178 THE REV. G. HENSLOW ON THE ORIGIN OF FLORAL ASTIVATIONS. 
Little attention, indeed, appears to have been paid to :estivations until that eminent 
botanist called attention to their importance *. Since then nearly all text-books describe 
the principal forms, but without tracing any or but slight connexions between them. 
If we turn to our latest authorities, we find Le Maout and Decaisne, for example, 
devoting two pages (86, 87) to the subject in describing, as usual, the different kinds, 
and also attempting to explain the “ papilionaceous " and ** cochlear” by, as I believe, а 
wrong application of the “ quineunx ;" while in Sachs's * Text-book of Botany,’ “ sestiva- 
tion," “ imbricate,” * contorted,” and “ valvate," are words conspicuous by their absence 
from the index as well as from the text. Many diagrams occur in that work; but the 
subject of zestivation seems to have been totally ignored. 
The laws of phyllotaxis have to some extent been adapted to the floral whorls, more 
especially and obviously to the quincuncial or ? plan. The very frequent occurrence of 
this latter amongst sepals and petals is of itself a sufficient indication that phyllotactical 
laws are in certain cases applicable—as also the fact that the outer whorls of flowers are 
in some cases composed of many parts and spirally arranged, especially when there is no 
manifest “break” between the whorls, as in Calycanthus, Cactus, &c. Іп these cases 
the $, 3, 7s, and even зг arrangements may be detected. 
II. THE Forms оғ ÆSTIVATION, 
The following include those usually described, аз well as one or two in addition. 
1. Distichous equitant, or the 4 arrangement in which one of the two opposite parts 
overlaps the edges of the other, as in Papaver (Tab. XXV. fig. 1). 
The half-equitant is a modification of this, in which one edge of each part overlaps one 
of the edges of the other part respectively, as in the calyx of Poppy and the corolla of 
Circea (Tab. XXV. fig. 2). 
2. Tristichous or the X arrangement. This is especially characteristic of Mono- 
cotyledons. It may be observed that it is identical with the “ imbricate proper" when 
the whorl has only three parts, so that the first overlaps the second, and the latter 
overlaps the third, which last also underlies, with its opposite edge, the first (Tab. XXV. 
fig. 3). 
3. Pentastichous, quincuncial or 2 arrangement, in which the parts of the whorl cor- 
respond with those of one projected ** cycle” of that plan (Tab. XXV. fig. 4). 
4. Half-inbricate.—l apply this term to а large number of instances ranging from 
complete regularity to such extremely irregular forms as the corollas of the Violet, the 
Pea, and the Snapdragon. It is produced by a slight modification of the quincuncial— 
namely, by the edge of the second part being overlapped by instead of itself overlapping 
the fourth part (Tab. XXV. fig. 5). 
5. Imbricate propert, in which the parts of а whorl overlap each other in succession, 
* А short summary of the history of the nomenclature of sestivations has lately appeared from the pen of Prof. А. 
Gray, іп the American Journal of Sciences and Arts, vol. x. Nov. 1875, and is reprinted in the Journal of Botany, 
new series, vol. v. p. 53. 
+ І call this “ imbricate proper," as the word “ imbricate” is also used technically for an indefinite number of parts, 
as in the scales of Calycanthus &c., which overlap like tiles on a roof. Linnæus appears to have included all these 
forms (viz. 3, 4, 5, and 6) under this term (see Prof. Gray's paper 1. с.). 
