THE PRINCIPLE OF NUMBER. 31 



as the case may be; this, Uaplophyllum may be compared with 

 Uuta, lluhia with Galium, or, again Fotentilla reptans with 

 P. Tormentilla, etc. On the other hand, I repeat, when one 

 observes that of the 71 genera of Eosacece three only are 

 recorded in the Gen. Plant, as having opposite leaves, and 

 these three are characterized as having 4-merous flowers, viz. 

 lihodotypus, EucrypJiia, and Coleogyne, there appears to be 

 a significant correlation between quaternary flowers and 

 opposite leaves. 



A quaternary arrangement is found very exceptionally 

 in Monocotyledons, as in the order Naiadacea3, e.g. Tetron- 

 cium and JPotamogeton. As the numbers 6 {i.e. 2 X 3), 4, 

 2, and 1 are found in different genera, the quaternary 

 as also binary arrangements may, I think, be reasonably 

 referred to symmetrical reduction. 



Perhaps of all orders the quaternary arrangement (at 

 least in part) of Crucifers has raised more discussion than 

 any other kind of floral symmetry. 



Without entering here upon any lengthened discussion 

 I would only add that, as far as investigations into the 

 anatomical structure of the pedicel is concerned, there is a 

 decided difference from what occurs in most flowers having 

 a definite number of parts, and where the whorls are 

 regularly superposed to one another, in that the members 

 of the whorls not being for the most part on common radial 

 planes, they have not their cords fused together in the usual 

 manner in a radial direction. 



A section at some distance below the flower reveals four 

 or five cords forming a circle. These rapidly increase in 

 number by branching laterally, till between ten and twenty 

 are found arranged in an oval just below the flower. Two 



* See my paper On the Structure of a Cruciferous Flower, Trans. 

 Lin. Soc, 2nd series, Botany, vol. i. p. 191. 



