COHESION. 9 



column of Orchids may be referred to as an illustration 

 under natural circumstances of the complete union of 

 many usually distinct parts. 



In the uncertainty that exists in many cases as to 

 the real nature of tlie occurrence, it would be idle to 

 attempt to explain the causes of fusions. It is clear, 

 however, that an arrest of development will tend 

 towards the maintenance of primordial integrity (con- 

 genital ftision), and that pressure will induce the 

 coalition of organs primarily distinct. 



CHAPTER I. 



COHESION. 



Following Augustin Pyramus De CandoUe, botanists 

 have applied the term cohesion to the coalescence of 

 parts of the same organ or of members of the same 

 whorl; for instance, to the union of the sepals in a 

 gamosepalous calyx, or of the petals in a gamopetalous 

 corolla. It may arise either from a union between 

 organs originally distinct, or more frequently from a 

 want of separation between parts, which under general 

 circumstances become divided during their develop- 

 ment. Nothing is more common as a normal occur- 

 rence, while viewed as a teratological phenomenon it is 

 also very frequent. For the purposes of convenience 

 it admits of. subdivision into those cases wherein the 

 union takes place between the branches of the same 

 plant, or between the margins of the same leaf-organ, 

 or between those of different members of the same 

 whorl. 



Cohesion between the axes of the same plant. This cohesion 

 may occur in various manners. Firstly. The branches 

 of the main stem may become united one to the other. 

 Secondly. Two or more stems become joined together. 



