Davey. — Seedling Anatomy of certain Amentiferae . 595 
in the upper part of its hypocotyl replaced by diagonal tetrarchy in the 
root, a transitory hexarch stage being suggested in the intermediate region. 
Cruciform tetrarchy is found in Carpinus and in Corylns. In the latter 
seedling the intercotyledonary poles are connected in part with plumular 
strands, but not to so marked an extent as in certain J uglandaceae. 
Hexarchy is the fundamental arrangement in the hypocotyl of Quercus 
and Castanea , but in the latter genus additional units are present which are 
probably related to plumular leaf-traces. 
Throughout the group the early plumular leaf-traces show double 
structure in both epicotyl and hypocotyl. In the epigeal forms this 
usually applies only to the first pair of leaves, and in their case secondary 
thickening ensues so early that very little primary tissue is differentiated. 
In the hypogeal forms the growth of the plumule is so rapid that the traces 
of several leaves may be present at the cotyledonary node. These may 
extend into the hypocotyl and root, bearing the same relation to root poles 
as the cotyledonary double bundles. 
Urticales. 
In this cohort only a few forms have been examined. All of them 
possess epigeal seedlings which differ considerably in size. Their anato- 
mical features show striking uniformity. 
Ulmaceae. 
Celtis australis and C. occidentalis. These are moderately robust 
seedlings. The cotyledons possess a central double bundle, and transition 
is in accordance with the diarchy type. 
Moraceae. 
Morns alba . The seedling is small and slender. The hypocotyl and 
root are diarch, transition taking place at a high level. 
Maclura aurantiaca possesses a much more robust seedling, resem- 
bling those of the species of Celtis . Transition follows the diarch type. 
Urticaceae. 
Urtica cannabina has a small diarch seedling very similar to that of 
Morus alba. 
Urtica dioica , P arietaria officinalis , and Humulus Lupulus, described by 
Chauveaud , 1 all conform to the diarch type. 
General Remarks . 
Speaking of the vascular structure of the seedlings of Ranales, Rosales, 
and Rhoeadales, Dr. Thomas 2 says that ‘ the hypocotyl shows a varying 
number of primary centres of xylem which alternate with two phloem 
1 loc. cit., p. 295. a 1 0C< c i tj p# 73 2. 
