184 PART II. THE INTIMATE STRUCTURE OF PLANTS. [ 34. 



be traced quite to the extremity ; they disappear further back, 

 and their place is taken by parenchymatous cells. 



Bundles often terminate in connection with glandular tissue ; 

 for instance, in chalk-glands (see Fig. 100, p. 139), or nectaries. 



34. Histology of the Development of Secondary 

 (Vjembers. It has been already pointed out (p. 17) that the 

 growing- point is the seat of development, not only of new tissue, 

 but also of new members ; and further (p. 19), that secondary 

 members are developed either by dichotomy or by lateral out- 

 growth . 



A. Development of normal branches of the shoot or of the thallus. 

 only takes place at the growing-point, whether apical or inter- 

 calary. 



a. By dichotomy. This only occurs in apical growing-points ; 

 two modes may be distinguished accordingly as the growing-point 

 has or has not an apical cell : 



4 



FIG. 140. A B C successive stages in true dichotomous branching by longitudinal 

 division of an apical cell ; from the shoot of Dictyota dichotoma (highly magnified ; after 

 Naegeli). 



wlien there is an apical cell, true dichotomous branching is 

 effected by the longitudinal division of the apical cell into two, 

 each of which becomes the apical cell of a branch : 



A spurious form of dichotomy occurs in some plants (e.g. thalloid Junger- 

 mannieae) ; here, though the apical cell of the branch is developed from a seg- 

 ment of the apical cell of the main shoot, yet since the really lateral branch 

 grows quite as vigorously as the main shoot, the result is an apparently dicho- 

 tomous branching. 



when there is no apical cell, the growing-point becomes 

 broadened, and the central portion of it passes over into condition 

 of permanent tissue, leaving two distinct masses of embryonic 

 tissue, which constitute the growing-points of the two branches 

 (e.g. March an tiaceee). 



b. By lateral outgrowth ; this may occur in either an apical or 

 intercalary growing-point : 



