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VI. On Polystelic Boots of certain Palms. By B. G. CormacK, M.A. 

 [Communicated hy D. H. Scott, F.B.S., F.L.S.) 



(Plates XIX. & XX.) 



Bead 6fch February, 1896. 



It is a striking fact that throughout the vascular plants, however great the differences 

 in the reproductive system and in the vegetative shoot, there is, nevertheless, a general 

 sameness in the form and structure of the root. 



This uniformity which characterizes the root is ultimately to be correlated with the 

 uniformity of its function and environment. Botany and zoology alike afford many 

 illustrations of the correlation between fixity in highly symmetrical environment and 

 radial symmetry. 



Van Tieghem made the root a starting-point for study of the symmetry of vascular 

 plants, and has arrived at a new classification of tissues, involving the morphological 

 conception of the stele. His views on the subject are now common property of 

 botanists. His description of the polystelic condition of stems of Pteridophyta and of 

 certain Sperma^hyta has thrown a new light upon structures which were previously of 

 a very puzzling nature. Roots, however, show, almost without exception, one normal 

 central vascular cylinder or stele. Two exceptional forms are recognized and classed as 

 polystelic, certain tuberous roots belonging to the Cycadacea3 and LeguminosaB respec- 

 tively ; and with polystelic roots must be classed certain abnormal Palm-roots now to be 

 described. 



The investigation was carried out on material from the collection made by Professor 

 Bower in Ceylon, supplemented by specimens obtained during the re-potting of Palms in 

 the Botanic Gardens of Edinburgh and Glasgow. 



Thin normal roots of Areca Catechu, Linn., about 2 milLLm. thick, show a central stele 

 of small diameter as compared with the thickness of the cortex. The proportions are 

 indicated by PI. XIX. fig. 1. The piliferous layer is, at least in places, cuticularized. The 

 underlying cells of the cortex are sclerotic, forming an outer zone without intercellular 

 spaces. Prom this there is a transition to an inner, thicker, more parenchymatous 

 zone traversed by thick- walled sclerenchy ma-cells. The rounded parenchyma-cells have 

 the usual intercellular spaces between them ; but in addition to these air-passages there 

 are large radial rifts in the tissue, which extend between plates of cells twelve or even 

 twenty deep radially. These rifts do not extend inward to the endodermis ; thus the 

 inmost layers of cortical parenchyma form a zone four or five cells thick, showing only 

 the usual intercellular spaces. The endodermis is normal, a continuous zone of cells 

 with stratified, pitted, lignified w^alls, thickened chiefly on the radial, inner-tangential, 



SECOND SERIES. — BOTANY, VOL. V. 2 R 



