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 the 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 fusion), and that pressure will imduce the 
coalition of organs primarily distinct. 
CHA PPE RR? IT: 
COHESION. 
Fottowrne Augustin Pyramus De Candolle, 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 
eamosepalous 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 whereim 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. 
