146 DEVELOPMENT OF THE OVULUM 
quent paragraph which I have quoted before. The real con- 
struction is obviously this—that the amnios exists in all 
plants in its earlier stages, in a few only in its more mature 
stages. 
Outer integument, Testa, Primine of Mirbel. 
This coat, the outermost in the unimpregnated ovulum, 
continues the most external covering of the organ as it 
advances to maturity, except in some instances of unusual 
development of the arillus. Great changes however may 
occur in it, so that its original state shall, in the ripe 
seed, be totally obscured. 'This was pointed out by M. 
Mirbel. 
The presence of vessels will, in all doubtful cases, decide 
whether the tegument is testa or tegmen. For this we are 
indebted to Mr. Brown, whose remarks I cannot refrain from 
quoting —“ The testa, or outer coat of the seed, is very ge- 
nerally formed by the outer membrane of the ovulum ; and 
in most cases where the nucleus is inverted, which is the 
more usual structure, its origin may be satisfactorily de- 
termined ; either by the hilum being more or less lateral, or 
more obviously and with greater certainty, where the raphe 
is visible, this vascular cord uniformly belonging to the out- 
er membrane of the ovulum. 
“The chalaza, as properly so called, though perels 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 acquainted with any character by which it can 
be absolutely distinguished from the inner membrane in the 
ripe seed; but as few plants are already known, in which 
the outer membrane is originally incomplete, its entire 
absence, even before fecundation, is conceivable: and some 
