136 Bulletin Jard. Bot. Buitenzorg, Série III, Vol, V. LivR. 2. 



of the root cap, suggesting perhaps periods of accelerated growth alternating 

 with periods of protracted growth (Figures 123 and 126 Plate XV). Figures 

 122, 124 and 125 Plate XV show the branched character of thèse aerial 

 roots. In Figure 121 an unusually large root cap is seen. 



Secondary roots from thèse adventitious roots develop in the usual 

 way — occasionally they begin to develop when the hypodermis of the mother- 

 root is too résistant and cannot be pierced and so they are forced to grow 

 down the iength of the root within the space enclosed by the hypodermis, 

 emerging at a point where the résistance of the hypodermis can be overcome. 

 Such a condition is shown in Figure 124. 



Figure 115 Plate XIV is a sector of a cross-section of an adventitious 

 root in which differention has advanced to almost a complète stage. The 

 epidermal cells however are still intact even though the hypodermis is quite 

 fully developed. The changes that hâve taken place can be best seen by 

 contrasting figures 114 and 115. The parenchymous cells of the septa or 

 lamellae hâve remained unmodified throughout although an occasional 

 schlerenchymous cell develops hère and there (Figure 115). When the root 

 dies only the cells of the septa degenerate so that it is quite characteristic 

 for such roots in a dead condition to separate into distinct éléments, a 

 tubular shell composed of hypodermis and bast and within that shell the 

 rest of the root tissure which includes everything within the endodermis and 

 the zone of cells which hâve gone over into a schlerenchymous ring 

 shown in Figure 1 15. 



The absence of root hairs and the early development of an hypodermis 

 limits the absorptive area to the région of the growing point. The condition 

 in the oil palm root agrées with the observations of COPELAND (^) on the 

 coco-nut palm. Water absorption is maintained through the epidermis near 

 the tip. In Cocos this région according to CoPELAND extends 5 cm. from 

 the tip, the région beyond is occupied by the hypodermis. In droughtthis 

 hypodermis grows quite close to the tip (2 cm.). 



The pneumathodcs. 



The second group of secondary roots consists of the pneumathodes 

 which are distributed every where on the roots both on the nutritive and 

 adventitious roots. 



The structures occur normally upon the roots of the oil palm and 

 there can be no doubt that they are associated with aération. The pneuma- 

 thodes appearing on the adventitious roots are shorter and broader than 

 those appearing on the undergrond roots. On the underground roots they 

 are longer and narrower. Except for their somewhat smaller size the 

 pneumathodes are like those found on the roots of the coco-nut palm. 

 Many of the palms in the collections growing in the Oardens at Buitenzorg 

 show simillar structures. 



