TEGMEN OR ENDOPLEURA.—ARILLUS. 337 
of the seed is smooth, and no evidence is afforded externally of 
its position. 
The testa is also usually marked externally by a scar indi- 
eating the hilum or point by which it is attached to the funi- 
culus or placenta. The micropyle, as already noticed (page 333), 
may be also sometimes seen on the surface of the testa, as in the 
Pea (jig. 748, m) ; but in those cases where no micropyle can be 
detected externally, its position can only be ascertained by dissec- 
tion, when it will be indicated by the termination of the radicle ; 
this being directed, as already alluded to (page 333), towards the 
micropyle. In some seeds, as in the Asparagus, the situation of 
the micropyle is marked by a small hardened point, which sepa- 
rates like a little lid at the period of germination: this has been 
termed the embryotegia. 
On removing the testa, we observe the raphe, which fre- 
quently ramifies over the inner coat, and where it terminates it 
constitutes the chalaza (fig. 757, ch, and 774, ch). The structure 
and general appearances of these different parts have been already 
described. (See page 333.) 
b. Tegmen, Endopleura, or Internal Coat (fia. 748, e).—The 
inner membrane or coat of the seed is essentially parenchy- 
matous like the outer. This integument usually appears to 
originate either from the substance of the nucellus or from 
the secundine of the ovule ; but sometimes in other ways. In 
many cases, however, it seems to be altogether wanting, which 
probably arises from its complete incorporation or adherence 
to the testa. Sometimes the embryo-sac in the ripe seed 
remains distinct from the albumen of the nucleus (fig. 762), 
and remains in the form of a bag or sac which envelopes 
the embryo, as in the Nymphzeaceze, Piperaceze, and Zingi- 
beraceze. To this distinct membrane the name of vitellus has 
been given. 
When clearly distinguishable the tegmen is generally of a 
soft and delicate nature, although sometimes it is of a fleshy 
character either entirely or in part. It is usvally of a whitish 
colour, and more or less transparent. This layer is closely ap- 
plied to the nucleus of the seed, which it accompanies in all its 
foldings and windings ; and in some cases even dips down into 
the albumen of the nucleus, and thus divides it more or less 
completely into a number of parts, as in the Nutmeg and Betel- 
nut (fig. 763, p). (See ALBUMEN, page 341.) The testa may 
either accompany the tegmen in its windings ; or, as more fre- 
quently happens, especially when the nucleus is curved, the tegmen 
alone follows the windings of the nucleus, the testa remaining in 
an almost even condition. 
Arillus.—Besides the two integuments described above as 
those that are usually found in all seeds, we occasionally find 
on the surface of some seeds an additional integument, which is 
generally of a partial nature (fig. 757, a, A), and to which the 
Z 
