10 



OF WOOD IN GENERAL. 



thickened, and turn from white to brown; but even then its 

 relatively minute width makes it difficult to detect in a stem 

 several years of age. 



FIG. 4. Transverse section of the stem of Traveller's Joy (Clematis Vitdlba), 

 showing relatively large central pith and large vessels. 



The procambium strands extend from the rudiments of leaves near 

 its apex right through the stem into the root. They get their 

 name from a Latin word, cambio, to grow, being in a merely 

 transitory or embryonic condition. In Monocotyledons the whole 

 of their tissue passes into the condition of wood and bast ; so that 

 the bundle, as the strand in its permanent form is termed, being 

 incapable of any further growth in diameter, is said to be dosed. 

 It is because it gives rise to a bundle (Greek, desmos, a bond) that 

 the procambium is termed desmogen. In those trees, however, with 

 which we are concerned, viz. Gymnosperms and Dicotyledons, 

 whilst the inner portion of each strand becomes wood or xylern 

 (Greek, xylon, wood) and the outer part bast or phloem (Greek, 

 phloios, bark), a band between these two parts remains embryonic. 

 This layer is called the cambium, or more precisely, for a reason 



