784 PHYSIOLOGY. 



part in the changes which are taking place during the ripening 

 of the fruit. M. Fremy has discovered a new acid in fruits, to 

 which he has given the name of cellulic acid ; but at present 

 nothing is known of its action or use in the plant. 



Bijpening of Fruits. — The time when a fruit is considered 

 ripe varies in different cases. When the pericarp is of a dry 

 nature, the fruit is looked upon as ripe just before it opens ; but 

 when the pericarp is of a pulpy nature and edible, we com- 

 monly regard it as mature when most agreeable as food. Hence 

 the Apple is considered to be ripe in a state in which the Medlar 

 would be regarded as unripe. 



When succulent fruits are ripe, they undergo another change, 

 a species of oxidation, which produces a decay, or bletting of 

 their tissues, as it has been called by Lindley. This bletting, 

 according to Berard, is especially evident in the fruits of the 

 Pomacese and Ebenacese, and it would appear that the more 

 austere the fruit is, the more it is capable of bletting regu- 

 larly. Bletting appears to be peculiar to such fruits, and may 

 be regarded as a state intermediate between maturity and decay. 

 A Jargonelle Pear, in passing from ripeness to bletting, accord- 

 ing to Berard, loses a great deal of water (83-88, which it 

 contains when ripe, being reduced to 62-73) ; much sugar (11-52, 

 being reduced to 8-77); and a little lignin (2-19, reduced to 

 1-85) ; but it acquires, at the same time, rather more malic acid, 

 gum, and animal matter. 



The time required by different plants for ripening their fruits 

 varies much, but almost all fruits come to maturity in a few 

 months. Some, as those of Grasses generally, require but a few 

 days ; while others, as some of the Coniferse, &c., more than 

 twelve months. 



4. Of the Seed, — The structure and general characters of 

 the seed, as well as the origin and progressive development of 

 its parts, have been already fully alluded to in a former section 

 of this work (pp. 326—343). 



Our limited space prevents us from alluding to the multitude 

 of ways and contrivances by which the natural dissemination of 

 seeds is eflfected ; and to the number of seeds produced by plants. 

 Sufl&ce it to say that, in all cases, a great many more seeds are 

 matured than are required for the propagation of the species ; 

 and thus the extinction of the species in consequence of their 

 decay, their use for food by animals, &c., is provided against. 



Vitality of Seeds. — Seeds vary very much as to the time during 

 which they will preserve their power of germinating. This vita- 

 lity is frequently lost long before they lose their value for food. 

 Some seeds of an oily or mucilaginous nature, or which contain 

 much tannic acid, speedily lose their vitality, and decay ; this is 

 the case, for instance, with Nuts and Acorns, and hence, when 

 seeds of this nature are required for propagation, they must be 



