Mitrospermum compression (Will.'), 
501 
D. The Vascular Tissue. 
The main supply bundle is usually represented only by tracheides. The 
expansion, in which it terminates below the base of the nucellus, consists of 
short reticulate elements (PL XXXIX, Fig. 29). In the basal part of the two 
branch bundles, however, some elongated, thin-walled elements are preserved 
below the tracheides. This tissue is probably phloem (ph. in PI. XXXIX, 
Fig. 27). In the same section from which the figure just mentioned was 
drawn, two small elements with loosely spiral thickenings occur in one 
place on the lower side of the xylem (PI. XXXIX, Fig. 28 ; cf. also Fig. 26). 
They are about 6 /x wide, and are succeeded by larger elements 10/x to 18 /x 
wide, which are reticulate or closely spiral. The phloem is not preserved in 
the part of the bundle where they occur. The small elements have the 
characters of protoxylem, and thus the xylem of the branch bundles, at 
least in the lower part, would seem to have been centripetal in development. 
I have not met with any case of recognizable phloem in the branch bundles, 
after they have emerged from the shell, and curved upwards towards the 
micropyle. The most striking feature of the strands in this part of their 
course is the extreme flattening which they undergo in the principal plane 
of the seed, so that the bundle is better described as a tracheal plate. 
A transverse section in Dr. Scott’s Collection 1 shows one of the bundles as 
a chain of tracheides, twenty elements long in the plane of flattening, but 
only from one to three elements wide (PL XXXVIII, Fig. 20). 
IV. Nomenclature. 
A. Specific Name. 
In his original description of the seed under discussion, Williamson 2 
wrote, ‘All the specimens agree in giving to this species much of the general 
dimensions and contour of the Cardiocarpum acutum of Lindley and Hutton, 
and of the C. Lindleyi of Mr. Carruthers, excepting that the latter observer 
describes his seeds as having a central longitudinal ridge, which my 
specimens certainly have not. Since these differences exist, it may be well 
to distinguish my type under the name of Cardiocarpon compression .’ It 
seems, however, that Williamson was mistaken in entirely denying the exis¬ 
tence of a ‘ central longitudinal ridge since many transverse sections which 
seem undoubtedly to belong to his type show a slight median ridge on the 
surface of each valve in the secondary plane (Text-fig. 2, C, and PI. XXXVII, 
Fig. 10). In fact one of Williamson’s type sections 3 shows a distinct 
indication of a ridge, though this is rather minimized in his drawing of it. 4 
1 D. H. S. 2428. 
3 W. 1409. 
2 Williamson ( 77 ), p. 259. 
4 Williamson ( 77 ), PI. XV, Fig. 124. 
