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 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 geometi'ical 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. Where 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. Z>, &c.) ; 

 and a substance interposed between the embryo and the 

 testa, the albumen (fig. 1. a, 5. «, &c.). 



The testa, called also lorica by IVIirbel, perisperme and 

 cpisperme by Richard, and spermodermis by De Candolie 

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



s; 



