434 DR. ERIC DRABBLE ON THE 
which the cells are more regularly arranged, conforming to the description given by 
Olivier (8) for the internal cortical zones in Monocotyledons. 
Air-spaces. 
The development of the cortical air-spaces was followed in Kenia sp. and in Areca sp. 
The process was found to be exactly similar in each. 
A short distance behind the apex certain cells, usually in small groups of two or three 
as seen in transverse section, lose their contents and present a very refractive appearance 
in their walls (Pl. 48. fig. 18). "These walls sooner or later disintegrate, and in this way 
a lysigenous space is formed (Pl. 48. fig. 19). These spaces enlarge by the disintegration 
of more cells, and their boundaries nearly always present the remains of the partially 
dissolved cells (Pl. 48. fig. 20). 
Various Forms of Air-spaces. 
In Phytelephas macrocarpa (Pl. 48. fig. 21) the air-spaces are always small, even 
in the mature root, being formed merely by the disintegration of 3-10 cells as seen in 
transverse section. These spaces are irregularly scattered throughout the cortex. 
In Kentia sp. (Pl.48. fig. 20) the air-spaces are more extensive and are n 
elongated ; they are very numerous and irregularly scattered. 
In Metroxylon Sagu (P1. 48. fig. 22) they are more confined to the internal zone of the 
cortex, and in Zrartia sp. (Pl. 48. fig. 23) only a single ring of rounded cavities is present 
in the innermost cortical zone, immediately surrounding the endodermis. 
In Phenix sylvestris (Pl. 49. fig. 30) they are very numerous and occupy nearly the 
whole of the cortical region. They are more or less rounded, having individually very 
little radial extension, and are separated from one another only by a single or double 
layer of cells. 
In Caryota australis (Pl. 49. fig. 29) the disposition is similar, but here the remains of 
the disintegrated cells may be clearly seen as diaphragms in the lumina of the air-spaces. 
The same is true to a less extent in .Phænis sylvestris (Pl. 49. fig. 30). In Licuala 
spinosa (Pl. 49. fig. 28) the spaces are radially greatly extended and occur in two rings, 
the spaces of the inner ring being much larger than those of the outer. In Licuala 
gracilis (Pl. 48. fig. 24) there is only a single ring of radially very extensive spaces, 
which extend almost from the endodermis to the tegumentary layers. 
The air-spaces present no resistance to the growth of the surrounding parenchyma, 
and in some cases (e. g., Areca Catechu) advantage is taken of this; some of the 
surrounding cells project into the cavity and there swell and undergo division 
(Pl. 48. figs. 25 & 26), and in this way the air-spaces may become completely filled with 
a secondary tissue. This tissue becomes lignified and pitted and the peculiar condition 
figured i in fig. 27 results. 
Lignified Elements of the Cortex. 
cone all palm-roots possess some lignified elements in the parenchymatous cortex. 
Only in Phytelephas macrocarpa (Pl. 48. fig. 21), Thrinaz parviflora, and the contractile 
ges of er ik umbraculifera was liguitosHon found to be entirely wanting. 
