THEORY OF THE STRUCTURE OF PLANTS. doo 
my being found unequal to the difficulties of the case. I am however, 
giving you speculations which have occasionally occupied me during 
a number of years and which are founded on cautious and repeated 
observations of facts, not without study of the judgments pronounced 
by writers of authority which I desire to treat with respect whilst 
I freely examine their merits. 
Our first inquiry relates to the real nature of the order of the 
parts of the flower in a tribe of plants well known as cruciform 
flowers, and familiar from the wall-flower, stock, cabbage, and several 
common weeds constituting the order Brassicaceae of Lindley. 
Plants of this order are distinguished by a very peculiarly constructed 
seed-vessel divided: into two cells by a partition which is not easily 
brought into analogy with anything in the ordinary constitution of 
seed-vessels, and whilst the calyx and corolla consist of four parts 
each in the usual relative positions, the number of parts in the 
Gynoecium or ovary, is apparently only two, and the androecium 
shows six stamens in two pairs with a single lower oue at each end. 
Now it is well known to all who have attended to the subject, that 
every flower consists of circles of leafy organs variously modified 
in their development, the inner circle consisting of what are now 
ealled carpels, of which the apex is the stigma, and the margin 
usually at least bears the ovules—next follows the circle of stamens, 
often indeed several circles, each stamen consisting of a filament 
corresponding to the mid rib of the leat, and an anther most 
‘commonly of two cells formed from its expansion, the parenchyma of 
‘one surface being converted into pollen grains. Outside the stamens 
occur the petals, or inner enveloping circle, and outside all the calyx, 
consistizg of pieces called sepals. Now it is the general rule that 
these circles alternate one with the other in regular order, {he inner 
circle being indeed peculiarly liable to have its number of partsreduced 
by pressure, and the others exhibiting occasional anomalies from ad- 
herence, irregularity and suppression or abortion, either of a whole 
circle or some part of it. Hvery flower is formed on a certain definite 
plan as to the number of circles and of parts contained in each, and 
as to their relative position, and when there is any deviation from equal 
numbers and alternate arrangement we always expect to be able to 
offer some explanation which shall shew it to be a case naturally arising 
under the general law. Although five is the natural number of parts in 
each circle in Exogenous plants, it is by no means unusual! to meet 
