THE STEM. 



35 



Very young stems of most gymnosperms, e.g., Scotch fir and 

 juniper, correspond A R 



in their main histo- 

 logical features with 

 those of dicotyledons 

 (fig. 7, A, B). The 

 most important dif- 

 ference is found in 

 the wood. This is 

 almost entirely made 

 up, not of vessels, 

 but of elongated 

 tapering elements, 

 with pitted lignified 

 walls and no proto- 

 plasm. These dead 

 skeletons of elon- 

 gated cells which 

 have lost their liv- 

 ing portion are 

 trache'ides. Wood 

 vessels and trache- 

 'ides may collectively 

 be called trachex. 

 The pits in the wall 

 are somewhat pecu- 

 liar. In surface 

 view they present 

 the appearance of 

 two concentric 

 circles, and are 

 therefore called bor- 

 dered pits (fig. 7, C). 

 The mouth of the 

 ™f • p if c nv.Pr.in o- Fia 7-— Minute Structureof Vegetative Organs [G, I, K, after 

 pit, t.t., 11& ujjttuuig Prantl]. All more or less magnified. A. cross-section of 

 young shoot of Scotch fir. B. part of same enlarged ; ep. 

 epidermis ; p. pith ; co. cortex ; x. xylem ; ph. phloem ; 

 c. cambium ; mr. medullary ray. C. small piece of radial 

 section of fir wood, showing trache'ides with bordered pits ; 

 mr. medullary ray. D. cross-section of asparagus stem, 

 showing bundles. E. one bundle of same, magnified ; x. 

 x'. xylem ; ph. phloem. F. piece of lower epidermis from 

 geranium leaf; g.c. guard-cells of stomata. G. cross- 

 section of beech leaf ; ep. upper epidermis ; ep'. lower 

 epidermis ; pp. palisade parenchyma ; *p. spongy paren- 

 chyma ; st. stomata. H. part of cross-section of buttercup 

 root; ep. epidermis; Ir. lateral root; gt. cortex; rh. 

 root-hairs. I. section of elder lenticel ; ep. epidermis ; 

 co. cork; I. loose cork of lenticel; c.c. cork cambium. 

 K. part of cross-section of four-year-old lime twig ; p. 

 pith ; co. cortex ; c. cork ; ph. phloem ; x, i , 2 , 3,4. 

 annual rings of xylem. 



into the cavity of 

 the tracheide, is 

 narrower than the 

 bottom of the pit, 

 and (the whole sec- 

 tion being transpa- 

 rent) it therefore 

 appears as the inner 

 circle, and the latter 

 as the outer. In gym- 

 nosperms, again, the 



