46 



NA TURE 



\_Nov. 20, 1873 



tion,* and which he has interpreted as a guide-marlc 

 for those visitors, wliich are diminutive enough to crawl 

 entirely into the flower. This streak is also wanting in 

 the small-flowered form (Figs. 18, 20), 



(4) In the large- flowered form pollen-grains do not 

 spontaneously fall out of the anther-cone before the flower 

 has been fully developed for several days ; whereas in the 

 small-flowered form, in by far the majority of cases, a great 

 number of pollen-grains fall spontaneously out of the 

 anther-cone into the stigmatic cavity and there develop 

 long pollen-tubes, even before the opening of the flower, 

 in much rarer cases a short time after it has opened. 



(5) When the visits of insects are prevented by a fine net, 

 the flowers of the small-flowered form wither two or three 



Fig. 15.— Front view of the more 

 natural size. Fig. i6. — Front 

 Fig. 17.— Pistil of Fig. 15, viev 

 size. Fig. 18.— Pistil of Fig. il 

 of Fig 15. Fig. 20.— Lateral vi 



The following explanation of the I( 



a, anthers : a}, upper, «-, lateral, 1 



upper sepal ; h, beard, i e. tuft of h.- ' 



conspicuous flower of Viola tricolor, 

 iew of the less conspicuous flower, 

 d on the under side, 12 times natural 

 Fig. 19 —Lateral view of the pistil 

 w of the pistil of Fig. 16. ^,. 



tering applies to all the figures : — 

 *, lower anther : ap^, appendage of the 

 i on the lateral surface of the skull-like 

 crest of the style ; c, appendage of the connective \fi, filaments ; k, knob of the 

 stigma ; /, lip, labiatcd appendage of the stigmatic opening : «. nectary, i.e. 

 honey-secreting appendage of the lower filaments : op, opening of the anther- 

 cone : ov, ovary ; /, petals ; /', lower, /-, lateral, p^, upper petal ; po, pollen- 

 collecting hairs ;/>-, protective hairs (Sprengel's " Saftdecke ") : s, .sepals; 

 J^, upper sepal (witli the appendage rt/ ) : s-, lateral sepal ; sp, the upper- 

 most part of the spur, containing the honey : st, stigmatic cavity : sir, 

 streaks converging: towards the opening of the flower : sty, style ; w, wedge- 

 shaped streak of the style ; y, yellow coloured part of the lower petal. 



days after opening, everyone setting a vigorous seed- 

 capsule ; those of the large-flowered form remain in full 

 freshness more than two or three weeks, at length wither- 

 ing without having set any seed-capsule ; when fertilised 

 they wither also after two or three days. 



Sttmmary : — The more conspicuous flowers of Viola 

 tricolor are adapted to regular cross-fertilisation by Lepi- 

 doptera, Apid.i;, and Rhingia ; whereas self-fertilisation 

 by these visitors is prevented. Pollen-eating flies and 



* In his interesting article on the Fertilisation of the Wild Pansy, Naturp, 

 vol. vni. p. 49. 



diminutive insects crawling into the flower may effect 

 both self- and cross-fertilisation ; fertilisation by insects 

 is possible from the opening of the flower for twenty 

 days or more ; spontaneous self-fertilisation never takes 

 place. On the contrary the less conspicuous flowers are 



Fig. 21.— Lateral view of Fig. 15 after the half of its sep.als and petals 

 having been removed, 7 times natural size. 



adapted to regular self-fertilisation ; although visited now 

 and then by the same insects as the more conspicuous 

 flowers, cross-fertilisation by these visitors is by no means 

 secured ; in most cases it is even prevented by the 

 pollen having previously fallen into the stigmatic cavity; it 



Fig. 22. — Lateral view of Fig. 16, but one lateral anther and the half of one 

 lower anther have been removed and the pistil bisected longitudinally. 



is possible only in those cases where the flower has 

 opened before its pollen has filled the stigmatic cavity ; 

 and even in tliese rare instances the possibility of cross- 

 fertilisation lasts but a few hours. 

 Lippstadt, October 1S73 Hermann Muller 



