BY JOHN MCLUCKI 



297 



narrowest radial intercellular spaces. The cells have thin walls which are 

 strengthened by means of spiral thickening fibres such as are characteristic of 

 the tracheidal cells of the roots of many aerial Orchids. These fibres enclose 

 meshes of varying width. No starch occurs in the cells, which have the general 

 appeai'ance of an aqueous tissue. This zone may be designated as the "sheath" 

 or velamen (Text-fig. 11). In certain cells of the sheath there occur numerous 

 fine hyphae which pass through from the periphery of the root, where they are 

 abundant in the surrounding soil. In this zone the hyphae do not mass in the 

 oells as in other cells of the root, but appear to take the shortest course from 

 the surface to the internal storage cells of the root. Branching of the hyphae 

 is infrequent. These hyphae are connected to others in the adjacent humus in 

 which the root is embedded; occasional tangles of hyphae occur on the root 

 surface from which distributing branches develop into and through the sheath 

 (Text-fig. 1). 



Text-fig. 



-A transverse section of the root of Dipodium punctatum, 

 showing internal anatomy and the distribution of the 

 endophytic fungus (x 15). 



Within the sheath there is a very regularly developed exodermis. The cells 

 of this layer are elongated radially and the outer walls are strongly suberised. 

 Thin-walled passage cells occur at frequent intervals, and these are very much 



