BRACTS AND FLORAL LEAVES. 83 
Thus the members of contiguous whorls (e.g., sepals and petals) 
alternate with one another, while the members of alternate whorls 
are superposed, 2.e., are in the same rank or orthostichy. There 
are ten ranks in the example supposed. Comparatively few 
flowers are constructed so regularly as this, but a great many 
can be explained by supposing alterations to have taken place 
either in the number of whorls or the number of parts in certain 
whorls. Very commonly both kinds of change appear to have 
happened. Abundant examples will be found in the sequel. 
We have now to consider in detail calyx, corolla, andreecium, 
and gynecium. Five headings may be conveniently taken in 
each case, viz., Number and Arrangement, Cohesion (union of 
like parts), Adhesion (union of unlike parts), External Charac- 
ters, and Structure. 
The Catyx, or outer whorl of the perianth, departs less from 
the foliage leaves in nature than any other part of the flower, 
and a gradation may sometimes be traced between sepals and 
such leaves. In the dog-rose, for example, there are five sepals 
arranged in a very short spiral. The two or three lowest bear 
small leaflets in a pinnate manner, thus resembling the pinnate 
foliage leaves of the same plant. 
Number and Arrangement.—In acyclic flowers, such as those of 
Cacti, the spirally arranged sepals may be indefinite in number, 
and pass, on the one hand, into bractlets, on the other, into 
petals. The cyclic and hemicyclic flowers of dicotyledons are 
generally characterized by the numbers five and four (or multiples 
of the same). The former number very frequently indeed goes 
with a phyllotaxis of two-fifths. Examine once more the wild 
rose. The foliage leaves are here arranged with the above 
divergence (cf. p. 50), which means that each cycle includes 
five leaves and turns twice round the stem. The five-leaved 
calyx is here just such a cycle telescoped, but the spiral arrange- 
ment can still be made out. A little further change would alto- 
gether obliterate the spiral, and give us a whorl of five members, 
as in buttercup. The number four is found in wallflower, stock, 
shepherd’s purse, and many other plants. An examination of 
the calyx in a wallflower will show that the sepals are in two 
alternating whorls, each containing two sepals. This may per- 
haps correspond to the opposite decussate arrangement found in 
foliage leaves (p. 49). In wallflower, however, the foliage leaves 
are not arranged in this manner, which fact tells against the ex- 
planation. Three (or a multiple of it) is by far the commonest 
number among monocotyledons (fig. 37). The three large white 
sepals of snowdrop furnish a striking example. This number is 
associated, as might be expected, with a phyllotaxis of one-third. 
