218 ORGANOGRAPHY. BOOK I. 



Urtica, and otliers, 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 lieterotropal, 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 ascending 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 vaxji, 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 accumbent ; 

 terms chiefly used in speaking of Cruciferoe. 



15. Of Naked Seeds. 



By naked seeds has been understood, by the school of Lin- 

 naeus, small seed-like fruit, like that of Labiatas, Boragineae, 

 grasses, and Cyperaceae. But as these are distinctly covered 



