436 DR. ERIC DRABBLE ON THE 
spherical rough body, which almost fills the cavity and consists mostly of compounds of 
silicon.” 
In the Palms examined these stegmata have only been found in connection with the 
Raphia-type of fibre (Pl. 49. figs. 37 & 32, steg.). In general they agree very well with 
De Bary’s description, but the body of the roughened inner wall, though showing some 
silification, also appears to be rich in calcium oxalate, as might be expected, when it is 
remembered how constant is the association of this substance with any rapidly growing 
tissue (apices) or elongating elements (fibres). Percival (19) has recently called attention 
to crystals of calcium oxalate in the cells bordering the developing fibres in Trifolium, 
and it appears certain that this substance is in some way intimately associated with 
carbohydrate metabolism, probably being formed by the precipitation of oxalic acid or acid 
. potassium oxalate in an insoluble form, as believed by Schimper. 
In the above account of the stereome-tissues of the cortex, no mention has been made 
of the association of different types of element, although it is very unusual to find one 
type alone represented. 
Lignified parenchyma occurs alone in Latania borbonica. It is associated with stone- 
cells in Cocos botryophora, Diptothemium maritimum, Bactris minor, Sabal Palmetto 
(Pl. 49. fig. 33), Caryota Rumphiana, and Caryota urens, and with fibres of the Raphza- 
type in Martenezia Lindeniana, M. caryotifolia, Hyphene thebaica, and Plectocomia 
elongata. 
Stone-cells have in no ease been found to occur alone. They are associated with 
lignified parenchyma in the roots mentioned above, and with fibres of the Kentia-type in 
Oncosperma fasciculatum. 
Fibres of the Kentia-type occur alone, both individually and in bundles, in Ptycho- 
sperma perbrevis, and in Actinorhytis Calapparia, where they are of the Kentia-type in 
the external zones, but more definite within. 
Fibres of the Raphia-type occur alone in Dictyosperma album, where they are very 
abundantly developed, and in Metroxylon Sagu. 
In Arenga Wightii lignified parenchyma, stone-cells, and fibres of the Raphia-type 
oceur. 
In the young root of Dictyosperma album a bundle of fibres with two small tracheidal 
elements was found, and in Jriartia sp. each bundle of fibres contains centrally a thin- 
walled element, presenting the appearance ofa young sieve-tube, but it was impossible to 
obtain material of roots in which the development was sufficiently advanced to settle this 
point. De Bary (6) observed the same thing, and says, “in the outer parenchyma...- 
of the cortex .... numerous small bundles of sclerenchymatous fibres lie, each 
enclosing in its centre 1-2 thin-walled elongated elements (perhaps sieve-tubes ?)." 
 Lignifieation in any bundle of fibres commences in the external elements and 
crc towards the centre. 
..— Tn some mature roots the external fibres of any bundle may be fully lignified, while the 
inner elements retain their cellulose walls. 
These results may be summarized as follows :— 
The. kc form of lignified element—namely, the thin-walled pásciqihsoatens cells, 
