773 



"With respect to the fall of the leaf, he refers to the observations of 

 DeCandollie and Du Petit Thouars, which he does not think sufficient 

 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 caducous, to the 

 outward pressure occasioned by the more rapid development of the 

 interior circles stopping the circulation of the fluids, and conceives 

 this to be strikingly exemplified in Papaveraceae, where the growth of 

 the petals within the bud is great and rapid. He notices 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, re- 

 mains after the opening of the flower partially adhering ; 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 organs supplies the force which se- 

 parates the part of the coherent sepals 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 prepared to offer any opinion. 



" In the fruit, as in the calyx, the author believes that horizontal dis- 

 ruption arises from the force of cohesion of the parts of the circle, the 

 absence of any of the causes favourable to dehiscence along the mid- 

 rib of the carpellary leaf, and the operation of some force pressing 

 either from without or from within on one particular line encircling 

 the fniit ; and he proceeds to offer explanations of those cases with 

 which he is most familiar. He lakes first the circumscissile capsule 

 of Anagallis, in which he states that the central free receptacle with 

 the seeds upon it continuing to enlarge in both diameters after the en- 

 velope has ceased to grow, and having occupied from the first the en- 

 tire cavity, it is naturally to be expected, since the chief extension of 

 the interior parts is upwards (the natural direction of growth), while 

 the enlargement of the seeds in the lower half tends to press back the 

 parts of the lower hemisphere, that uniform and regular pressure will 

 resolve a nearly spherical capsule into two equal hemispheres. This 

 remark he applies to Centunculus also, but confesses himself at a loss 

 to give any reason why the opening of Trientalis, which depends on 

 the same general causes, should be irregular. For the separation of 

 the lid of the capsule in Hyoscyamus he accounts by the contraction 

 Vol. II. 5 e 



