YamPOLSKY : Siiidy of OU palm. 



137 



Text Figure 55. 



A — longitudinal section through a mature pneumathode X 12; 

 B — portion of root witli two piieuniathodes — one just enierging thie otlier inatureXS. 

 C — a mature pneumatliode part of aerenchvnia slougiied off showing centrai 

 bundleX 10. 



In text Figure 55 B two such pneumatliodes are seen on a portion of a root. 

 The one to the right is fuliy mature, the one to the left has just broken through 

 and in its appearance looks like a secondary root, hi their origin they do not 

 differ froni a secondary root an Figure 53 Plate VII may very well serve as an 

 early atage of development of that organ. Such a root in cross-section shows in 

 the center a single vascular bundie mostly occupied by thick-walled bast cells 

 and witii xyiem cells towards the periphery. Surrounding the bundie is a 

 layer of parenchyma cells — this is followed by a spongey pareiichyma, 

 then again a zone of parenchyma, and finally the epidermis. In the older 

 structures the epidermis dégénérâtes a strong hypodermis is developed and 

 bast cells almost completely occupy the outermost zone of parenchyma. 



When the pneumathode is mature, the epidermis and hypodermis at 

 the tip, split and thèse are reflexed giving a vase shaped appearance to 

 the structure. In text Figure 55C such a structure is seen. Hère the central 

 bundie stands out above the aerenchyma tissue as a resuit of the sloughing 

 off of some of the tissue. In Figure 55A a longitudinal section shows the 

 various layers. The hypodermis in the figure is represented by a thick 

 line on either side where it energes from the larger root. As we hâve 

 already stated, the cells of the aerenchyma are more or less stellate in form. 



Such a spongey structure offers an excellent means for gas exchange 

 and the présence of the air chambers in the larger root, allows for a very 

 efficient System of aération. The thick hypodermis and the woody character 

 of the older root in gênerai would allow practically no movement of gases 

 from within, out and from without, in. With the pneumathodes in commu- 

 nication with the air chambers within the root the plant is adapted to 

 withstand long submersion under water. 



The fi[ier détails of the structure of the organ, its development and 

 modifications hâve been reserved for another contribution. However, in 

 the main the pneumathode (excepte for its outward appearance) agrées 

 with the so called structure found in palms by JOST (1. c). 



