OF LOWER GREENS AND PLANTS. 285 



actual sections. One end of the block is weathered out, and tho 

 wood-texture with the broad medullary rays can be seen with 

 the naked eye : in the cut surface the broad rays and the phloem 

 zone can be seen clearly, but the growth-rings and the vessels 

 are too fine to be detected with the naked eye. 



TOPOGRAPHY OP THE STEM. The pith was central and appa- 

 rently nearly circular. The stem was broken through the middle 

 before cutting (text-fig. 87), so that fragments only of the pith 

 remain. Tho primary ivood does not form very pronounced 

 bundles round it. The secondary wood is very small-celled and 



Text-fig. 87. Aptiana radiata, Stopes. Transverse section of the stem, 

 X If diameters, showing the rays. The black zone at p. is phloem ; 

 m. t the granular matrix. After Stopes. 



remarkably uniform in structure. Growth-rings are clearly 

 recognisable, but, as they do not strikingly disturb the arrange- 

 ment of the elements, the limits of some of the outer rings are a 

 little uncertain. There appear to be 28-30 growth-zones in 

 the wood, averaging about *6 mm. thick. The vessels are small, 

 and generally arranged so as not to disturb the regular radial 

 sequence of the wood-fibres. The vessels are nearly all isolated, 



