460 THE SEED AND ITS GEUMIXATION. 



1192. Ripening of frnits and seeds. The structural changes 

 attending this process, taken together, result in adaptations for 

 providing the embryo with an ample supply of food, for giving it 

 adequate protection during its resting state, and for securing 

 its dissemination. 



1193. The chemical changes comprise chiefly the storing up 

 of a sufficiency of food of a proper character to support the 

 embryo for a time. In pulpy fruits they are mostly associated 

 with the consumption of a certain amount of oxygen and the 

 liberation of more or less carbonic acid. Many of the chemical 

 changes can go on after the separation of the fruit or seed from 

 the parent plant. 



In the ripening of pulp3- fruits the important changes in 

 texture are attended by the formation of sugars, acids, etc., and 

 by modifications in the character of the walls of cells. 



1194. Dissemination is most frequently secured by (1) some 

 meclianism for transport by air, water, fleece, or plumage ; (2) 

 the construction of some expulsive apparatus ; (3j the existence 

 of certain attractions of taste, color, and odor, by which the 

 seeds are made the food of birds. In the last case the germ 

 itself, protected against the action of digestive juices, is often 

 carried to great distances from the parent plant. 



1195. Ripeness of seeds. The embryo is sometimes viable, or 

 capable of independent life, at a very earl^' stage. Immature 

 seeds are of course deficient in tiieir suppl}- of proper food for 

 the embryo, which is onl3- imperfectly developed, and their in- 

 teguments are not yet adapted to protect the germ adequately. 

 But in certain instances such seeds ma^- germinate, giving rise 

 to strong and healthy plants. Cohn ' has shown that seeds which 

 are not perfectly ripe germinate somewhat sooner tiian tiiose 

 which are more mature ; this moans that the store of food is in 

 a condition which admits of immediate use. He has further 

 pointed out that seeds separated from the plant, but still enclosed 

 in the pericarp, ripen ; and he believes that those seeds which 

 have reached a medium stage of ripeness germinate most readily. 

 " Viability does not coincide with ripeness ; it precedes it." ^ 



1196. Shortly before the period of ripening, the part which 



1 Flora, 1849, p. 481. 



2 There is some reason to believe that in the case of certain cultivated vege- 

 tables unripe seeds may give rise to earlier varieties than come from ripe seeds. 

 For numerous citations from the extensive literature of the subject see a paper 

 by the author in the Report of the Secretary of the Massachusetts Board of 

 Agriculture for 1878. 



