218 COMPOSITAE. 
racterised by having all its flowers ligulate. This is a ques. 
‘tion worthy of examination, for it appears to my limited 
experience, that in both those tribes which are characterised 
by having entirely regular, or entirely labiate flowers, that 
the amount of pressure due to the structure of the involu- 
crum is greater than in the third or mixed tribe. 
It must not be overlooked that the degree of development 
of ligulate flowers, is in the ratio of their distance from 
the centre. 
The maximum growth isia most cases around the cer- 
cumference; take for instance Centaurea, and this may 
also be looked upon as an evidence in favour of the gene- 
ral tendency to produce ligulate circumferential flowers. 
This tendency is very evident in Calendula vulgaris, in certain 
specimens of which, but very few flowers in the centre 
of the disc remain unchanged, and it is equally so ina 
vast number of others, in which, although the flowers of 
the circumference are less developed than those of the 
centre, yet there ‘is an obvious tendency to become 
unilabiate. The two lacinez that in Calendula take on the 
irregular growth are the two nearest the axis, and it 
appears to be a condition, and indeed one without which 
the lip would have a reversed directions, that while they 
continue entirely distinct from each other, they cohere 
more or less with the teeth nearest to them, Thus when- 
ever a lacinea is wanting, it is the 5th. 
The tendency to ligulation is always accompanied by à 
higher degree of coloration. Thus in Calendula, the first 
change that takes place consists in the lacinie nearest 
the axis, or their inner halves with respect to the axis, 
assuming an orange, in lieu of their original yellow colour. 
Granting the tendency to separation between these tw? 
lacinie, and a tendency to adhesion or even obliteration 
of all or part of the others, the corolla must necessarily 
become more or less unilabiate, particularly when com" 
bined with a certain extra development. 
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