82 Oliver —On Pkysostoma elegans , Williamson , 
secretory zone , with its now extended perimeter, has thinned out 
considerably. In the inter-fascicular portions of its course, it shows only 
a single layer of secretory sacs, whilst beneath each bundle it expands to 
form a longitudinal cushion in which two ranks of secretory sacs are usually 
present. It is thus evident that the sacs undergo a rearrangement in the 
body of the seed ; in the previous section their maximum occurrence 
coincided with the inter-fascicular radii ; here, the reverse is the case. 
The elements of the tapetal zone are seen more clearly in this section 
than in any other that has come under observation. As in the preparation 
M.H. 369, the cells are thick-walled and tangentially elongated, but there 
is less radial compression of the layers as a whole. The outmost of the 
five layers which it comprises shows clear continuity with the dark rim 
which marks the inner border of the secretory zone (PI. V, Fig. 2, tp.). The 
successive layers of the tapetum show evidence of having been laid down 
in radial series, though, perhaps in consequence of encroachment by the 
prothallus within, the radial files have undergone a certain amount of 
displacement. 
What may be regarded as the delicate prothallus — very rarely preserved 
in Pkysostoma — is seen in this section lying contracted in the cavity of the 
seed (Fig. 2 f ps.). If the membrane which clothes it be the true megaspore- 
membrane, our seed was very different in this respect from Lagenostoma 
Lomaxii and L. ovoides, in both of which the spore- wall was robustly 
developed. 
The third sectio 7 i of the series cuts the seed at the apex and is slightly 
tilted in the same sense as its fellow-sections (diagram, p. 80, M.H. 371 ). 
The plane of section falls above the conical apex of the prothallial cavity, 
the central body of the photograph (PI. V,Fig.3, /.)> being the epidermal shell 
of the pollen-chamber. The arms towards the lower side of the photo- 
graph — of which one (on the left) has slipped out of the circlet — are cut 
transversely, and show the epidermal hairs on the peripheral side in approxi- 
mate longitudinal section. In the upper part of the photograph the arms 
have somewhat greater radial and tangential dimensions, and the epidermal 
processes have a multiseriate arrangement — appearances that arise from the 
fact of the tentacles on this side being cut obliquely, and somewhat nearer 
to the level of their insertion (cf. diagram, p. 80). 
Except when clothing the outwardly directed (abaxial) surfaces of the 
tentacles, the epidermal cells are without tubular processes and have black 
contents ; the epidermis reaches its minimum thickness as it traverses the 
inside (adaxial) faces of the arms. 
The filling tissue of the tentacles consists of a thin-walled, closely-fitting 
parenchyma which is incomplete towards the inside in consequence of the 
breaking-down of the vascular strands. Secretory sacs are absent from 
the tentacles. 
