140 



SEAT OF VEGETABLE LIFE. 



division or branches ; fibrous-rooted herbaceous plants 

 perpetuate themselves by lateral offsets ; but how is 

 the annual subdivision of the vital envelope of trees 

 accomplished ? To this question a direct answer 

 cannot be given, because the process is invisible ; 

 but we can gain a knowledge of the changes which 

 take place between the wood and the liber of a tree 

 by making frequent incisions through the bark, and 

 marking the changes during the spring, summer, and 

 autumn growth. 



In early spring, say in the beginning of February, 

 the transverse and vertical sections of the stem of 

 four years old appears as represented. (Fig. 43.) 



Fig. 43. 



Transverse and perpendicular sections of a stem four years old ; 

 the latter through the pith, a, pith and wood of the first year ; 6, 

 c, d, layers of wood of the second, third, and fourth years ; e, the 

 four thin layers of hark. 



About the end of May, sooner or later, according 

 to the favourableness of the season, similar sections 

 of a stem of the same age will appear as Fig. 44, 



