Linnaan Society. 355 



at sotne 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 phsenomenon 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- 

 lopment of the interior circles stopping the circulation of the fluids, 

 and conceives this to be strikingly exemplified in Papaveracece, where 

 the growth of the petals within the bud is great and rapid. He no- 

 tices a specimen of Eschscholtzia 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 suppUes 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 Anagallis, 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 



