e form of a thallus among
Cryptogams, but which in the higher groups of plants becomes marked out
into separate portions, each portion having its own distinct functions
to fulfil for the common benefit of the whole organisation.[556]

=Special morphology.=--Under this heading brief reference may be made to
some of the organs whose morphological nature has been, and still is,
much contested. It is clear that for the due elucidation of these
matters, development and the comparative investigation of similar
structures in different plants must be studied. Teratological data by
themselves can no more be trusted to give a correct solution of any
particular question, than the evidence furnished by other departments of
botanical science taken separately. With this statement by way of
caution, allusion may be made to some of the organs whose morphological
construction is illustrated by the facts recorded in the present
volume.

=Calyx-tube.=--In descriptive botany it is the common practice to speak
of a calyx-tube, by which is meant a tubular or sheathing portion at the
base of the flower, below the sepals or calyx-lobes, and distinct or
inseparable from the ovary. The question morphology has to solve is
whether this tubular structure is to be considered as a portion of the
axis, or whether it is to be regarded as composed of the confluent bases
of the sepals.

Mr. Bentham, who has recently reviewed the evidence as to the nature of
the calyx-tube in his paper on _Myrtaceae_,[557] still holds to the
notion that the "calyx-tube" or "hypanthium" is formed from the
concretion of the basal portions of the sepals. He founds his
conclusions upon such facts as the following: the circumstance that the
point of origin of the leaf is not always the same as the point of
disarticulation or separation from the axis, inasmuch as the basal
portion of the leaf is often adherent to the stem for some distance,
though still recognisable as foliar not axial in its nature. In the same
manner, the corolla and androecium may be concrete at the base, so
that the stamens are for convenience' sake described as inserted into
the tube of the corolla, though it is generally admitted that both
stamens and petals are really hypogynous, and it is not usual to
consider the corolla-tube up to the divergence of the stamens as part of
the receptacle. A similar remark applies to the carpels and placentas.
Mr. Bentham further considers that the gradual disconnecti