DARWIN ON PRIMULA. 239 



flowers of V. odorata to be quite infertile. In this sj)ecies, as in V. 

 hirta (which some botanists unite with it) it is the later flowers, 

 without corolla and with stamens of variable length, which give the 

 fertile capsules. Plants of the double violet he showed also bore 

 apetalous flowers. V. ericetorum was found to exhibit the same 

 phenomenon. This botanist concluded from his observations that 

 the species of the section Nominium* of the genus Viola have two 

 flowerings, the first vernal with well-developed petaloid flowers not 

 maturing seeds, the second aestival, with abortive corollas but always 

 fertile. The dimorphism in Viola has been more recently examined 

 by M. Michaletf and M. Miiller.J The former says that the earlier 

 of the ' apetalous' flowers ofler transitional forms between the two 

 states, which, however, he did not sufiiciently follow. The second 

 flowering lasts from the close of the first through part of the summer 

 even until autumn ; the May and June flowers being scarcely one- 

 fourth the size of the earlier ones. In these he finds the calyx to be 

 hermetically closed over the flower, leaving a large and empty space 

 above the ovary, which he considers may favour fecondation. The 

 sepals are afterwards burst open by the enlargement of the capsule. 

 The petals are not entirely absent but fall considerably short of the 

 sepals ; they are membranous and hyaline, occasionally they are re- 

 duced to one or two, hence the summer flowers are not correctly 

 described as truly apetalous. M. Michalet observes that he never 

 found the anthers open, even in flowers the ovary of wliich was cer- 

 tainly fertilized. The style is much shorter than in the ' petaloid' 

 flowers, the stigma truncate and funnel-shaped at top, the cavity 

 opening into the ovary. The stigmatic siu-face seems smooth and 

 not papillose. How fecondation is effected in these flowers he is 

 unable to say. 



A case parallel to the above is described by M. Michalet in the 

 Wood-sorrel {Oxalis Acetosella), with the difference that the early and 

 beautiful petaloid flowers are regularly fertilized, and produce perfect 

 seeds. In the second or summer flowers, the sepals are closely 

 applied and hermetically closed over the essential organs as in the 

 violet. The petals, usually of the normal number, are much shorter 

 than the sepals ; they are rarely all wanting. There are ten stamens, 

 of which five are smaller and appear quite barren ; the five larger 

 ones are fertile, and incline over the stigmas, with which they are 

 described as being aj^parently united by delicate filaments. The 

 part which these J)lay, M. Michalet is unable to explain. The 

 anthers appear to remain closed, and the pollen seems as it were 

 deliquescent. The seeds of the smaller flowers, which are rij^ened 

 luider the surrounding moss and detritus, offer no apparent differ- 

 ence from those of the normal ones. The same observer finds 



* Messrs, Hooker and Beutham in their " Genera Plantariim" attribute dimor- 

 phous flowers to all the sections excepting Mdaniuni, 



t Bull. Soc. Bot. France, vii. 465. J Bot. Zeit. 1857, 729. 



