246 
ORGANOGRAPHY. 
BOOK I. 
“ This third coat (tercine) is formed by the proper mem- 
brane or cuticle of the nucleus, from whose substance in the 
unimpregnated ovule it is never, I believe, separable, and at 
that period is very rarely visible. In the ripe seed it is dis- 
tinguishable from the inner membrane only by its apex, 
which is never perforated, is generally acute and more deeply 
coloured, or even sphacelated.” 
Mirbel has, however, j ustly remarked that the primine and 
the secundine are, in the seed, very frequently confounded ; 
and that, therefore, the word testa is better employed, as one 
which expresses the outer integument of the seed without 
reference to its exact origin, which is practically of little im- 
portance. The tercine is also, no doubt, often absent. He 
observes that these mixed integuments often give rise to new 
kinds of tissue ; that in Phaseolus vulgaris the testa consists, 
indeed, of three distinct layers, but of those the innermost 
was the primine ; and that the others, which represent nothing 
that pre-existed in the ovule, have a horny consistence, and 
are formed of cylindrical cellules, which elongate in the direc- 
tion from the centre to the circumference. And this is pro- 
bably the structure of the testa of many Leguminosae. 
It sometimes happens that the endopleura (or tercine?) 
thickens so much as to have the appearance of albumen, as 
in Cathartocarpus fistula. In such a case it is only to be 
distinguished from albumen by gradual observation from the 
ovule to the ripe seed. 
One of the innermost integuments is occasionally present 
in the form of a fleshy sac, interposed between the albumen 
and the ovule, and enveloping the latter. It is what was 
called the vitellus by Gaertner, and what Richard, by a 
singular prejudice, considered a dilatation of the radicle of 
the embryo : to his macropodal form of which he referred the 
embryo of such plants. Instances of this are found in Nym- 
phaea and its allies, and also in Zingiberaceae, Peppers, and 
Saururus. Brown, who first ascertained the fact, considers 
this sac to be always of the same nature and origin, and as 
the vesicula colliquamenti or amnios of Malpighi. 
The end by which the seed is attached to the placenta is 
called the liilum or umbilicus (Plate VI. fig. 5. c, 17. c, 11. c. 
