260 STRUCTURAL BOTANY 



up by tangential walls, and thus give rise to a 

 phellogen which forms cork-cells on its outer side 

 (see Figs. 104, 105, 106, pd). From this time 

 onwards the root ceases to be an absorptive organ. 

 The corky periderm completely isolates the cortex 

 from all communication with the conducting cylinder, 

 and consequently the whole external tissue, from the 

 endodermis outwards, dies away. Henceforward the 

 root is an organ of conduction only, consisting solely 

 of the central cylinder, which by means of its cambium 

 retains the power of unlimited growth. In all these 

 respects the root of a Conifer agrees closely with that 

 of a typical Dicotyledon. 



d. Growing Points and Lateral Appendages 

 a. Growing -Point of the Stem 



The apex of the shoot in a Fir has essentially the 

 same structure as that of an angiospermous plant. 

 It consists of meristem, the cells of which are small, 

 and have the usual characteristics of embryonic tissue, 

 large nuclei, abundant protoplasm, and thin cell-walls 

 (see Fig. 107). 



The formative layers of the meristem are less 

 distinct here than in Angiosperms. Whereas in the 

 latter it is a constant rule that the external layer of 

 the apical meristem gives rise to the epidermis only, 

 this is not the case in Conifers. Here the superficial 

 cells of the growing - point may divide by walls 

 parallel to the surface, and thus contribute to the 

 formation of cortical as well as of epidermal tissue 



