Botany.] 
NATURAL HISTORY. 
551 
cases where the nucleus is inverted, which is the more usual 
structure, its origin may be satisfactorily determined ; either 
by the hilum being more or less lateral, while the foramen 
is terminal; or more obviously, and with greater certainty 
where, the raphe is visible, this vascular cord uniformly 
belonging to the outer membrane of the ovulum. The 
chalaza^ properly so called, though merely the termination 
of the raphe, affords a less certain character, for in many 
plants it is hardly visible on the inner surface of the testa, 
but is intimately united with the areola of insertion of the 
inner membrane or of the nucleus, to one or other of which 
it then seems entirely to belong. In those cases where the 
testa agrees in direction with the nucleus, I am not ac- 
quainted with any character by which it can be absolutely 
distinguished from the inner membrane in the ripe seed ; 
but as a few plants are already known, in which the outer 
membrane is originally incomplete, its entire absence, even 
before fecundation, is conceivable; and some possible cases 
of such a structure will be mentioned hereafter. 
There are several cases known, some of which I have for- 
merly noticed of the complete obliteration of the testa in 
the ripe seed ; and on the other hand it appears to consti- 
tute* the greater part of the substance of the bulb-like seeds 
of many Liliaceae, where it no doubt performs also the func- 
tion of albumen, from which, however, it is readily dis- 
tinguished by its vascularity t. But the most remarkable 
deviation from the usual structure and economy of the outer 
membrane of the ovulum, both in its earliest stage and in 
the ripe fruit, that I have yet met with, occurs in Banksia 
and Dr^andra. In these two genera I have ascertained that 
the inner membrane of the ovulum, before fecundation, is 
^ Linn, Soc. Transact, xii. p. 149. 
t Ibid. 
