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THE SEEDLING STRUCTURE OF 
DRYAS OCTOPETALA. 
A. EVELYN MELLOR, B.A. 
Dryas octopetala is one of the rarer Alpine plants of Britain, 
and in its only station in West Yorkshire, Arncliffe Clouder, 
is well-known to northern botanists. There it occurs in great 
abundance, and its habitat is very characteristic of its occur- 
rence in other parts of Europe. It almost invariably establishes 
itself on overgrown limestone pavements, or on screes that. 
have become fixed by the roots and rhizomes of other species, 
but Dryas itself does not act as a pioneer, nor as an early scree 
binder. In older pavements there is a tendency for it to give 
way before tussock-forming grasses. At Arncliffe it appears 
to be slowly spreading, owing, probably, to the long style, 
which becomes feathery after fertilization, persists in the fruit 
and acts as a means of wind dispersal. 
In the present paper it is intended to deal only with the 
structure of the seedling, which is preliminary to a detailed 
investigation of the life history of the genus, now being under- 
taken by Dr. T. W. Woodhead, to whom I am indebted for 
the materials on which these observations have been made, and 
for help in arranging them for publication. 
Recently much work has been done on seedling structures: 
by Misses Sargant (1), and Thomas (2, 3 and 4), and Messrs. 
T. G. Hill (5), Tansley (2 and 3), and others, with the object 
of determining whether a study of seedling anatomy would 
throw any new light on the problem of phylogeny. 
Miss Thomas, in her paper on the ‘ Theory of the Double 
Leaf-Trace,’ (4), shews that the special point of interest is 
the manner in which the veins, passing from the cotyledons, 
through the hypocotyl, to the root, form the structure charac- 
teristic of the root stele. Ina primitive type, such as a typical 
Cycas, four vascular bundles pass from each cotyledon into 
the root. On their way, the wood and bast of which they are 
composed, become re-arranged in such a way as to give rise toa 
tetrarch root, 7.e., one with four groups of wood alternating 
with four groups of bast. That the Cycads are ancient and 
primitive is generally acknowledged, and the root of a typical 
Cycas is tetrarch. Recent investigations have been made on 
the seedlings of allied groups and their structures compared. 
Amongst Gymnosperms which have two cotyledons, as the 
Taxacee, Cupressine@, and some of the Taxoide@, a bundle 
goes from each cotyledon and gives rise in the root to a cylinder 
composed of two groups of wood alternating with two groups 
of bast, 7.e., a diarch root. It is concluded that the diarch type: 
has been derived by reduction from the more primitive tetrarch 
type. 
It therefore seemed probable that if these investigations 
Naturalist, 
