110 



PHYSIOLOGY OF NUTRITION. 



longitudinal sections through the secondary wood of a twig of 

 Aristolochia Sipho about 1 cm. in thickness, we shall observe 

 numerous tracheides with bordered pits, together with narrow 

 and very wide vessels with bordered pits and annular diaphragms. 

 If we examine radial longitudinal sections of twigs of Berberis 

 vulgaris, we shall observe that the entire wood consists almost 

 exclusively of vessels with bordered pits, and of wood fibres. The 



FIG. 33. Longitudinal section of a vascular bundle of the fully elongated hypocotyl of, 

 Ricinus communis. r, cortical parenchyma ; gs, bundle sheath ; m, medullary parenchyma ; 

 b, bast fibres ; p, bast parenchyma ; c, cambium. In the wood the elements develop suc- 

 cessively from s to t' ; s, the first narrow very long spiral vessel, s', wide spiral vessel, the 

 spiral band in both cases partly unrolled ; I, vessel with scalariform and, in part, reticulate 

 thickening; h and 7i', wood cells ; t pitted vessel, with, at q, an absorbed transverse wall; 

 h' 1 and h'", wood cells; t', pitted vessel, still young. The pits first show the outer border, 

 the formation of the pore takes place later. We notice in the svall of the vessel in I, t, and 

 (', the outlines of neighbouring cells which have been removed. (After Sachs.) 



true spiral vessels of the primary wood of the vascular bundles 

 may be very beautifully seen, in addition to other elements (pitted 

 vessels, wood fibres, etc.), if we examine radial longitudinal sec- 

 tions of the stem of Helianthus annuus or of the fully elongated 

 hypocotyl of Ricinus communis. We employ alcohol material, 

 or in the case of Helianthus dried material will serve 4 (see 

 Fig. 33). 



It is instructive to separate the elements of the wood from one 

 another by the maceration method. We place a few crystals of 



