SEEDLING STRUCTURE IN THE LEGUMINOSÆ. M 
TERMINOLOGY. 
The terms collet and external collet are used for descriptive purposes in the 
sense in which the latter is employed by Sterckx (1900, p. 75); i. e. as signi- 
fying the line of junetion between the piliferous layer and the epidermis 
proper. 
The word hypocotyl is used to indicate that part of the axis between the 
cotyledonary node and the external collet. (See p. 90.) 
By the term transition, as technically employed in this paper, is understood 
the changes which occur in the disposition of the vascular tissues only: the 
phenomena exhibited by other tissue-systems are outside the scope of the 
present study. 
Parr А. 
DETAILED DESCRIPTION. 
МІМОУОІрЕ Д, 
ACACIEL.E. 
ACACIA. 
Four species of this large genus have been examined, and all show close 
similarity in form and structure, with slight differences in detail. The ger- 
mination is epigeal: the seedlings are comparatively slender, the cotyledons 
slightly thickened and early falling off. At the base of the hypocotyl just 
above the insertion of the primary root isa prominent ring or collar consisting 
entirely of cortical parenchyma with no special vascular system. This collar 
is concerned in the fixation of the seedling in the soil and in its extrication 
from the testa (Klebs, 1885, p. 544). It is present in many other Mimoseze 
and also in certain Ceesalpinioidese and Papilionate (e. g. Mimosa pudica, 
Leuccena glauca, Petalostylis labicheoides, Sesbania aculeata). The diameter of 
the hypocotyl given in the table is taken immediately above this collar. 
ACACIA DORATOXYLON, A. Cunn. (РІ. 2. figs. 18-23.) 
Tall shrub or small tree. Cotyledons oblong-ovate, slightly thickened. 
The root contains a solid tetrarch xylem star, the protoxylems being equi- 
distant (fig. 18). The phloems are characterised by the presence of a central 
group of clear cells with scanty contents, but not fibrous ; the more densely 
protoplasmic tissues lying on either side of this group. Similar histological 
structure is exhibited by the phloem of the other Acacia spp. examined. 
A parenchymatous pith begins to appear a few mm. below the external 
collet (fig. 19), and dilates rapidly, forcing the xylem into a tangential 
position. At the level of the collar the xylem is in the form of a closed ring 
1-2 cells thick, enclosing a large pith, the protoxylem forming four projecting 
corners (fig. 20). 
