438 DR. ERIC DRABBLE ON THE 
does not take place. It is probable that the walls of the original sac become mucilaginous 
and disappear in the old root, and that the bundle of raphides, with its enclosing 
mucilage, does not occupy a cell at all, but rather an intercellular space which may 
become enlarged to any extent by growth of the surrounding elements, 
Endodermis. 
Round the normal cylinder the endodermis forms a complete circle. In the roots with 
a lobed cylinder the endodermis follows the contours of this, and in those cases in which 
the cylinder is made up of a series of separate strands the endodermis is well developed 
on the peripheral surfaces, but internally is lost, becoming merged into the general 
ground-parenchyma, except in a few cases, e. g., Areca sp., where a complete endodermal 
investment surrounds one or more of the strands. i 
The endodermis is composed of a single layer of cells, except in Jriartia and Kentia 
(P1. 49. fig. 48), where local doubling was observed. The constituent cells are generally 
3-6 times longer than broad (Pl. 49. fig. 46), but in contractile roots of Corypha 
umbraculifera they are short and square. 
Occasionally, as in Sabal Palmetto, Areca Catechu, Hyphene thebaica, and Latania 
Loddigesii, the cell-walls are composed of cellulose; in contractile roots of Corypha 
umbraculifera they are cuticularized, but much more commonly they are lignified. 
In Plectocomia elongata the walls are very slightly lignified ; in nearly all cases, how- 
ever, all the walls except the external tangential are densely lignified and thickened in a 
manner recalling that of the cells composing the fibrous layer of an anther, as first 
pointed out by Von Mohl (1) (Pl. 49. fig. 46). The internal wall is uniformly thickened 
and deeply pitted. From this extend bands of thickening on the radial walls, while the 
external walls are usually not thickened or only very slightly so (Pl. 49. figs. 45 & 47). 
This condition obtains in Phenix sylvestris (Pl. 49. fig. 30), Licuala gracilis (Pl. 48. 
fig. 24), Licwala spinosa (Pl. 49. fig. 28), Livistona oliveformis (Pl. 49. figs. 45 & 46), 
Kentia (Pl. 49. fig. 47), and in the majority of palm-roots. 
In Raphia Ruffia the thickening is almost equally deposited all round, the external 
tangential walls being thickened, and in Metroxylon Sagu the lumina are almost 
obliterated. 
Non-lignified passage-cells are generally wanting, but occasionally occur. In Phenix 
sylvestris they may occur at any point. In Kentia (Pl. 49. fig. 47) two or three may occur 
together, generally opposite the protoxylem. 
The process of lignification of the endodermis was followed in Phenix reclinata. There 
is a tendency for it to commence opposite the phloem-groups, but this is by no means 
invariably the case. Usually several cells in contact, forming a tangential row, undergo 
lignification at the same time, their lateral neighbours being at this time quite unaltered, 
although they may later all undergo complete lignification, the mature root in this 
species showing no passage-cells. 
A peculiar condition was observed in the endodermis of Corypha australis and the non- 
contractile roots of Corypha umbraculifera, some cells being cuticularized, while the rest 
were lignified. 
