Transition from Stem to Root in Palm Seedlings. 65 
changes in the xylem groups. Careful comparison of several 
series of sections has, however, rendered the main points clear. 
Pritchardia sp. (Fig. 9). 
The transition is in all respects similar to that in Livistona 
mauritana. The ground-parenchyma of the cotyledon stalk and 
sheath is throughout dense, and no trace of a cuticularized ring 
round the bundles was anywhere observable. 
Fig. 9. Pritchardia sp. Fig. 10. Colcospadix sp. 
Coleospadix sp. (Fig. 10). 
The transition appears to be of the same type, but the very 
short curved stalk of the cotyledon, and the advanced age of the 
seedling rendered examination very difficult. 
Two points brought out above require a little further consi¬ 
deration. 
In the first place there is the question of the cuticularized 
layer surrounding some of the bundles in the cotyledon stalk of 
Phoenix dactylifera , L. and Livistona mauritana. This sheath in its 
cuticularized state can only be detected in that short portion of the 
stalk where there is a rich development of air-spaces. That the 
function of the endodermis is to cut off the bundles from the 
external air has long been suspected. The rich development of 
aerenchyma in the roots of many aquatics is frequently accom¬ 
panied by the presence of a well-developed endodermis, and indeed 
