an archaic type of Seed from the Palaeozoic Rocks. 79 
2. Series of Transverse Sections. 
Before proceeding with the detailed consideration of the various regions 
of Physostoma , the general relations of its organization may be illustrated 
conveniently by the photographs of a series of three transverse sections cut 
from a single seed (PL V, Figs. 1, 2, and 3). That I have had the advantage 
of studying this series is due to the courtesy of my friend, Professor 
C. E. Bertrand, of Lille, who, hearing that I was engaged upon Physostoma , 
placed the preparations in my hands for investigation. The sections, which 
are numbered M.H. 369, 370, and 371, traverse the chalaza, the middle of 
the seed, and the apical circlet of tentacles, respectively. They belonged to 
the collection of the lamented Maurice Hovelacque, a botanist of marked 
versatility, who had already made valuable contributions to the knowledge of 
our English Coal-Measure plants at the time of his death in 1898. The 
nodule was doubtless derived from one of our Lancashire localities, whilst 
the preparation of the sections (carried out with exquisite perfection of 
technique) was entrusted by the collector to the lapidary, E. Rousseau, 
of Paris. 
The value of the series depends on the fortunate conjunction of excel- 
lence of tissue-preservation with a minimum of displacement in the several 
zones. It is true the layer of epidermal hairs is indifferently preserved, but 
this defect can be repaired from a host of other sections. 
The wall of the seed shows three conspicuous zones, viz. : (1) The 
integument, extending down to, and including, the vascular strands ; (2) the 
nucellus, chiefly characterized by the zone of secretory sacs ; (3) the tapetal 
lining, abutting on the embryo-sac. 
The main features of the three sections are as follows : — 
The lowest section (M.H. 369, PI. V, Fig. 1), cut at a distance of 
•75 millim. from the base, has a diameter of ij millims. (the epidermal 
appendages being excluded). The diameter of the internal cavity is 
•6 millims. It shows the three layers so characteristic of the seed, viz. : — 
(1) The integument, some five or six layers in width. This zone is 
completely separated by a tangentially orientated lacuna (Fig. 1, /) from 
the subjacent zone throughout the upper half of the section, whilst on the 
lower half the separation is incomplete in the radii corresponding to the 
grooves between the ridges. In all, ten lacunae are represented — four below 
and six above — the latter being tangentially confluent. Where the lacunae 
are distinct (i.e. below), the surface of the seed is ribbed, where they are 
confluent the ribbing is obscure (i. e. above). The inner margin of each 
lacuna contains the vascular strand belonging to its rib (PI. V, Fig. 1, v. b.). 
Moreover, the tangential intervals between the neighbouring bundles are 
somewhat smaller on the lower than on the upper half of the section. 
Evidently the section is slightly tilted, the lower half in Fig. 1 corresponding 
