26 COHESION 
of the cohesion of the margins at the base and apex 
of the leaf, which thus appears perforated. This ap- 
pearance, however, 1s probably due to some other 
cause. When the leaves are verticillate and numerous, 
and they become coherent by their margins, they form 
a foliaceous tube around the stem. When there 
are but two opposite leaves, and these become united 
by their margins, we have a state of things precisely 
resembling that to which the term connate is apphed. 
Fusion of the edges of the cotyledons also occasion- 
ally takes place, as in Hbenus cretica.t It has also 
been observed in Tithonia, and is of constant occur- 
rence in the seed leaves of some Mesembryanthema. 
This condition must be carefully distinguished from 
the very similar appearance produced by quite a dif- 
ferent cause, viz., the splitting of one cotyledon into 
two, which gives rise to the appearance as if two were 
partially united together. 
Some of the ascidia or pitcher-like formations are 
due to the cohesion of the margins of two leaves, as in 
a specimen of Crassula arborescens, observed by C. 
Morren. 

Fic. 10.—Two-leaved pitcher of Crassula arborescens, after C. Morren. 
The stipules may also be fused together in different 
' De Candolle, ‘ Mém. Lég.,’ pl. v, fig. 14. 
