136 



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 Phtiscolits vntltifloriis ; taken from the upper swoUe 

 portion, at the time when the first leaves and lateral roots are already developed, b bast and phloem ; s endoderniis— vascula 

 bundle sheath ; /c pericambium inside the endodermis ; f primary and ^ secondary vessels ; m pith ; c cambium. 



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

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

 cells between c and / eventually form a sieve-tube. In the xyleni the elements are gradually developed from j- to t'. 

 s primary, narrow, and very long spiral vessel ; s' wide spiral vessel— both with unreliable spirals ; / scalariform— in part 

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

 vessel— the borders of the pits develope first, and then the pore arises inside At /, t, 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 



