206 
ORGANOGRAPHY. 
BOOK I. 
When a seed is flattened lengthwise it is said to be com- 
pressed, when vertically it is depressed ; a difference which it 
is of importance to bear in mind, although it is not always 
easy to ascertain it: for this purpose it is indispensable that 
the true base and apex of the seed should be clearly under- 
stood. 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 w^hich with precision in seeds, the 
natural and geometrical apex of w^hich 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 
resides in a little brown spot or areola, hereafter to be men- 
tioned under the name of chalaza. Wliere there is no in- 
dication either externally or internally of the apex, it may 
then be determined geometrically. 
The integuments of a seed are called the testa; the rudi- 
ment of a future plant, the embryo (Plate VI. fig. 1. &c.) ; 
and a substance interposed between the embryo and the 
testa, the albumen (fig. 1. a, 5. «, &c.). 
The testa, called also lorica by Mirbel, perisperme and 
episperme by Richard, and spermodermis by De Candolle, 
according to some consists, like the pericarp, of three portions ; 
