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 



Fig. 2. Coht'sion of two branches in Dipsaeus sylvestns. 



facilities for their union. An illustration of it is afforded 

 by the figure (fig. 2), showing cohesion affecting the 

 branches of a teazle {Di])sacm 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 



