PHENOMENA OF PLANT-LIFE. 39 



atmosphere still retains life, are questions which have not 

 beeii definitively answered. It v is not easy to say wherein the 

 vitality of any perfectly formed tissue, whether of the wood 

 or bark, consists, since their cells have no power of enlarge- 

 ment or multiplication, though the thickening of the cell-walls 

 by the deposition of substances within the cells and the strik- 

 ing changes in color, seem to indicate the presence of a feeble 

 life. The functions of the wood seem to be mainly such as 

 may be performed by dead material. The cellulose which has 

 never been exposed to the air may retain its peculiar affinity 

 for water, which is evidently much greater before than after 

 drying. The cells may serve as reservoirs of starch and 

 other substances which may afterwards be imbibed by the 

 living, growing or ripening tissues. The pith, which is alive 

 in young branches so long as leaves are borne upon their 

 wood, dies apparently with them. If growth is a characteristic 

 feature of living tissue, our trees may with some reason be 

 considered annuals, since all their growth proceeds normally 

 from their winter buds and completely envelops every portion 

 of the tissues of the roots, stems and branches previously 

 formed, thus excluding them from the weather and pre- 

 venting their decay, while using them for a support and 

 a magazine of supplies. However this may be, it is cer- 

 tain that the vitality of trees is concentrated in a remarkable 

 manner upon the surface and the extremities of their roots 

 and branches. 



Among the observations made during the past season, not 

 the least interesting were those relating to the natural graft- 

 ing which is frequently to be seen in the forests, and which is 

 particularly noticeable among roots. The almost incredible 

 manner in which the living surface of the inner bark of woody 

 stems can transform the same elaborated sap into different 

 species of wood and bark, was alluded to last year, and the 

 case mentioned of a possible compound tree, containing a 

 plum root and base, on which grew a stem of apricot, sur- 

 mounted by a stem of blood peach with red wood, and that 

 by a stem of Avhite peach, and the whole by a stem and 

 branches of almond. Thus, each kind of wood and bark 

 would be perfectly developed from the same material, just as 

 on the same cow's milk may be fed a child, a calf, a colt, a 



