BOTANICAL SOCIETY OF EDINBURGH 63 



the approach of the arms cutting through the neck of 

 cortex which joins that inside to the surrounding mass, 

 and, finally, the disappearance of this central portion of 

 cortex and inner ring of bundle-sheath. 



II. The bundle-sheath in the petiole and rhizome does 

 not appear as a cortical layer similar to the bundle-sheath 

 (endodermis) of roots, since the cortical cells do not lie 

 opposite the cells of the bundle-sheath, but seem to form 

 part of the bundle itself ; it, however, shows the characters 

 of the typical endodermis, with dark dots on the radial 

 walls, and no intercelkilar spaces. The inner layer of the 

 cortex is not differentiated from the other cortical layers. 



III. The layers of cells internal to the bundle-sheath 

 are derived from it by division of its cells, and these 

 divisions begin at a short distance below the apex, but do 

 not form a pericycle. 



IV. The spore of the Mcrtensias is reniform ; round and 

 marked with a triradiate line in the Engleiclicnias. 



I consider that the differences in spores, petiolar bundles, 

 general growth and appearance of the plants, justify the 

 greater distinction formerlv made between the Mcrtensias 

 and Engleichenias, when they were considered as different 

 genera, and that these characters are sufficient to prevent 

 the two genera being classified as merely sections of one 

 genus. 



MORRISON AXD Gllil! LIMITED, I'UIXTERS, EDINBURGH. 



