12 INTRODUCTION. 



by the growth of the internodial parts. Accord- 

 ing to the strength or age of the plant, a greater 

 or lesser number of flower-stems rise, blow^, and 

 die. The rest remain till the next or following 

 years ; and of these layers, cuttings, or pipings, 

 are made for the purpose of propagation. 



All roots, whether designated fibrous, bulbous, 

 or tuberous, put forth thread-like fibres, which are 

 the chief agents for collecting the nutritious 

 qualities from the earth for the use of the plants. 

 They are of very curious and delicate structure, 

 impatient of dry air, or of any change of tem- 

 perature or humidity. Their growth is always 

 cotemporary with the other motions of the plant, 

 and, indeed, the ascending and descending ex- 

 pansion of vegetable life seem to receive counter 

 impulses from each other. Fibres cannot be 

 produced, it appears, without some internal force 

 or excitement ; so neither can any material ex- 

 pansion talvc place in the air but by their as- 

 sistance. The tender shoots and some of the 

 fibres of shrubs and trees become woody in time ; 

 but, in most kinds of bed and border flowers, 



