ARRANGEMENT OF THE PARTS OF THE FLOWER. 467 



be in advance of the petals, that appearance is due to the growth 

 of the stamens overtaking that of the petals, and not to any out- 

 growth from the stamens. Tor instance, in Lysimachia vulgaris^ 

 in some other Primulacese, I find that in the course of develop- 

 ment the petals lag behind the stamens, and hence allow more 

 room for the development of the latter. The pistil is developed 

 in the shape of a cylindrical tube, and shows no sign of cohesion 

 of carpels, but rather of a lack of separation of those organs. In 

 some cases, however, the carpels do become separated. 



A similar explanation to that given by Pfeffer in the case of 

 Primroses has been offered with regard to some Hypericaceae and 

 Plumbaginaceae ; and by others in the case of those Malvales 

 wherein the stamens are antipetalous, but, as it would seem, on 

 questionable grounds. The history of development, so far as 

 known, and the analogies with the structure of other Malvales 

 render it more probable that the superposition is due to abortion 

 or to some other cause rather than enation*. 



The peculiar position of the styles of Aristolochia, superposed 

 to the stamens, is explained by Payer on the supposition that 

 the styles are mere outgrowths from the stamens to which they 

 are superposed. (See Mast, in Journ. Linn. Soc. xiv. p. 488.) 



It seems desirable to draw a distinction between Enation and 

 Chorisis, although in the adult flower the difference between the 

 two processes may not be always obvious f- By the process of cho- 

 risis the original organ is repeated, petal follows petal in the same 

 way that the leaves of a book do. The process begins at a very 

 early stage of development ; and it is often difficult to ascertain 

 whether the younger growths are independent productions 

 from the floral axis, or secondary growths from the preexisting 

 lateral organs. In the case of enation the process is subsequent 

 to the first stages of development; development has made 

 some progress before the outgrowth is observed. In the case of 

 chorisis, the organ is repeated ; in enation it generally happens 

 that the new growth is of a different appearance from, and fre- 

 quently has a different office to fulfil than that of, the part from 

 which it springs. The scales before the petals in Silene, in CoroJcia, 



Van Tieghem (Kecherches sur la structure du pistil, p. 14) considers that 

 the petals of Mallows are stipulary appendages of the staminal leaves ; so that, 

 ding to him, there are but two whorls in a mallow-flower — asepaline whorl 



acoo 



bears both stamens and petals, and a carpellary whorl opposite 



See also this author's translation of Sachs's Traits, p. 622. 



343 



