IN FLOWERING PLANTS. 147 
possible cases of such a structure will be mentioned here- 
after." 
In many instances, however, in which the vascular system 
is totally wanting, no proof can be given of the true na- 
ture of the tegument. Because such want of vascularity is 
by no means confined to any modification of an ovulum, of 
this there are obvious instances. 
And again, with regard to those cases in which singleness 
of covering results from adhesion, it is in many cases difficult 
and perhaps impossible to distinguish the limits of the coats, 
while in others, although the union be firm, lines ane 
the original distinction are visible enough. 
In all such cases recourse must be had to examination at 
a sufficiently early period, on this Mirbel very justly lays 
great stress, and he has given it'as his opinion, that in 
almost all cases, and perhaps in all, two teguments really 
exist at some period or another. 
Arilius, . 
This production remains to be explained. This name has 
been applied to every substance mereala the seed of an 
unusual nature. . 
Thus the testa of Cucurbitacez is "uid else but the 
separation of that part of the fruit lining each cavity in which 
the seed is lodged. In other plants, as in Ternstreemiacee, 
etc. it is a growth of the testa. 
The true Arillus is a mere growth of the funicle, as Mr. 
Brown has remarked ; it is never complete, and its develop- 
ment takes place chiefly after fecundation. ‘“ It is, however, 
worthy of remark, that in the early stage of the ovulum, this 
envelope is in general hardly visible even in those cases, 
where, as in Hibbertia volubilis, it attains the greatest size 
in the ripe seed; nor does it in any case, with which I am ` 
acquainted, cover the foramen of the testa until after fecunda- 
tion,” it varies much in form, but in general bas more or less 
of a cup shape; in others as in Pharnaceum, it is filiform. 
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