220 
ORGANOGRAPHY. 
BOOK I. 
seed becoming ripe the external integument is gradually ab- 
sorbed, until nothing but a thin membrane is left, usually 
described as epidermis testae, or in the Euphorbiaceae it has 
been given as arillus ; and, on the other hand, the actual 
modified epidermis testae has also been described as the 
arillus, for instance, in the Oxalideae. The apex of the 
original papilla, which developes itself as nucleus, varies ex- 
ceedingly in its size in proportion to the entire ovule, if 
examined in the different families. It often forms a long and 
nearly cylindrical body, as in Loasa and Pedicularis ; in many 
cases it is shorter, so that that portion of the ovule in which 
no distinction has taken place between nucleus and integu- 
ment (the whole being like a fleshy distended stalk) is by 
far the more predominant, as in all the Synanthereae, Canna, 
Phlox, Polemonium : it consists, again, in some instances 
merely of the extreme point of the papilla itself, as in Con- 
volvulus; or nothing more than an ideal point remains, which 
can no longer be distinguished as an independent body, 
above which, however, a protuberance developes itself, and 
thus forms a micropyle, as in the Dipsaceae. Of course the 
process I have been describing becomes considerably modi- 
fied in individual points.” 
Although the structure of the ovule is in general such as is 
above described, yet there is an exception to it of a character 
too remarkable to be passed over in silence. According to 
Mr. Griffith, the ovulum of Santalum album consists of nothing 
more than a naked nucleus, from within the apex of which 
the sac of the amnios protrudes in the form of a long tubular 
process. The same excellent botanist states that Loranthus and 
Viscum have an equally simple ovulum, and he considers it 
probable that it will hereafter appear that the sac of the amnios 
is the only essential part of an ovule. [Linn. Trans, xviii. 77.) 
The fluid matter contained within the nucleus is called the 
liquor amnios, and is supposed to be what nourishes the 
embryo during its growth. 
When an ovule grows erect from the base of the ovary, it 
is called erect ; when from a little above the base, ascending ; 
when it hangs from the summit of the cavity, it is pendulous ; 
and when from a little below the summit, it is suspended. 
