MORPHOLOGY. 485 



development, the persistent union of parts, usually 

 separate in the adult state, has been traced to an 

 arrest of the process of development, by no means 

 necessarily coexistent with diminished growth. The 

 diminished or increased number of parts is, in like 

 manner, attributable to analogous causes, as also are 

 the variations in arrangement and form, spoken of 

 under the heads of Displacement, Peloria, Substitu- 

 tion, &c. 



In the instance of displacements, it has been shown 

 how slight a change is required to transform the so- 

 called inferior ovary into a superior one. A defective 

 development of the top of the flower-stalk in some 

 cases, in others a lack of union between the tube of 

 the receptacle or of the calyx (comprising in those 

 terms not only the apex of the receptacle, but the base 

 of the sepals) and the carpels, suffice to bring about 

 this change in a character which for systematic pur- 

 poses is of great value. 



Law of alternation. The circumstances that interfere 

 with the law of alternation may be briefly alluded 

 to. The deviations from the customary arrangement 

 have been very generally attributed to suppression, 

 or to chorisis. It is unquestionable that either of these 

 affords an efficient explanation of the arrangement in 

 question, as also does that modification of chorisis, as 

 it may be considered, which has been treated of under 

 the head of Enation. Spiral torsion of the axis would 

 likewise bring about analogous results. Still, it is quite 

 conceivable that opposition or superposition of organs 

 may occur without the intervention of any such opera- 

 tions. This will be the more readily conceded when 

 it is remembered that the phyllotaxis of leaves not 

 unfrequently varies on different branches of the same 

 individual tree, and that a similar variation in the 

 flower would at once disturb the customary alter- 

 nate arrangement. Coalescence of the vascular 

 bundles in an unusual manner, and an irregular dis- 



