CHAPTER X. 



SEEDS AND FRUITS. 



MORPHOLOGY. 



A seed or matured ovule belongs to one of two categories : (i.) 

 exalbuminous, (2.) albuminous, i.e., without and with albumen 

 respectively. 



A broad bean is a good example of the former sort. If pre- 

 viously soaked in water the examination will be facilitated. A 

 black mark will be seen at one end. This is the scar or hilum, 

 from which the stalk has been detached. As the ovule was 

 inverted (p. 104) the seed must be so. The micropyle should 

 therefore be close to the scar (fig. 49), and in squeezing the seed 

 a drop of water will ooze out, and prove its presence. A trian- 

 gular swelling on this side l the scar marks the position of the 

 radicle, which is in part (cf. p. 143) the primary root of the 

 embryo. A slight ridge, the rajme (p. 109), runs from the other 

 side of the scar half way along the seed to what correspond with 

 the base of the ovule, exactly opposite the micropyle. The long 

 axis of the seed is therefore the direction of breadth. A skin or 

 seed-coat can readily be peeled off, consisting of a thick outer and 

 a thin inner layer, developed respectively from outer and inner 

 integuments of the ovule. The greater part of the seed is made 

 up of two thickened fleshy cotyledons or seed-leaves, which are the 

 first leaves of the embryo (cf. figs. 2 and 5). Note also the white 

 pointed radicle. Now separate the seed-leaves, and observe that 

 the radicle is continuous with a minute curved plumule, or primary 

 shoot. The space within the seed-coats is entirely occupied by 

 the embryo, and all trace of the nucellus has disappeared. The 

 presence of two seed-leaves characterizes dicotyledons generally. 

 A dried pea, the kernels of almond and hazel-nut, ■ apple and 

 orange pips, can all be understood by comparison with bean. 



A large and typical albuminous seed is that of castor-oil, obtain- 

 able from any druggist. It is oval, flattened, and mottled. At 

 one end is a small knob, the caruncle, which marks the position 

 of both hilum and micropyle, for the seed is a reversed one. 



1 I.e., left when the bean is placed so that the scar is below and to right. 



132 



