52 SEED. 



is seen at (a) the mark on the face of a Kidney-bean ; 

 in most cases, it is of a darker colour than the 



Fig. 46. rest of the seed, as in the common Broad- 

 bean and Horse- chesnut. In small seeds it is 

 so minute as to be scarcely discernible. The 

 a apex of the seed is not always opposite the 

 base or hilum, but is sometimes even brought 

 down on a level with it ; it may often be de- 

 termined by observing the point at which cer- 

 tain radiating lines, seen upon the surface of 



many seeds, and having their base at the hilum, meet 



together ; or in other cases by the mark of the chalaza. 



287. The seed may be divided into three portions : 

 the coats, albumen, and embryo. 



288. The coats or integuments of the seed, spoken of 

 collectively, are termed the testa, which in many cases 

 can be separated into three distinct layers : the outer or 

 true testa, the second or sarcodermis, and the third or 

 endopleura. Sometimes, however, not more than one 

 distinct layer can be demonstrated, whilst it is stated 

 that in some examples five may be seen. The outer 

 integument is very various in nature and appearance, 

 from being fleshy to bony, and from smooth to hairy, 

 and often presents in its minute structure a peculiar 

 modification of fibre, or fibro-cellular tissue. 



289. Besides these proper seminal integuments, there 

 often exists another more or less partial one denomi- 

 nated the arillus ; this is seen in the 



Fig. 47. form of a membranous expansion of 



greater or less size, and variety of 

 figure, arising from the placenta along 

 with the funiculus, and extending it- 

 self over the body of the seed ; it 

 having been looked upon as charac- 

 teristic of this covering, that it is 

 never developed till after the fertilization of the ovule, 

 it has been considered quite distinct from the other co- 

 verings of the nucleus, and not to be considered in re- 

 lationship with them. But, as a German physiologist 



