Linnean Society. 855 
at some other part of the organ, a portion separating from the rest, 
or the whole breaking up into pieces. Every such separation, he 
argues, must depend on one of the three following causes: 1. on a 
stoppage of the circulation from ligature; 2. on unequal rapidity of 
growth of the two parts; or 3. on the confinement within coherent 
envelopes (which do not admit of extension) of a portion of the axis 
or of some growing part, so that the force of growth bursts the en- 
velope, carrying off its upper portion. ‘These general rules he then 
proceeds to apply to the explanation of particular cases. 
Of stems usually termed Articulate, some, such as those of Kleinia 
articulata, have no tendency to disruption at the supposed joint, 
which is merely the commencement of a new branch. In the misletoe, 
on the other hand, the author believes that the tendency to divide at 
the bases of the branchlets may be consequent on the dichotomous 
structure, which causes a pressure equivalent to a ligature at the 
point of division. 
With respect to the fall of the leaf, he refers to the observations 
of DeCandolle and Du Petit Thouars, which he does not think suffi- 
cient to account for that phenomenon in a multitude of cases, but 
regrets that he can throw no additional light on the subject. He 
attributes the separation of the sepals and petals when they are ca- 
ducous, to the outward pressure occasioned by the more rapid deve- 
lopnient of the interior circles stopping the circulation of the fluids, 
and conceives this to be strikingly exemplified in Papaveracee, where 
the growth of the petals within the bud is great and rapid. He no- 
tices a specimen of Hschscholitzia in which the sepals cohering less 
firmly than usual, the calyx, instead of being thrown off in the form 
of a calyptra, remains after the opening of the flower partially adhe- 
ring ; and observes that the ordinary disruption in this genus takes 
effect, not at the base of the sepals, but at a point above this, where 
the pressure occasioned by the enlargement of the petals is greatest. 
He instances also the genus Eucalyptus, in which there is a strong 
coherence of the sepals, and the lower portion of the calyx being 
strengthened by the adherent torus, the growth of the interior or- 
gans supplies the force which separates the part of the coherent se- 
pals above the torus in a solid piece like the cover of a vessel. On 
the cause of the horizontal separation of a portion of the anthers in 
the form of valves, which occurs in a few instances, he is not pre- 
pared to offer any opinion. 
In the fruit, as in the calyx, the author believes that horizontal - 
disruption arises from the force of cohesion of the parts of the circle, 
the absence of any of the causes favourable to dehiscence along the 
midrib of the carpellary leaf, and the operation of some force press- 
ing either from without or from within on one particular line encir- 
cling the fruit ; and he proceeds to offer explanations of those cases 
with which he is most familiar. He takes first the circumscissile 
capsule of Azagailis, in which he states that the central free recep- 
tacle with the seeds upon it continuing to enlarge in both diameters 
after the envelope has ceased to grow, and having occupied from the 
first the entire cavity, it is naturally to be expected, since the chief 
