Mellor: The Seedling Structure of Dryas octopetala. 311 
were extended to the seedlings of Monocotyledons and Dicotyle- 
dons, some further light might be thrown on their origin and 
relationships, the elaborate researches of Miss Sargant (1) being 
directed especially to the origin of Monocotyledons. 
Attention was paid mainly to orders and genera which were 
believed to possess primitive characters. Among the Dzuco- 
tyledons, after examining a number of seedlings, Miss Thomas 
decided that the tetrarch type was characteristic of the Legu- 
minose@, Rosacea, Euphorbiee, Aceracee, Balsaminacee, 
“E 
EXPLANATION OF FIGURES, 
1.—Young seedling of Dryas octopetala. 
2.—Older seedling with first foliage leaves. 
3.—Transverse section through bud of seedling. a cotyledons, £ first 
foliage leaf, c, d and e younger leaves. 
4.—Section of hypocotyl. f vascular cylinder, c b bundles from cotyledons. 
5 and 6.—Sections of root with alternating groups of wood (x) and bast (P). 
Malvacee, and occurred in Casuarina and some of the Poly- 
gonacee and Amentifere. Among the Sympetale, it was 
found in the Convolvulacee, Sapotacea, and Cucurbitacee. 
The diarch type was, with the exception of the orders just 
named, characteristic of the Syvmpetale examined, and also of 
the Ranales, Rhe@adales, Urticales, Piperales, Umbellifore, 
while it is found in some Polygonales and Centrosperme. 
From this we see that the Ranales, commonly regarded as 
primitive in many of their characters, have generally a diarch 
type of root, but an intermediate type has been met with, 
having four phlcem groups and two xylem groups in the hypo- 
cotyl. Onthe other hand, the seedlings of Rosace@ examined 
have a tetrarch root. It is to the latter order that Dryas 
octopetala belongs, and an examination of its seedling shewed 
1gii Sept. 1. 
