158 REV. PROF. G. HENSLOW ON THE 
phloém on the outer part of the wedge-shaped cord, as seen in a 
transverse section. There may be an indentation on the phloém, 
thus giving a cordate appearance. This indicates a preparation 
for chorisis. When the cords pass into the floral receptacle, the 
tracheæ begin to lose their precise arrangement, first, by spreading 
laterally and by multiplying the trachex by radial chorisis. The 
latter then often become central within a circular phloém ; or, if 
this be oval or irregular in outline, the tracheæ are dispersed 
throughout it. 
Thus when they form the ribs and veins of petals, the cords are 
mostly cylindrical *, with the tracheæ central. When, however, 
they are destined to supply the margins of the carpels and thence 
to send off branchlets to the ovules, a section shows great irregu- 
larities; while the tracheæ may pass from one, the inner, side of 
the phloém to the outer, i. e. facing the ovary-cell. The appear- 
ance of a circular ring of cords being axial is of course heightened 
when there is a central medulla within the circle of cords. As 
soon, however, as the medulla vanishes by the gradual eonstrie- 
tion of the vaseular cylinder, then M. van Tieghem considers 
the axis to be extinct. This, as a rule, takes place at least as 
soon as the level of the lowest ovules is reached. 
Now, every earpel is theoretieally, and indeed normally, pro- 
vided with three cords, one dorsal and two marginals or pla- 
centary. If the pistil have an axile plaeentation, then all the 
pairs of marginal cords may be grouped round a central medulla 
as if axial, and the trache:e may or may not be oriented inwards f. 
The three cords have branched from a common stem below ; and 
I would regard the point where they have thus separated as the 
termination of their axial existence, and at least would call 
them potentially foliar, although the tracheæ may still remain 
facirg the centre. 
In Hellebore and Eranthis (iv. 4; Pl. XXIII.) the carpels 
are, so to say, already sketched out in the receptacle before 
they become actually free from each other; and although the 
marginal cords have their tracheæ oriented inwards, the tbree 
* Some of them in the corolla-tube of Honeysuckle (xxxrr. 6; Pi. XXVIII.) 
are decidedly wedge-shaped. Sedum Telephium (xxvu.4; Pl. XXVIII.) forms 
a complete cylinder within the ovary-cells ; but it really represents placental 
cor ls, as the dorsal cords are present. 
t They are so in Sedum (xxvi. 4-6; Pl. XXVIIL); but the tracheæ are 
central in Primula (x11x. 8; Pl. XXXI.). 
