VASCULAR BUNDLE OF IRIS. 



115 



iively narrow cells, with abundant cell-contents, of the primary 



wood parenchyma. Similar cells also surround the vessels on 



the flanks of the bundle, and separate them from the ground- 



tissue (shaded cells 



in Fig. 42). At the 



inner margin of the 



wood are always 



to be seen some 



crushed elements, 



the protoxylem (ss), 



whose walls are 



stained like those 



of the vessels. The 



bast again shows 



an alternation of 



larger and smaller 



cells ; the contrast 



is here, however, 



not so striking, nor 



is the regularity of 



arrangement so 



great, as in Zea. 



The cells with 



broader cavities are 



the sieve - tubes, 



the smaller ones, 



marked by their 



abundant cell-con- 



tents, the com- 



panion - cells. In 



the outer region of 



FIG. 42. Cross-section of a vascular bundle from the leaf 



the bast lie the O f Iris fl&rentina. With dark contour are the vessels ; the 



r-.vr.fr. ce H s f th e bundle which are rich in contents are shaded, ss, 



p 1 O I O- crushed protoxylem ; sp, broader spiral vessels or tracheides ; 



elements sc, scalariform vessels or tracheides ; v, sieve-tubes, between 



, . , which are the narrow companion-cells ; pr, crushed proto- 



(pr), to Which we phloem elements ; vg, sheath with wavy radial walls ; k, 



have already re- section throu g h a cr J' stal ( x 24 )- 

 f erred, which have ceased to function, and which have swollen 

 walls more or less deeply stained blue. This outer bast portion 

 is enclosed by the strongly thickened sclerenchyma of the sheath, 

 which supports the vascular bundle with a more or less strongly 

 developed strand. Around the remainder of the vascular bundle 



phloem 



