408 



MR. MAIN'S VEGETABLE PHYSIOLOGY. 



law of vegetable nature ; for where do we find the most insignificant vegetable 

 body come into visible existence without having a pre-existing embryo or rudi- 

 mental atom, whence it derives its essential structure and qualities. There is no 

 such instance in nature. Can the most minute species of Fungi spring forth with- 

 out its propago, or the smallest herb without a seed, or previously existing part of 

 itself? Is the bark or wood self-productive ? No : when either is destroyed it 

 cannot be renewed but by the assistance of that vital member which is the origin 

 of both. 



" Admitting, then, that plants and certain parts of plants possess the property of 

 perpetual reproduction and extension, a question follows : How is this subdivision 

 effected ? In the case of bulbs it has already been stated that the radicle plate is 

 composed of an endless train of gems, which are developed in the order of their 

 seniority; tubers are multiplied by 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 appear as represented. 



Transverse and perpendicular sections of a stem four years old ; the latter through the pith, 

 a, pith and wood of the first year ; b, c,d, layers of wood of the second, third, and fourth 

 years j e, the four thin layers of bark. 



" 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 thus. 



Sections of a stem as it appears in May or June of the fifth year. The white spaces show 

 the swelling: cambium. 



