234 PHYSIOLOGICAL BOTANY. FART II. 



thorn is capable of sustaining a greater degree of cold 

 than it otherwise could. In some cases the crop of 

 fruit is increased, in others it is diminished ; and some 

 plants which are naturally climbers become more 

 bushy, &c. 



(230.) Development. The process of development 

 never appears to be entirely stationary in the living 

 plant, not even during winter when the repose of vege- 

 table life is the most marked ; but a slight progression 

 of the sap is still going on and a trifling enlargement of 

 the buds is gradually taking place. As the spring ad- 

 vances the vital energies revive and vegetation seems 

 to awaken ; a sudden and rapid flow of the sap towards 

 the extremities takes place, and the buds begin to de- 

 velop with great rapidity. It is evident that the in- 

 creased temperature of the atmosphere is a stimulating 

 cause in producing these effects ; and they may be par- 

 tially accelerated or retarded by artificial means. If 

 for instance a branch of any tree growing in the open 

 air is introduced into a hothouse during the winter, 

 the buds upon it swell and put forth leaves although 

 the rest of the tree continues bare. 



(231.) Vernal Development. The different degrees 

 of vigour with whicK buds burst forth in spring in 

 different years, is probably regulated by the quantity 

 of nutriment which has been prepared and laid up in 

 the stem during the previous summer ; so that a more 

 rapid development will take place after a fine season 

 than after a bad one. The extraordinary activity which 

 vegetation evinces in the spring, appears to depend upon 

 the great freshness of those parts by which the several 

 processes of nutrition are then conducted. New fibres 

 have been formed at the roots during the winter, and 

 their absorbing powers now act with the fullest energy ; 

 the young leaves have their vessels and vesicles quite 

 fresh, and unobstructed by the deposition of those 

 earthy matters which are afterwards found in them 

 when the exhalation of moisture from their surface 

 has been going on for some time. If a branch of the 



