Stem Structure 



4r 



At first this is like the epidermis of the root, consisting of 

 a number of similar cells, always completely in contact ; but 

 after a while some of these become separated from one another, 

 leaving an opening or stoma (plural, stomata) between them 

 (fig. 64). 



These stomata are always surrounded by two or four cells, 

 which are generally smaller than the epidermal cells, are cres- 

 cent-shaped, and contain chlorophyll. These are known as 

 stomatal or guard cells. i_ 



Fig- 63. — Transverse section of petiole rA Hel~ 

 lebonis, showing the three systems of tissues : 

 e. epidermal ; _/J fibro-vascular : x, xylem ; 

 c, b, phloem— c, soft bast ; ^, bast-ftbres ; g, 

 ground or fundamental tissue. (After 

 Prantl.) 



Fig. 64. — I. Horizontal section through 

 the epidermis of the under side of 

 the leaf of Euonymus japonicns 

 looked at from below : jr/, stoma' a 

 II. Course of development of the 

 stoma of yj rthropodiiim cirrhatitm : 

 spin, mother cell ready for division : 

 sp\ sp", sp'", successive stages of 

 division. III. Mature stoma. 



More towards the interior of the stem there are developed 

 some bundles of cells (fig. 63). At first these bundles consist 

 of meristem tissue, known as prooambium, forming a string of 

 similar and growing cells. Very soon, however, the greater 

 part of this passes into the form of permanent tissue, which 

 is separated into an outer or phloem and an inner or xylem 



