[177 J 
XI. On the Origin of Floral ZEstivations. With Notes on the Structure of the Cruciferous— 
Flower, on that of Adoxa, and on the Corolla of Primula. Ву the Rev. G. Henstow, 
M.A., F.L.S., F.G.S. 
| (Plate XXV.) 
Read June 1st, 1876. 
INTRODUCTION. 
THE idea of endeavouring to trace out any laws that may exist amongst floral æsti- 
vations arose in my mind from observing the large number of diagrams given in Le 
Maout and Decaisne’s * Descriptive and Analytical Botany, in which the æstivations 
of about 250 genera of Dicotyledons and of 50 of Monocotyledons are diagrammatically 
expressed. I therefore proceeded to draw up an enumeration of all the different kinds, 
and to ascertain what percentage each had amongst the genera, and what connexions 
there might be amongst those different kinds. I then examined a number of living 
flowers of several genera, but soon found my work had been to some extent inefficient as 
based upon very insufficient data *. 
So far from each diagram given being the sole example or even always typical of a 
genus, I found it to be the commonest thing for a species to have a very considerable 
amount of variation, as will be seen at the close of this paper. As an example, the 
diagram of Primula, p. 529 (Engl. ed.) 4, is not the only kind, as this genus can boast of 
at least eight varieties in the Primrose alone. Again, the diagram of the male flower 
of Hydrocharis, p. 154, does not correspond with the figure of the flower given there, in 
that the inner whorl of the figure is “ tristichous," while it is represented as “ con- 
volute " in the diagram. Lastly, two diagrams of Hermannia are given on p. 284, as if 
it were an unusual occurrence for a flower to have its whorls running spirally in opposite 
direetions, whereas it is an extremely common occurrence. Hence, if any one should 
be led to imagine these diagrams to be in all cases characteristic or the sole kinds of 
æstivation peculiar to each genus respectively, he will be much mistaken. It may be 
observed, however, that nothing is said respecting them whatever, as to whether they do 
represent typical forms or not. Оп the other hand, the estivations of many genera 
are remarkably constant, such as the universally **convolute to the left” corolla of 
Myosotis; or again, the valvate calyx with contorted corolla of Mallow, though even 
here the “ imbrication"' may be either to the right or left; and when this is the case, it 
may become, as Robert Brown pointed out, a valuable diagnostic character. 
* The draught of this paper was made on recovering from a long illness, when I had but few opportunities of 
testing the conclusions given from the study of the diagrams alone. I, however, give these conclusions, because the 
reader will be able to refer to the diagrams in that excellent work, and because the deductions made from a comparison 
of those diagrams is generally very similar to that derived from the examination of the variations in the flower-buds 
of living plants. Sets 
t The references to pages throughout this paper always refer to Le Maout and Decaisne's work. 
SECOND SERIES.—BOTANY, VOL. I. 2c 
