VITALITY OF SEEDS. 103 



or dissipate this constituent; and, on the other hand, an 

 excessive supply of water vdll retard or prevent ripening, in 

 consequence of the longer time required for the same purpose. 



Seeds are affected hy all circumstances that affect the fruit, 

 which, indeed, as has heen already stated, appears to he 

 created for their nutrition and preservation. In general, the 

 fruit attracts organizahle matter from the stem through the 

 stalk, and the seed from the fruit through its placenta ; * and 

 this accounts, independently of other causes, for the importance 

 of the fruit to the seed. 



When the seed is ripe it is dry, all its free water being 

 parted with ; and its interior is occupied by starch or fixed oil, 

 or some other such substance, together with earthy matters. It 

 would seem that, so long as these secretions remain un- 

 decomposed, so long does the vitahty of the seed continue 

 unimpaired ; and hence the great age at which certain kinds of 

 seeds have been found to grow. But, as it is difficult to 

 prevent their decomposition, so is it difficult to preserve 

 seminal vitality for any considerable time ; and the differences 

 found in the duration of the growing powers of seeds probably 

 depend principally upon differences in their chemical consti- 

 tution. Oily seeds, which readily decompose, are among the 

 most perishable; starchy seeds, which are least subject to 

 change, are the most tenacious of life. 



Not to speak of the doubtful instances of seeds taken from the 

 Pyramids having germinated, Melons have heen known to grow at the 

 age of forty years, Kidneybeans at a hundred, Sensitive-Plant at sixty. 

 Rye at forty; and there are now living, in the garden of the 

 Horticultural Society, Easpberry plants raised from seeds sixteen- 

 hundred or seventeen-hundred years old. The seeds of Charlock 

 buried in former ages spring up in railway cuttings ; where ancient 

 forests are destroyed, plants appear which had never been seen before, 

 but whose seeds have been buried in the ground ; when some land was 

 recovered from the Baltic sea, a Carex was found upon it, now unknown 

 in that part of Europe. M. Fries, of Upsala, succeeded in growing a 



* The placenta is a soft part of the interior of a fruit, upon wMch the seed ia 

 formed. It is composed of tMn-sided parenchyma, the most absorbent of all the 

 forms of tissue, and is in oommunication, by its whole surface, -with the parenchyma 

 of the firuit. 



