16 THE STRUCTURE OF FLOWERS. 



that the J and |- types are exceedingly common in the foliage 

 of Monocotyledons, while the -|, as far as I am aware, is 

 entirely wanting in that class, whether in foliage or flowers. 



Of genera having alternate leaves bat associated with a 

 binary or quaternary floral symmetry, there are about 270 in 

 aumber of about 30 orders. Now, the co-existence of alternate 

 leaves with 2- or 4-meroiis flowers appears at first sight to 

 negative the theory ; but, as mentioned above, these and 

 other irregularities have been brought about by subsequent 

 differentiations in the foliage or flowers. On the other hand, 

 opposite leaves with quaternary flowers are not at all in- 

 frequent, though not quite so common as when they are 

 alternate ; thus, Oleacece and Onagracem are so conditioned. 

 Again, in liosacece, which is an order characterized by having 

 alternate leaves and 5-merous flowers, three genera alone 

 out of seventy have opposite leaves, and these three also are 

 accompanied by 4-merous flowers ; viz. BhodotypuSy Coleogyne, 

 and Eucrypliia. These three genera thus acquire their 

 importance from being isolated amongst others to which 

 they are allied, and which are generally otherwise charac- 

 terized. Many orders have both foliage and floral symmetry 

 remarkably inconstant, and all four combinations, viz. 4- 

 merous and 5-merous flowers with opposite or alternate 

 leaves almost indiscriminately, as in the tribes Biosmece and 

 BorosmecB of Butacece ; and it is a noticeable fact that, 

 associated with this inconstancy of correlation, there is an 

 inconstancy in the leaf arrangement, opposite and alternate 

 leaves being often in species of the same genus, and even on 

 the same individual plant. 



The total number of genera noticed as having 4-merous 

 flowers and opposite leaves was 110 in 25 orders ; whereas 1 

 noticed 276 genera of 30 orders as having 4-merous flowers 

 associated with alternate leaves. This, I believe, is due to 



