10 COHESION. 
Thirdly. The branches become united to the stem; 
or, lastly, the roots may become fused one with 
another. 
The first of these is most commonly met with, 
doubtless owing to the number of the branches and the 

Fic. 2.—Cohesion of two branches in Dipsacus sylvestris. 
facilities for their union. An illustration of it is afforded 
by the figure (fig. 2), showing cohesion affecting the 
branches of ateazle (Dipsacus sylvestris). Union of the 
branches may be the result of an original cohesion of the 
buds, while in other cases the fusion does not take place 
until after development has proceeded to some extent. 
Of this latter kind illustrations are common where the 
branches are in close approximation ; if the bark be 
removed by friction the two surfaces are very likely to 
become united (natural grafting). Such a union of 
the branches is very common in the ivy, the elder, the 
beech, and other plants. It may take place in various 
