2i6 ANGIOSPERMAE—DICOTYLEDONES 



545. L. usitatissimum L. (Sprengel, 'Entd. Geh.,' p. 175; Hildebrand, 'Die 

 Geschlechtsvert. b. d. Pfl.,' p. 75; Herm. Miiller, 'Fertilisation,' p. 148, ' Weit. 

 Beob.,' II, p. 219.) — The bright blue flower, according to Hermann Miiller, possesses 

 a mechanism which completely agrees with that of the last species. But being 

 more conspicuous, insect-visits are more numerous, so that crossing takes place 

 more frequently. Hildebrand has proved that when automatic self-poUination occurs 

 it is effective. 



Visitors. — Sprengel saw a humble-bee ; Herm. Miiller observed bees — Apis, 

 Halictus cylindricus F. — and Lepidoptera — Plusia gamma L., Pieris rapae L. ; 

 MacLeod noticed one humble-bee and a Muscid in Flanders (Bot. Jaarb. Dodonaea, 

 Ghent, vi, 1894, p. 239). Cf. L. grandiflorum. 



546. L. tenuifolimn L. — Kerner says that the slightly odorous rose-red 

 flowers of this species fall off as early as the second day of anthesis. According 

 to Kirchner (' Beitrage,' pp. 29-30), who studied the mechanism of the flowers 

 in Wallis, they agree with those of L. usitatissimum as regards homogamy, and 

 the secretion and concealment of nectar, but from the relative positions of the 

 stigmas and anthers — which mature simultaneously — the regular occurrence of cross- 

 pollination may be inferred. Owing to the conspicuousness of the flowers, which 

 have a diameter of 22 mm., this is sure to take place. The five styles which spring 

 from the ovary diverge, while the five filaments — united together below — stand erect 

 between the styles, and at the same level as the stigmas, which are outside them, and 

 at a distance of 3 mm. Even if towards the end of anthesis the petals and styles 

 come into contact, automatic self-pollination does not as a rule take place, for the 

 stigmas are at a higher level than the anthers in the closed flower. 



547. L. Lewisii L. — Planchon states that each plant of this species bears three 

 different kinds of flower, possessing medium, long, and short styles, respectively. 



548. L. austriacum L. — 



Visitors. — Friese observed Andrena braunsiana Friese in Hungary; v. Dalla 

 Torre saw the bee Osmia leucomelaena K. J and 5 in the Innsbruck Botanic Garden, 

 and Schletterer noticed it in the Tyrol. 



549. L. grandiflorum Desf. — This species was the starting-point of Darwin's 

 research • On the Existence of Two Forms and their Reciprocal Sexual Relations in 

 several species of the genus Linum' (1863). He showed that fertility was greatest 

 when the long-st)'led variety was crossed with pollen from the short-styled one, 

 and vice versa. Darwin's investigations also demonstrated that the short-styled 

 variety was more fertile when self-fertilized than the long-styled one, which was 

 almost self-sterile. When both kinds of pollen were put upon one kind of stigma, as 

 a rule only that germinated which was derived from the opposite sort of flower, 

 while that from the same sort either failed to germinate, or did so only to a 

 slight extent. 



Visitors. — Frey-Gessner observed two bees — Nomia diversipes Ltr. and 

 Systropha curricornis Scop. — in Switzerland. Plateau noticed that small Syrphidae 

 went straight from the red flowers of L. grandiflorum to the blue ones of L. 

 usitatissimum. 



