CH. IV, 4] DEVELOPMENT OF STEMS 135 



anatomy are very stable in heredity, thus making them good 

 guides to the evolutionary history and present relationships 

 of plants. This important phase of investigation is now in 



FIG. 89. A single bundle in Corn (one from those shown in Fig. 74), 

 in cross section ; X 130. s points to the strand of phloem ; ra and sp are 

 ducts which, with the intermediate cells, form the xylem ; I is an air space 

 containing a ring, a, from a duct ; vg indicates the sheath around the bundle. 

 (From Strasburger.) 



active and successful development, but is somewhat too 

 special in method for further consideration in an introduc- 

 tory course. 



4. THE DEVELOPMENT OF STEMS AND LEAVES FROM BUDS 



Stems and leaves originate together in buds, though it is 

 more exact to say that the embryonic condition of a stem 

 with its leaves constitutes a bud. 



Most familiar of all are the winter buds of trees, in which 

 the bud proper is enwrapped within corky brown scales, 

 often with accessory linings of hairs or coatings of resin, as 



