218 
ORGANOGRAPHY. 
BOOK I. 
Urtica, and others, where it is said to be antitropal. But if 
the ovule undergoes the remarkable extension of one side 
already described in speaking of that organ, when the sacs 
are so inverted that their orifice is next the hilum, and their 
base at the apex of the ovule, then there will be a raphe 
and chalaza distinctly present; and the radicle will, in the seed, 
be at the end next the hilum, and the embryo will be erect 
with respect to the seed, or orthotropal^ as in the apple, 
plum, &c. On the other hand, supposing that the sacs of 
the embryo suffer only a partial degree of inversion, so that 
their foramen is neither at the one extremity nor the other, 
there will be a chalaza and a short raphe ; and the radicle will 
point neither to the apex nor to the base of the seed, but the 
embryo will lie, as it were, across it, or be heterotrvpal^ as is 
the case in the primrose. When an embryo is so curved as 
to have both apex and radicle presented to the hilum, as in 
Reseda, it is amphitropaL 
In the words of Gaertner, an embryo is as^cending when its 
apex is pointed to the apex of the fruit ; descending^ if to the 
base of the fruit; centripetal^ if turned towards the axis of 
the fruit ; and centrifugal, if towards the sides of the fruit : 
those embryos are called wandering, or vagi^ which have no 
evident direction. 
The cotyledons are generally straight, and placed face to 
face ; but there are numberless exceptions to this. Some are 
separated by the intervention of albumen (Plate VI. fig. 11.) ; 
others are naturally distant from each other without any 
intervening substance. Some are straight, some waved, 
others arcuate or spiral. When they are folded with their 
back upon the radicle, they are called incumbent ; if their 
edges are presented to the same part, they are accumhent ; 
terms chiefly used in speaking of Cruciferae. 
15. Of Naked Seeds. 
By naked seeds has been understood, by the school of Lin- 
naeus, small seed-like fruit, like that of Labiatae, Boraginea?, 
grasses, and Cyperaceae. But as these are distinctly covered 
