166 



PHYSIOLOGY OF NUTRITION. 



examined under the microscope, it is seen that, under the strongly 

 cuticularised epidermis, green tissue and groups of sclerenchy- 

 matous fibres alternate with each other. Under the bundles of 

 sclerenchyma fibres are to be seen large cavities filled with air; 

 and we further perceive embedded in the ground tissue many 

 vascular bundles, the wood and bast of which are readily distin- 

 guishable. Each vascular bundle is provided both inside and 

 outside with a layer of sclerenchyma fibres. If we split a haulm 

 of Juncus glaucus longitudinally, it is seen that the wide cavity 

 in the middle is not continuous, but is chambered. The cavity of 

 the haulm is traversed by numerous plates of tissue, the so-called 



diaphragms, which are seen 

 under the microscope to 

 consist of many-rayed star- 

 shaped cells. 



If we prepare a trans- 

 verse section through an 

 internode of a vegetative 

 shoot of Equisetum arvense, 

 the characteristic arrange- 

 ment of the green paren- 

 chyma on the one hand, 

 and of the hypodermal 

 strand of sclerenchymatous 

 fibres under the epidermis 

 on the other, is readily 

 made out even under low 

 magnification (see Fig. 57). 

 Then follows large-celled 

 cortical tissue enclosing wide air cavities, the so-called vallecular 

 canals. The circle of vascular bundles is surrounded by an endo- 

 dermis, and each bundle is clearly differentiated into wood and 

 bast. In the wood a wide intercellular passage, the carinal canal, 

 is easily seen. Finally, the hollow pith and the comparatively 

 narrow intercellular spaces between the cells of the cortex and 

 pith are to be noted. 



On microscopic examination of a delicate transverse section 

 from the leaf-stalk of Nymphasa alba we perceive an epidermis 

 free from stomata, and below this a ring of collenchyma. In 

 the peripheral region of the leaf-stalk occur the vascular bundles, 

 arranged in a circle ; but there are also fibro-vascular bundles 



FIG. '67. Transverse section through the 

 internode of a sterile shoot of Equisetum 

 arvense. m, the pith; cl, carinal canal in the 

 vascular bundle ; e, endodermis ; vl, vallecular 

 canal; Tip, strand of sclerenchyma fibres; ch, 

 green tissue; st, stomatal apparatus. (After 

 Strasburger.) 



