass. 

 In this way the apical bud is formed. Lateral buds are given 

 off right and left to constitute the embryos of leaves, branches, 

 or roots, which, always retaining their soft and delicate tips, are 

 capable of further growth. 



Behind these "growing points" the epidermis and other 

 tissues grow more and more slowly, and soon reach their maxi- 

 mum size, whereupon rapid growth ceases. The power of 

 growth is henceforward mainly confined to the apical buds, and 

 the growing tissue of which they are composed is known as em- 

 bryonic fissue ormeristem. 



The Apical Cell of the Rhizome. Close examination reveals 

 the fact that each apical bud contains a remarkable cell which is 

 especially concerned in the function of growth, viz., the apical 

 cell, which lies in a hollow at the apex of the bud. In the 

 apical buds of the rhizome or branches this cell has somewhat the 



a.c, 



FIG. 55A. (After Hofmeister.) Apical cell 

 of the rhizome in a vertical longitudinal 

 section, a.c, apical cell ; It, hair ; m, meri- 

 stem. 



FIG. 55 B. (After Hofmeister.) 

 Apical cell of the rhizome in hori- 

 zontal longitudinal section, a.c, 

 apical cell. 



form of a wedge with its base turned forwards and its thin edge 

 backwards, the latter placed at right angles to a plane passing 

 through the lateral ridges. It continually increases in size, but 

 as it grows repeatedly divides so as to cut off cells laterally 



