Spratt , — Some Anomalies in Monocotyledonous Roots. 103 
simple oval pits for the most part, but occasionally annular thickening ; 
(2) air-spaces surrounded by slightly elongated parenchymatous cells with 
contents, i.e. phloem elements (see PI. Ill, Fig. 10). In the internal 
bundles of Pandanus the phloem elements surround air-spaces. 
Externally there is a slight peculiarity to note about Monster a. The 
young root has a spongy-looking covering, this is followed by a smooth 
region, and finally we have another spongy one. In the young root 
there are two very distinct prismatic layers externally. The outer one is 
slightly lignified and long, blunt, unicellular hairs grow out from it (see 
PI. Ill, Fig. 11). These hairs fail to give any suggestion of blue coloration 
with either chlor-zinc-iodine or iodine followed by sulphuric acid, but are 
coloured slightly yellow by an acid solution of aniline sulphate and 
red by an acid solution of phloroglucin, indicating lignification. In 
the smooth region the peripheral tissue consists of a cambium which 
forms thick-walled, brick-shaped cells, suggesting cork, but they very 
definitely give the lignin reactions quoted above, and on close examina- 
tion the walls are seen to be pitted. In the older spongy region the 
same blunt hairs reappear, but below them there are layers of brick- 
shaped cells with lignified walls as described (see PI. Ill, Fig. 12). 
It seems probable that during the first part of the growing season the root 
develops hairs, but later ceases to do so, recommencing, however, at the 
beginning of the next season. As the root becomes older the peculiar 
lignified cells are developed below the hairs, which at a later period die 
away, leaving the older part of the root destitute of spongy regions. 
These spongy regions recall the velamen of orchids, which likewise 
gives lignin reactions. In many species of Pleuroihallus groups of hairs 
very similar to those in Monstera arise from the outermost layer of the 
velamen. In Mystacidium infundibulare they appear to arise when the 
roots penetrate a substratum, suggesting root-hairs, except that they are 
lignified. It seems possible that the spongy covering formed by the hairs 
in Monstera root plays a part similar to that of an orchid velamen. 
Raphidophora DEC UR SIVA. The stele of the aerial root of this 
Aroid appears fairly normal. The interior of the radial ring is occupied by 
tracheides pitted as in Monstera , and there is also a ring of large vessels 
placed somewhat irregularly. These have multiseriate, elongated pits. As 
regards the exterior of the root, Raphidophora resembles Monstera in 
having first two definite cell layers and later several produced by a cambium, 
but the hairs persist throughout (see PL III, Figs. 11 and 12). 
Yucca , Monstera , and Raphidophora each possess a band of very thick- 
walled sclerenchymatous cells just outside the stele, which are in each case 
pitted. In Yucca they resemble tracheides in shape ; in Raphidophora there 
are some tiacheide and some parenchyma-like ; and in Monstera they are 
all parenchyma-like. 
