REPRODUCTION OF PLANTS. 101 



standing so much apparent identity, between the 

 products of the two methods of reproduction 

 above mentioned. In the case of propagation by 

 seed, the embryo is really, and from the first 

 moment of its existence, a being distinct from 

 the parent plant, the seed is furnished with all 

 the organs it requires ; the tubercle, on the con- 

 trary, is but a fragment of the plant that bore it, 

 and has gradually to form for itself the needful 

 organs. The seed, being entirely distinct, may 

 only resemble the original plant by the general 

 characteristics that belong to its kind ; while the 

 tubercle or the cutting, being actually portions 

 of the plant itself, preserves its minutest particu- 

 larities. A very curious instance of reproduc- 

 tion occurs in the lemna, or common duckweed. 

 If one of its little discs be placed in a saucer, we 

 shall soon see it send forth laterally a tubercle 

 which grows in a horizontal direction, puts out 

 a root underneath, and thus forms a second 

 plant similar to the former, but united with it. 

 This double disc continues to vegetate in the 

 same manner, and so on. 



75. Besides the method of increase by cut- 

 tings, tubercles, &c. mentioned above, another 

 exists which is, as all gardeners well know, of 

 immense practical utility that of grafting, 



