454 DR. ERIC DRABBLE ON THE 
The work of Tansley and Boodle shows that great irregularity exists in the development 
of these so-called * steles," a single cell sometimes giving rise on division to both “ extra- 
stelar " and “ intra-stelar " tissue. 
Important evidence has recently come to hand in a memoir by Schoute, entitled * Die 
Stelàr-Theorie, where he shows that even in the stratified apices of Phanerogams no 
hard-and-fast line can be drawn between the products of the various layers. 
It thus becomes more and more evident that both in stem and root we have to deal 
with a common parenchymatous ground-tissue, through which run strands of xylem and 
phloem, usually accompanied by fibrous tissue, often in the form of sheaths—xylem, 
phloem, and fibres being all developed from the procambial tissue. This last sometimes 
arises in the form of separate strands in the stems of so-called “ polystelic " Pteridophyta 
and in stems of Dicotyledons and Monocotyledons, each strand giving rise in the former 
case to a “stele” and in the latter case to a “bundle.” Thus it appears that the 
* bundle" in a dicotyledonous stem and the “stele” in a “polystelic” fern arise in a 
precisely similar manner, whereas the “stele” of a dicotyledonous plant and the “ stele ” 
of a “ polystelic " fern are, from the developmental standpoint, very different structures. 
In other cases the procambial tissue takes the form of a single central strand, as in 
* pithless " roots and “ protostelie " ferns, or of a hollow cylinder in roots with pith, 
while in yet other cases—for example, the roots of Palms—it may at first appear as 
separate strands, giving place later to a hollow cylinder. 
It remains to be seen how far the results of future investigation will support the views 
expressed above, but at the present time there is great weight of evidence tending to 
show that all ideas of ** monostely "' and “ polystely," and of “ medulla " and * cortex” as 
separate morphological entities, are founded upon an artifical conception of the nature of 
the structures involved. 
My thanks are due to the Director of the Royal Gardens, Kew; to the Director of the 
Royal Botanic Gardens, Ceylon; to Mr. Herbert Wright; to Professor Bower; and to 
Professor F. W. Oliver for the material on which the present investigation has been 
carried out; and particularly to Professor Farmer for his kind and unfailing interest 
and valuable criticism during the progress of the work. 
BIBLIOGRAPHY. 
(1) Mont, H. vox.—Vermische Schriften. Tübingen, 1845. 
(2) Karsten, H.—DieVegetationsorgane der Palmen. Abh. Berl. Akad, Wiss. (Phys.) 1847, pp. 73-236. 
(3) Náaxur, C. vos.— Beitrüge zur wissenschaftliche Botanik, Heft i. Leipzig, 1858. 
(4) Russow, E. A. F.— Betrachtungen über das Leitbündel- und Grundgewebe, u. s. w. Dorpat, 1875. 
(5) FarkreNnEnG, P.— Vergleichende Untersuchungen über den Bau der Vegetationsorgane der Mono- 
cotyledonen. Stuttgart, 1876. 
. (6 Dr Bary, H. A.—Vergleichende Anatomie der Vegetationsorgane der Phanerogame und Farne- 
- Leipzig, 1877. 
D Vax Tırcenem, P. E. L.—Recherches sur la symétrie de structure des plantes vasculaires. Ann. 
Sei. Nat. sér. 5, xiii. (1870-71) pp. 5-314, pls. 3-8. 
(8) Oueren, L.—Recherches sur l'appareil tégumentaire des racines. Ann, Sci. Nat. sér. 6, xi. (1880- 
| "n pp. 5-133, pls. Am oo: 
CH 
