Thalamiflorae

In the preceding chapters I have endeavoured to give a general sketch of the relations existing between flowers and insects. I shall now proceed to describe particular instances more in detail, following in general the classification adopted in Mr. Bentham's admirable "Handbook of the British Flora," from which also many of my facts and illustrations have been borrowed. I propose to go through the English Flora, in the order of Mr. Bentham's work, calling attention to those facts, bearing on our present subject, which strike me as most interesting. The present chapter is devoted to the thalamifloral division of the Dicotyledons.

The vegetable kingdom may be divided into flowering and flowerless plants; while flowering plants again fall into two divisions, known as Dicotyledons or Exogens and Monocotyledons or Endogens. Dicotyledonous or exogenous plants are those in which, when the seed germinates, the "plumule" or bud arises between two (rarely more) seed-leaves or cotyledons of the embryo, or from a terminal notch. In this class the leaves have their nerves branched, forming a sort of network, as in the oak, beech, clover, violet, etc. In their growth they increase by forming new woody tissue over the old, whence the term "Exogenous." In a Dicotyledonous or exogenous tree, therefore, we find a number of concentric circles, each representing a period of growth, and indicating, though roughly, its age in years. Monocotyledonous or endogenous plants, on the contrary, are those in which the plumule or bud is developed from a sheath-like cavity on one side of the cotyledon. The leaves have parallel nerves, as for instance in grasses, orchids, lilies, palms, etc. In a cross-section the wood shows no concentric circles, but consists of bundles of woody fibre irregularly imbedded in cellular tissue. Both these classes have flowers.

Cryptogams, on the contrary (ferns, mosses, seaweeds, lichens, fungi, &c), have no flowers, and multiply by bodies called spores.

That the colour of the corolla has reference to the visits of insects is also well shown by the case of those flowers, which - as, for instance, the ray or outside florets of Centaurea - have neither stamens nor pistils, and merely serve, therefore, to render the flower-head more conspicuous. The calyx, moreover, is usually green; but when the position of the flower is such that it is much exposed/ it becomes brightly coloured, as, for instance, in the Berberry or Larkspur.

The above characters, though true in the main, do not hold good in all cases, For instance the genus Arum, though a Monocotyledon, has reticulated nerves, but its stem is endogenous, and its embryo has only one cotyledon.

The class of Dicotyledons is divisible into four subclasses, which may be thus characterised: Thalamiflorae. Petals distinct from the calyx and from each other, seldom wanting. Stamens usually hypogynous (i.e. attached under the ovary), so that if the calyx be torn away the stamens remain. Calycijlorce. Petals usually distinct. Stamens perigynous (i.e. attached round the ovary), or epigynous (i.e. placed upon the ovary). Corolliflorae or Monopetalce. Petals united (at least, at the base) into a single corolla. Incompletae or Monochlamydeae. Perianth or floral envelope, really or apparently simple; or none. These subclasses may be tabulated as follows: -

Perianth or floral envelope

single or none ............................

Monochlamydeae

double

corolla of united petals ....

Corolliflorae.

corolla of dis-tinct petals

stamens hypo-gynous

Thalamiflorae.

stamens perigy-nous or epigy-nous . .

Calyciflorae.