Lecture XX II. 185 



The stem grows in length at its tip. This tip is rounded and 

 is formed of small thin-walled cells, which fit closely together. 

 They are isodiametrical and polyhedral in form. Protoplasm 

 fills their cavities completely, and the nuclei of these cells are 

 comparatively large. At the extreme tip the cells divide at 

 short intervals and so their numbers increase rapidly. They 

 all resemble each other and are quite undifferentiated. At a 

 very short distance below the tip small excrescences on its 



FIG. 55. Pinus silvestris, growing tip of stem, longitudina section. 

 /, young leaves ; pc, procambial tracts. {From Evans' An Intermediate 

 Textbook of Botany.) 



side are developed. These are the beginnings of the scales 

 and of the dwarf shoots. At first the cells of these resemble 

 those of the extreme tip, being quite undifferentiated from one 

 another. Later on some of the deeper cells of the short shoots 

 and of the tip of the stem, which supports them, elongate and 

 divide longitudinally only, thus forming tracts running from the 

 scales and dwarf shoots into the apex, or tip, of the stem. These 

 are the procambial tracts and are the forerunners of the vascular 



