GROWTH OF TREES. 143 



and tubes of the woody layer of the preceding year, as 

 well as the new inner layer of the bark. Hales like- 

 wise says that he agrees in opinion with Borelli, who 

 supposes the tender growing shoot to be distended like 

 soft wax, by the expansion of the moisture of the 

 spongy pith. 



M. Mustel says, that emanations from the ligneous 

 body form a new layer of wood, by means of the rising 

 sap, and that emanations from the inner bark form, at 

 the same time, a new layer of inner bark by means of 

 the descending sap, by which latter term he must mean 

 pulp. 



Du Hamel, in order to satisfy himself respecting the 

 truth of Grew's opinion, introduced a plate of metal 

 between the bark and the wood of a tree early in spring, 

 and when this was examined two or three years after- 

 wards, it was found embedded in the wood, proving 

 that the bark was not produced by the wood, though 

 it was hence clear that the wood was formed on the 

 outside of the metal plate. He came to the conclusion 

 that the inner bark is every year changed into pulp- 

 wood, and a new layer of inner bark formed to replace 

 this. In the seed, before germination, he says, there 

 is nothing but a dense tissue of cells, and no vessel can 

 be traced : yet soon after the beginning of germination, 

 a ring of vessels appears to form the commencement of 

 the pith- tube, having the pith within it still green, and 

 full of a watery fluid. Soon after, there appears out- 

 side the pith-tube, a layer of pulp which goes to form 

 the first portion of the inner and outer bark, and as 

 soon as there is another layer of pulp to replace this, 



