jo6 LECTURE VIII, 



The vessels (wood-vessels) appear in relatively thick, vigorous bundles in various 

 forms, as annular vessels, as spiral vessels with one or more spiral bands, or as 



FIG. 141.— Transverse section of a primary root of a seedling of Phaseolus jnultiflorus ; taken from the upper swollen 

 portion, at the time wlien the first leaves and lateral roots are already developed, b bast and phloem ; 5 endodermis— vascular 

 bundle sheath ; pc pericambium mside the endodermis ; / primary and g secondary vessels ; in pith ; c cambium. 



Fig. 142. — Longitudinal section of the vascular bundle aiRicinus (cf. transverse section in Fig. 138). r cortical paren- 

 chyma ; gs vascular bundle sheath ; nt parenchyma of the pith ; b bast fibres ; / phloem parenchyma ; c cambium. The 

 cells between c and P eventually form a sieve-tube. In the xylem the elements are gradually developed from s to ff, 

 s primary, narrow, and very long spiral vessel ; 5' wide spiral vessel — both with unreliable spirals ; I scalarifomi — in part 

 reticular — vessel ; h and h' wood-cells ; t pitted vessel, with a resorbed septum at g ; h", h'" wood-cells > ff young pitted 

 vessel— the borders of the pits develope first, and then the pore arises inside At /, /, t', the boundary lines of the adjoining 

 cells — now removed — are observed on the walls of the vessels. 



reticulately thickened vessels, and finally as so-called dotted vessels or vessels provided 

 with bordered pits. In the development of a vascular bundle from the embryonal 



