tubercles, thickly clothed with deformed leaves, and invested by a vast
number of hairs, longer and more dense than usual. A similar deformity
sometimes occurs in an Indian species of _Artabotrys_; in these
specimens the branchlets are contracted in length, and bear numerous
closely packed scaly leaves, densely hairy, and much smaller than
ordinary.

Spines and thorns may he looked on as atrophied branches, and seem to
result from poorness of soil, as the same plants, which, in hungry land,
produce spines, develop their branches to the full extent when grown
under more favorable conditions.[523]

In the birch an arrest of development in some of the branches is of
common occurrence. The branch suddenly ceases to grow in length; at the
same time it thickens at the end into a large bulbous knob, from which
are developed a profusion of small twigs, whose direction is sometimes
exactly the reverse of that of the main branch. (See p. 347.)

The branches of the common spruce fir, especially the lateral ones, when
attacked by a particular species of aphis, are very apt to be developed
into a cone-like excrescence.[524]

A shortened condition of the flower-stalks occurs occasionally, greatly
altering the general character of the inflorescence. This has been
observed in pelargoniums and in the Chinese primrose, in both of which
the effect was to replace the umbellate form of inflorescence by a
capitate one.

=Abortion of the receptacle.=--Here may be mentioned those cases of
flowers with habitually inferior ovary (real or apparent), in which the
receptacle fails, from some cause or other, to dilate as usual. This has
already been alluded to under the head of Prolification, Displacements,
&c. (pp. 78, 130, &c., figs. 35-37, 64, &c.), and hence requires only
incidental comment in this place. There are, however, certain other
cases of a similar nature which may here be referred to; such as the
abortive condition of the inferior ovary, or rather of the receptacle,
that usually encircles the ovary in _Compositae_ and _Umbelliferae_. In
the former natural order the following plants have been met with in this
condition:--_*Tragopogon pratense!_, *_Cirsium arvense_, _Hypochaeris
radicata_, _Senecio vulgaris!_, _Coreopsis Drummondi_. In the latter
order, _Daucus Carota!_ _OEnanthe crocata!_ and _Thysselinum
palustre_, seem most frequently to have been observed in this
state.[525] In some gourds the receptacle may be seen partially
d