90 Oliver . — On Phy so stoma elegans , Williamson , 
part of the seed-wall. The salient ribs, of course, overlie the vascular 
bundles, or, more correctly, the lacunae which are constantly found on the 
abaxial side of these strands (PL V, Fig. 6 ; PI. VII, Fig. 28). It is only at 
the base of the seed that these lacunae become confluent tangentially, so 
that the parenchyma-zone of the testa shows complete separation from the 
subjacent tissues. (Cf. p. 81 and PI. V, Figs. 1 and 2, for trans. sections; 
PI. VI, Figs. 21 and 22, for longitudinal sections.) 
Passing from without inwards, except at the seed-base, the tissues 
follow one another as follows : epidermis, with hair-like prolongations on 
the ribs ; parenchyma of integument ; vascular strands ; secretory zone ; 
and finally the conspicuous black-walled zone lining the seed-cavity, which 
may be designated tapetum. 
At the base of the pollen-chamber, where the integument becomes 
free from the nucellus and separates into tentacles, the vascular strands, 
accompanied by their lacunae, bend out slightly and pass into the tentacles- 
The secretory zone does not enter the tentacles — indeed, secretory sacs 
have not been observed either in a tentacle or in the very short united tube 
above the level at which the nucellus becomes free. The secretory layer 
and tapetum, both with much diminished radial depth, pass up to the 
pollen-chamber, clothed externally, of course, by the epidermis which lines 
the sinus (PL VI, Fig. 13). 
These layers form the narrow belt or plinth upon which the pollen- 
chamber is seated. This zone measures -15—2 millims. across ; it is simply 
a zone of nucellar tissue intercalated between the place of separation of the 
tentacles and the bottom of the pollen-chamber. A similar zone is present 
in the full-sized seeds of Lageno stoma Lomaxii , where it is considerably 
more extensive than in Physostonia (-5 millims. across), whilst the slope up 
to the pollen-chamber is quite gentle, instead of being steep, as in the present 
case. 1 (PI. V, Fig. 12,//; PL VI, Fig. 18.) 
4. The Pollen-chamber. 
The general features of this organ have already been outlined in the 
introduction (p. 78). It is a circular chink-like cavity at the apex of the 
nucellus, formed by the separation of the outer layer (epidermis) which 
communicates with the exterior by a small circular orifice situated on 
a low papilla in the axis of the seed (PL VI, Figs. 17 and 18, o.p.c .). The 
extreme dimensions of the pollen-chamber are : Horizontal diameter 
(outside wall to outside wall) i-2mm. ; height (from insertion to orifice) 
1 mm. The corresponding dimensions in L. Lomaxii are -75 mm. and -7 mm. 
The effective cavity of the chamber is restricted to a chink about 37/x 
1 Oliver and Scott, loc. cit., p. 200, 
