PEANEROGAMIA. 



221 



468. The tissues of the Gymnosperms are individually 

 but little higher than those of the Fern-worts, but in their 



Fio. 185.— Diagrammatic cross-sections of stems, showing tlie fibro-vasoular 

 bundles, /c, of which x is the woody side and p the softer or bark side; 6, 6, 6, 

 bast-fibres; i2, M^ the fundamental tissues of the stem, of which B (the rind) is 



the cortical and M the medullary portion, or pith; ic. a belt of cambium which 

 extends from bundle to bundle. 



arrangement they show great and 

 important differences. The fibro- 

 vascular bundles are of the col- 

 lateral form, and are so placed in 

 the stem that the harder and more 

 woody side is nearer the centre of 

 the stem, while the softer side is 

 always nearer to the surface (Fig. 

 125, A). The inner part of the 

 bundles is composed mostly of long, 

 large cells, the tracheids, which 

 have the well-known characteristic 

 bordered pits (Fig. 126). The outer 

 part contains, besides other tissues, 

 a little fibrous tissue (bast-fibres). 

 Between these two halves of the 

 bundles there is a thin layer of 

 growing cells (cambium) which is 

 continuous with a layer between the bundles (Fig. 125, 

 A and J5). At this stage the stem is composed of an inner 



■Longitudinal sec- 

 tion of wood of a Pine (Pinus 

 sylvestris). Bordered pits, t',/', 

 t" ; a-e, parts of six tracheids ; 

 sl^ large pits, where medullary 

 rays touch tracheiids. Magni- 

 fied 325 times. 



