ON CHORISIS. 379 



with and harmonises ail the facts so as to he received as what we call 

 « good explanation of them. The kind of facts which chorisis under- 

 takes to explain are cases in which the symmetry of the flower as 

 eommonly understood would suggest the expectation of one organ, 

 but we actually find two or more, and these in an unusual degree of 

 proximity ; cases in which the multitude of apparently distinct organs 

 produced in close proximity seems inconsistent with the supposition 

 of their belonging to successive circles ; those in which a number faf 

 exceeding the natural number seems to be found distinctly in one cir- 

 eie, and those in which a number of similar organs are combined at 

 their base in clusters, the number of clusters corresponding to what 

 might have been expected to be the number of organs. All these are 

 represented as being capable of explanation by collateral chorisis or the 

 Bubdivision laterally of one organ into a number of organs. There ia 

 also a different class of facts, such as the occurrence of organs arising 

 on the face of other organs and opposite to them : sometimes of lines 

 of opposite organs, which being supposed inconsistent with other 

 principles of structure, are explained as cases of transverse chorisis, 

 or the division of a single organ into folds like the splitting of a card 

 into two or even many similar or related organs. It cannot be denied 

 that the cases to which chorisis has been applied as an explanation are 

 attended with some difficulty, and that some of them are even incapa- 

 ble of plausible explanation by previously established principles* 

 Some of them, however, appear to me quite consistent with those prin- 

 ciples, as I shall endeavour to show when examining some alleged 

 examples, and although it cannot reasonably be affirmed that such an 

 operation as chorisis is inconceivable as arising from the nature of the 

 organs of the flower, and it seems even to be sanctioned by some facts, 

 yet I find myself obliged at least to limit its application within much 

 narrower bounds than some able botanists have assigned to it. My rea- 

 sons will be best given in an examination of the particular cases brought 

 forward at least a sufficient number of them to justify a general opinion 

 on the subject. I shall take the examples given by Dr. Gray, who 

 adopts fully the theory of chorisis in his valuable work, the Botanical 

 Text Book, pp. 250-255, having reference also to his remarks in " The 

 genera of the United States Flora, illustrated." Dr. Gray's first ex- 

 ample of collateral chorisis, on which he is disposed greatly to rely, is 

 found in the Tetradynamous stamens of the natural family Brassica- 

 «c«. This case I considered at large in a paper read before the Cana- 



