Stem and Root Structures 



n 



A tissue is a group of cells which have had a common 

 origin, have developed in a similar manner so as to have the 

 same appearance, and have the same work to do : for example 

 we speak of the epidermal tissue, ground tissue, vascular tissue, 

 cortical tissue. At the apex of the stem the cells are alike 

 forming one tissue — primordial meristem. Close behind 



SI DP 



Fig. 73.— The growing point (highly magnified) of the stem of Pinus 

 sylvestris. D, dermatogen ; P, periblem and plerome ; SI, scale leaf (highly 

 magnified). (Photo-raicrograph by Flatters, Milbourne, & McKechnie.) 



the tip, this tissue shows a change : three tissues may be found 

 — {a) the dermatogen (Sep/ma, skin ; yewdo), I bring forth) or 

 protoderm (ttpojto?, first ; 8ep/xa, skin), (d) procambial strands, 

 (c) ground meristem. 



(a) The dermatogen divides by walls in two directions at 

 right angles to the surface walls, and, as the derivation of the 

 word indicates, forms the epidermis. 



(^) Farther down the stem, the procambial strands elongate 



