644 



FARM ' SEEDS ' : SPECIAL 



red clover and kidney vetch; others are peculiarly marked 

 with streaks, dots, and marbled lines as in lupins, partridge 

 peas, and scarlet runner beans. The structure of the testa 

 is much the same in the whole Order, that of the pea is 

 given in cross section in Fig. 194. 



The outermost layer {a) consists of epidermal cells which 

 are thick-walled and largest in the direction of the radius of 



the seed. In consequence of the 

 hardness and shape of the cells 

 composing it, this is known as 

 the hard or palisade layer. The 

 cells generally contain colouring 

 matter, and cross their walls, 

 running parallel with the outside 

 of the seed, are one or more 

 lines where the light is strongly 

 refracted. Beneath the palisade 

 layer is another, {b) consisting of 

 smaller cells shaped like an hour- 

 FiG. 194,-Traiisverse section of the Mass. These layers (a) and lb) 



seed -coat of a pea. R j \ / \ r 



a Palisade - like layer of epidermal are met with in practically all 



cells ; b hour-glass-shaped cells ; z inter- J^ •' 



cellular space ; / thin-walled parenchy- seeds of the I-.egUminOSae. 

 matous cells which swell up when the 



seeds are soaked in water. (Enlarged Immediately beloW are tWO Or 



170 diameters.) , . . _ 



more layers consisting of paren- 

 chymatous cells, the longest diameter of which is parallel to 

 the surface of the seed. When dry they are more or less 

 pressed together, but on soaking in water they swell to a 

 considerable size. 



If a number of seeds of red clover are placed in water for 

 a few hours, it will usually be found that some of them, 

 instead of absorbing water and swelling considerably like the 

 rest, remain the same size and shape as they were when put 

 in. These are called 'hard seeds,' and the peculiar resist- 



