LECT. VIII.] ORIGIN OF BRANCHES. 389 



with the new layer in the stem, deposited over 

 that of the former year, which has already be- 

 come wood : and, as the branch increases an- 

 nually by new layers, in the same manner as the 

 stem, a similar section made at any subsequent 

 period displays its connexion with the stem, form- 

 ing a cone, the apex of which touches the me- 

 dullary sheath of the stem, and the base its sur- 

 face whence the branch projects. This conical 

 appearance is rendered more 

 evident by the marginal cut; 

 in which a. represents a stem 

 five years old ; and b. a branch 

 three years old projecting from 

 it. At the points of union 

 (c. c.) a kind of raphe is formed 

 above and below the branch 

 owing to the descending albur- 

 nous matter of the branch 

 meeting that of the stem. 



Such are the appearances which mark the 

 origin of the branch and its connexion with the 

 trunk in the Lilac ; and the same, with some 

 modifications, are perceptible in all ligneous dico- 

 tyledons. The principal of these modifications is 

 seen in those ligneous stems, the pith of which is 

 interrupted at the points where the buds are 

 formed, as for example in that of the Vine. In it 

 a process from the medullary sheath extending di- 



c c 3 



