xvn MORPHOLOGY OF SEEDS AND FRUIT 235 



EXPT. 201. Place some seeds of the Pumpkin on damp sawdust, 

 and examine them from time to time. Note 



(i) The seed is flattened, oval in outline, and possesses a thickened 

 border. At one end the hilum and micropyle occur. Split open the 

 cotyledons ; observe it is an exalbuminous seed. 



(ii) The young radicle (when it appears through the micropyle) grows 

 downwards and fixes itself in the soil. 



(iii) The young radicle possesses a peg or projection on the lower 

 side which pins down the seed-coats while the cotyledons are extracted. 



(iv) The hypocotyledonous portion, when it comes out of the seed, is 

 arched ; this enables it to lift the soil far better than if it came up 

 straight. 



(v) The cotyledons increase in size, open out, and perform the work 

 of assimilation. 



EXPT. 202. Compare plants in various stages of germination. 

 Note 



(i) The embryo swells and bursts the testa. 



(ii) The radicle comes out of the micropyle and curves downwards and 

 enters the soil. 



(iii) The hypocotyledonous stem, or portion beneath the cotyledons, 

 comes up curved. 



(iv) The cotyledons are green even beneath the ground. They 

 elongate and spread when exposed to light. 



(v) The plumule develops and produces the foliage leaves. 



SUMMARY 



Changes in the Embryo-sac form the endosperm, and convert the 

 ovule into a seed. Seeds may be albuminous, i.e., have endosperm and 

 embryo in the embryo-sac ; or exalbiuninous, i.e., have only the embryo 

 in the embryo-sac. 



The Seed is covered with a testa which encloses the embryo and also 

 the endosperm if it is present. 



The Aril is a growth formed from some part of the ovule. 



Fruits are divided into true fruits and spurious fruits. A true 

 fruit is formed from a single gyncecium. In a spurious fruit some 

 other portion of the flower takes part in its formation. The wall of 

 fruits is called the pericarp, which can be divided into epicarp, meso- 

 carp, and endocarp. Fruits may either dehisce or open to liberate the 

 seeds, or they may not dehisce. 



True fruits may be succulent or dry, and can be arranged into 



Succulent. Dry. 



The drunlets The achene - The legume. 



The schizocarp. The follicle. 



The capsule. 



