280 ME. B. G. CORMACK ON POLTSTELIC 



into sclerenchyma ; and corresponding with the continuous change to the single large 

 stele, there is a gradual change to the complete endoderraal system of the normal root. 



The changes just described seem best explained by assuming that in successively 

 younger portions of the root the apical meristem has continuously changed its mode of 

 differentiation. 



With regard to other Palm-roots examined, roots of Cocos niicifera, Linn., were found 

 showing, in all essential points, correspondence with the roots of Areca just described; 

 the sclerenchymatous development was even stronger than that of Areca. 



The very thick root of Verschaffeltia splendida, H. Wendl., available for examination 

 showed an extraordinary degree of complexity represented diagrammatically in PL XX. 

 tig. 14. The diameter of the diagram is twice that of the root. Pig. 15 shows one of the 

 perfect steles — the stele indicated by st. in fig. 14 ; the magnification and scheme of 

 lettering and shading are the same as in jBgs. 7, 8, 9. Pig. 14 indicates, so far as 

 the very small scale will admit, the result of observations made under the same 

 magnification as figs. 7, 8, 9. 



Hoots of other Palms were examined with the following result : — 



Type Four. Seafortkia elegans, R. Br, [Ptychosperma elegans, Blume). 



Type Three. Dypsis, sp. 



Euterpe edulis, Mart. 



Type Two. Ptychosperma filifera, H. Wendl. 



Ptychosperma Cunninghamii, H. Wendl. 



Hyophorbe Verschaffelti, H. Wendl. [Areca Verschaffelti, Hort.). 



Kentia Fosteriana, F. Muell. 



Caryota sobolifera, Wall. 



Geonoma pumila, Lind. et H. Wendl. 



Corypha australis, K. Br. 



Livistona chinensis, R. Br. 



Phoenix dactylifera, Linn. 



Phcenix sylvestris, Roxb. 



As the range of specimens available for examination was very limited, it by no means 

 follows that the degree of complexity just noted is the maximum for each species in 

 question. 



With regard to the physiological aspect of these various types of root-structure, 

 reference has already been made to the correlated prevalence of uniformity in structure, 

 function, and environment among roots ; there remains for consideration the problem of 

 adaptation in a few of its aspects interesting from the present standpoint. 



As a living organ, the root respires and fulfils the special functions of absorption, 

 conduction, insinuation, fixation. The root of a young plant must perform these and 

 other subsidiary duties ; and the problem of adaptation is most complex, involving a 

 combination of delicacy, slenderness, and strength. 



A root-system of an older plant, especially one with marked secondary changes, shows 



