an archaic type of seed from the Palaeozoic Rocks. 85 
to an arbitrary boundary such as is obtained by producing down to the 
chalaza the plane of separation of the free regions of nucellus and integu- 
ment. But in Physostoma , as we shall see, the anatomical characters come 
to our aid and leave us no choice in the matter. The following classification 
of regions is followed, whilst the grounds on which it is based will be stated 
in the discussion at the end (p. 106). 
The Integument includes the tentacles and the ribbed investment of the 
seed as far as (but excluding) the secretory zone. The vascular strands 
belong to the integument. 
The Nucellus includes the free apex (of which the peripheral portion 
forms the pollen-chamber) together with that part of the central body of 
the seed which lies within the outer limit of the zone of secretory sacs. 
1. The Integument. 
In the foregoing account we have seen that throughout the body of the 
seed the integument is a ribbed structure fused with the nucellus, whilst level 
with the pollen-chamber it becomes free, at the same time breaking into 
a ring of about ten tentacles arranged to form a loose cone around the pollen- 
chamber. Or, starting at the apex, and tracing it downwards, we have 
a whorl of separate arms which unite laterally with one another at the base 
of the pollen-chamber. The common tube thus formed almost at once 
becomes coalescent with the nucellus, and the two run in continuity to the 
base of the seed. The free arms, however, so far maintain their indi- 
viduality as to be represented by very distinct ribs traversing the seed in 
the longitudinal direction. The grooves between the ribs are at first deep, 
but become shallower as the seed-base is approached — probably dying out 
at the insertion where the seed tapers to a blunt point (cf. PL V, Figs. 2 
and 1 ; PL VI, Fig. 13). The common, free tube of joined tentacles — the 
zone of the seed where there is a continuous free integument — is excessively 
short and practically negligible. It is only in the case of sections cut hori- 
zontally, or all but horizontally, that the existence of such a tube becomes 
apparent at all. Such a one is Dr. Scott’s section through a compressed 
seed (Scott Collection, 1907), which passes not quite horizontally through 
the region in question. At the top of the figure (PL VI, Fig. 15) — the actually 
highest part of the section— five arms are already entirely free, whilst at the 
bottom two are still confluent with each other and with the nucellus. On 
either side, however, are seen two pairs of tentacles still in tangential 
continuity, though free from the body of the seed, from which they are 
separated by a sinus (PL VI, Fig. 15, sn.). The figure shows the sinus in 
open communication with the exterior between the free tentacles. 
Another section from a slightly lower plane is shown in PL VI, Fig. 13. 
At the top of the figure (sn.) the beginnings of the sinus are apparent. The 
extreme vertical depth of the sinus is found by reference to PL VI, Fig. 18. 
