86 



PLANT LIFE. 



tinguisbed from the root by not forming through segmenta- 

 tion from the outer faces of the initial cell or cells a many- 

 layered epidermal cap. In further contrast with the root, 

 which often has no true epidermis except the root-cap, the 

 shoot is characterized by possessing an uninterrupted epider- 

 mis over its entire surface, consisting always at first of a 

 single layer of cells. This epidermis persists as a surface 

 covering either throughout the life of the shoot, or for a long 

 period, being replaced only upon the 

 older surfaces of the axis by subsequently 

 formed protective layers. (See ^[ 134.) 

 103. Branching. — Branches of the 

 <^X JJ^Zg shoot arise from lateral buds, which are in 

 all respects similar to the terminal buds 

 just described. If, for any reason, the 

 terminal bud of the stem becomes de- 

 stroyed, or its growth arrested, a branch, 

 developing from a lateral bud near by, 

 may assume the position and habit of 

 the main axis, its own normal mode of 

 development being altered. In many 

 plants the death or arrest of the ter- 

 minal bud recurs at regular intervals. 

 In such plants, therefore, the main axis 

 is really a succession of lateral branches, 

 and the branching is said to be sympo- 

 dial (fig. 97). In some plants, e.g., 

 lilac, two lateral buds standing at the 

 same level may develop, if the terminal 

 one fails. In this case the shoot seems 

 to divide into two equal branches. This, 

 however, is not true, but false, or sym- 

 podial, dichotomy. True dichotomy, like true dichotomy of 

 the root, occurs only in those plants in which the axis has 



Fig 97. — Shoot of Euro- 

 pean linden, t, the last 

 internode formed by the 

 bud of present season. 

 This dies and drops off 

 and the shoot will be 

 formed next year by the 

 last axillary bud, a, 

 which appears to be 

 terminal after loss of /. 

 Half natural size. — After 

 Frank. 



