134 



MEDULLOSEAE 



[CH. 



spaces at regular intervals in the brown mesophyll. The axis 

 of the shoot consists of homogeneous parenchyma except near 

 the sloping sides where narrow dark bands (fig. 430, B, a) mark 

 the position of desmogen-strands of thin-walled elongated elements 



B 



FIG. 431. Dolerophyllum Goepperti. Transverse sections of leaves, e, epidermis ; 

 s, secretory cells ; t, transf usion-tracheids ; px, protoxylem. (British Museum.) 



representing an early stage in the development of vascular bundles 

 some of which have already produced spiral tracheids. Short 

 secretory cells accompany the immature conducting elements. 

 The lamina slightly exceeds 2 mm. in thickness in the broadest 

 part : the mesophyll is composed of large parenchymatous cells 



