116 



A TEXTBOOK OF BOTANY 



[Ch. IV, 2 



bud developing the leaves, which are there small and close, 

 but which downward are progressively larger and more 

 widely spaced apart (Fig. 69). The leaves stand usually 

 upon slight annular swellings of the stem, sometimes ob- 

 scure and sometimes well marked, called nodes, which are 

 separated by smooth cylindrical leafless internodes. In 

 the axil of each leaf occurs a small bud, the foundation of a 



branch, which later de- 

 velops and bears leaves 

 precisely in the manner of 

 the main stem. 



In their tissues, herba- 

 ceous stems are much like 

 the leaves, as to chloren- 

 chyma, epidermis, stomata, 

 trichomes, and peculiari- 

 ties of color. The veins, 

 however, do not show to 

 the eye, being buried within 

 the cylindrical stem. In 

 cross sections cut close to 

 the bud one sees little more 

 than the general growth 

 tissue, but farther back ap- 

 pears some such aspect as 

 that of our picture (Fig. 

 70). Beneath the thin 

 epidermis lies the chlorenchyma, pale green but rather thick, 

 obviously aiding the leaves in food formation. Centerward 

 can be seen the cut ends of the veins, called also vascular, 

 or fibro-vascular, bundles, which run lengthwise of the 

 stem, and have the same general structure, and the same 

 function of conduction for water and food, as in the leaves. 

 Commonly they are arranged in a ring, in which case they 

 enclose a pith, of loose open texture, often glistening-white 

 from included air. The pith is especially the storage part of 



Fig. 70. — The tissues of a typical 

 herbaceous stem, of the Stock, in cross 

 section ; X 55. The cambium is repre- 

 sented by the heavier double line through 

 the fibro-vascular bundles, which are 

 seven in number. The collenchyma is not 

 marked. (From Scott, Structural Botany.) 



