152 REY. PROF. G. HENSLOW ON THE 
vascular cords which have their tracheæ on the inner side, 7. e. 
facing the medulla, and the phloém on the outside of it, i. e. 
facing the cortex, as indicating an axis; but when the circle is 
broken up and these two elements of the cords are altered or 
reversed in position, as they often are in the placentas of a carpel, 
he then pronounced them to be “foliar.” This latter condition, I 
think, is undoubtedly true; but he does not, however, appear to 
have noticed that they are very far from being absolute distine- 
tions. Thus, in his figure of the anatomy of Campanula medium 
(op. cit. pl. 12. figs. 69, 70) there is an apparently truly axial 
cylinder; but the bases of the ovary-cells are present; and in 
fig. 72 the cords facing the septa constitute an “axial” ring, 
while those facing the placenta have the trachez reversed. Again, 
in his figure of Balsam (pl. 10. fig. 34) there are five cords 
oriented and symmetrically arranged in a circle as if axial, but 
the dorsal cords of the carpels are already differentiated. Now 
this latter condition of things is not at all infrequent. If the 
reader will turn to my figures as follows :— Reseda Qx. 5; PL 
XXIV.), Dianthus (x. 8; Pl. XXIV.), Silene (x1. 7; Pl. XXV), 
Sedum (xxvu. 4; Pl. XXVIII.), Azalea Gr 6; PL XXIX 
Digitalis (xum. 7 ; PI. XXX.), it will be seen that the cords are 
still arranged more or less accurately as if axial; but they are 
nevertheless carpellary, as the distinction between the dorsal and 
placentary cords is already pronounced *. 
With reference to the relative positions of the tracheæ and 
phloém, it is an extremely common occurrence for the med ullary 
and other cords to have the tracheæ either accurately localized in 
the centre ofa eylinder of phloém, asin Primula, or else scattered 
irregularly throughit. I have no hesitation in saying that these 
latter arrangements are the predominating ones in all floral 
structures. Moreover, the methods of change of position of the 
trachez of a cord from an internal to a central or external 
position are not always the same, as I shall explain later on. 
Of this kind of research I am only acquainted with M. Ph. 
van Tieghem’s work as being anything approaching a general 
consideration of the subject, with the sole exception of the 
order Orchideæ; for this has been somewhat specially treated 
* Fora further discussion on the orientation of cords &c., I would refer 
the reader to my work, ‘The Origin of Floral Structures’ (Int. Scr. Ser., LXIV.), 
p. 71 &e. 
