26 HILUM APEX TESTA. [BOOK i. 



understood. The base of a seed is always that point by which 

 it is attached to the placenta, and which receives the name 

 of hilum ; the base being found, it would seem easy to deter- 

 mine the apex, as a line raised perpendicularly upon the 

 hilum, cutting the axis of the seed, ought to indicate the apex 

 at the point where the line passes through the seed-coat ; but 

 the apex so indicated would be the geometrical, not the natural 

 apex : for discovering which with precision in seeds, the 

 natural and geometrical apex of which do not correspond, 

 another plan must be followed. If the skin of a seed be 

 carefully examined, it will usually be found that it is com- 

 posed in great part of lines representing rows of cellular 

 tissue, radiating from some one point towards the base, or, 

 in other words, of lines running upwards from the hilum and 

 meeting in some common point. This point of union or 

 radiation is the true apex, which is not only often far removed 

 from the geometrical apex, but is sometimes even in juxta- 

 position with the hilum, as in mignionette : in proportion, 

 therefore, to the obliquity of the apex of the seed will be the 

 curve of its axis, which is represented by a line passing 

 through the whole mass of the seed from the base to the apex, 

 accurately following its curve. If the lines above referred to 

 are not easily distinguished, another indication of the apex 

 sometimes resides in a little brown spot or areola, hereafter 

 to be mentioned under the name of chalaza. 



The integuments of a seed are called the testa ; the rudi- 

 ment of a future plant the embryo (Plate VI. fig. 1. b, &c.) ; 

 and a substance interposed between the embryo and the testa, 

 the albumen (fig. 1. , 5. , &c.) 



The testa, called also lorica by Mirbel, perisperm and 

 episperm by Richard, and spermoderm by De Candolle, consists, 

 according to some, like the pericarp, of three portions ; 

 viz., 1. the external integument, tunica externa of Willdenow, 

 testa of De Candolle ; 2. the internal integument, tunica 

 interna of Willdenow, endopleura of De Candolle, hilofere and 

 legmen of Mirbel; and 3., of an intervening substance an- 

 swering to the sarcocarp, and called sarcoderm by De Can- 

 dolle : this last is chiefly present in seeds with a succulent 



