16 MR. R. H. COMPTON : AN INVESTIGATION OF THE 
The root, a long way below the collet, shows four V-shaped groups of 
primary xylem surrounding a pith. The pith dilates as we pass up towards 
the collet, and the xylem becomes more and more tangential. At the collet 
the xylem lies in four tangential groups, forming an almost closed ring round 
the pith; each group has a small median projecting protoxylem. The phloem 
is in four long bands extending between the protoxylems. So far there is no 
difference visible between polar and lateral groups of xylem, but half-way up 
the hypocotyl the distinction becomes clear. Tte four groups have all broken 
into pieces: each polar group consists of two metaxylem bands with an 
isolated protoxylem in between ; whereas each lateral group consists of two 
xylem bands only, the protoxylem having divided with the metaxylem, 
Higher up the hypocotyl the xylems become more diffuse in texture, and 
each breaks up into a number of smaller endarch bundles. Rearrangement 
and fusion take place in the uppermost 5 mm. of the hypocotyl, and each 
cotyledon trace comprises a large median bundle, formed from the polar 
group by fusion in the middle line of the bundles into which it had broken, 
and a pair of broad loose lateral bundles, each derived from half a lateral 
xylem. Thus the cotyledons receive the whole of the vascular tissue that 
has come up the hypocotyl from the root. 
CASSIA. 
The seedlings examined exhibit a very uniform structure, which will be 
described in detail in C. levigata. With this species C. floribunda agrees 
closely : the other species examined have somewhat narrower diameter, and 
reflect this differenee in the fact that the metaxylems of adjoining triads 
fuse laterally ; so that four tangential bands are present in the hypocotyl 
instead of eight, in addition to the four protoxylems. The structure then 
approximates to the Acacia type. | 
The seedlings are epigeal, the hypocotyl being slender, hairy in iis upper 
portion; and the cotyledons being very flat, thin, and leaf-like. A clear 
yellow pigment is present in the tissues, including the root; and on immer- 
sion in spirits the colour becomes purplish brown. 
Except in C. levigata and C. floribunda the cortex of the hypocotyl con- 
tains a narrow zone of small cells, with walls not specially thickened, 
situated one to three layers from the epidermis. These have doubtless a 
mechanical function in virtue of the relatively high proportion of cell-wall 
to lumen, and they may be compared with similar cells in several Mimosoidem, 
though in the latter the walls are sometimes thickened (Albizzia moluccana). 
Tannin-saes are absent. Stout fibres bound externally the phloem groups in 
the hypocotyl. 
The transition in each case appears to be best described as * intermediate- 
low” ; it begins a few millimetres below the external collet, but is completed 
