'226 PROCESS OF DEVELOPEMENT. CHAP. IV. 



This is much more likely to be the case than that 

 the alburnum should extend itself laterally, which 

 is contrary to the experiments of Du Hamel, and 

 also to the scope of Mr. Knight's general con- 

 clusion ; namely, that the sap after being exposed 

 to the action of the light in the leaves, and con- 

 verted into proper juice, is again carried back by 

 the returning vessels of the leaf and leaf-stalk to 

 the bark, by which it is conveyed throughout the 

 whole extent of the plant, to add new matter and 

 to compose the different organs for the succeeding 

 year.* 



Augment- Such then is the mode of the augmentation of 

 succeeding the plant in the second year of its growth. It ex- 

 tends in width by a new layer of wood and of 

 bark insinuated between the wood and bark of the 

 former year ; and in height by the addition of a 

 perpendicular shoot or of branches, generated as 

 in the shoot of the first year. But if the plant is 

 taken and dissected at the end of the third year, it 

 will be found to have augmented in the same 

 manner ; and so also at the end of the succeeding 

 year as long as it shall continue to live ; so that the 

 outermost layer of bark, and innermost layer of 

 wood, must have been originally tangent in the first 

 year of the plant's growth ; the second layer of 

 bark, and second layer of wood, in the second 

 year ; and so on in the order of succession till you 

 come to the layer of the present year, which will 



* Phil. Trans. 1805. 



