SAXIFRAGEAE 419 



xxxviii, 1896.) — In this species the free part of the receptacle is lo-ii mm. long, 

 fonning a tube \vhich is prolonged another 3 mm. by the erect petals. The nectar 

 is therefore only accessible to long-tongued bees, and the flowers belong to class Hh. 

 In other respects their mechanism agrees with that of R. rubrum. Warnstorf 

 describes them as protogynous : the stigma matures in the bud, and is very sticky. 

 The style projects beyond the stamens, so that autogamy is prevented. The pollen- 

 grains are white, irregularly roundish-tetrahedral, up to 41 /x in diameter. 



The flowers are at first bright yellow, but become carmine-red in colour when 

 the style and anthers have withered. Delpino was the first to attempt an explanation 

 of this colour-change : he thinks that it enables insect visitors to recognize flowers 

 which are over, thus being spared fruitless eff"orts to get nectar. Hermann Miiller 

 justly objects to this explanation on the ground that, if it were correct, flowers 

 exhibiting colour-change would have no advantage over those which wither or 

 fall ofl' immediately anthesis is over. The persistence and brighter colouring of 

 flowers that are over are better explained as serving primarily to enhance the con- 

 spicuousness of the inflorescences as a whole, so that insects are attracted in greater 

 numbers, though the fact that flowers which have completed anthesis are readily 

 recognized as such gives maximum value to the adaptation. 



Visitors. — Herm. Miiller saw Anthophora pilipes F., skg., easily inserting its 

 proboscis (20 mm. long) into the base of the flower. Delpino records the same bee 

 lor Italy, and 1 have noticed it in the Kiel Botanic Garden. Warnstorf also observed 

 bees. 



Alfken gives the following for Bremen. — 



Hymenoptera. Apidae: i. Andrena apicata .Vw. 5 ; 2. A. nigroaenea .ff. S ; 

 3, A. varians K. S; 4. Nomada borealis Zett. $; 5. Osmia rufa Z. }. B. Diptera. 

 Muscidae : 6. Cynomyia mortuorum Z. 



Gerslacker noticed the bee Osmia aurulenta Ps. S, freq., at Berlin. 



988. R. sanguineum Pursh. (Herm. Muller, 'Fertilisation,' p. 251, ' Weit. 

 Beob.,' I, p. 300.) — The flowers of this species belong to class Hb. Hermann Muller 

 describes the free part of the receptacle as a tube 3 mm. long, prolonged to more 

 than 5 mm. by the erect petals. Otherwise, the flower mechanism agrees with that 

 of R. rubrum. Warnstorf (Schr. natw. Ver., Wernigerode, xi, 1896) says that there 

 is slight protogyny. The style with its yellow very sticky stigma projects about 

 I mm. beyond the stamens. The pollen-grains are white, rounded three- to five- 

 sided, or shaped like an obelisk, smooth, with distinctly projecting germinating 

 papillae, 37 /x in diameter on an average. The petals are at first quite white, but 

 after fertilization they become rose-red in colour, so tl)at, as in R. aureum, the 

 inflorescence is rendered more conspicuous. 



Visitors. — Herm. Muller observed 3 bees, skg. — i. Apis mellifica 7.. ^ ; 2. 

 Itombus pratorum Z. 5 ; 3- Osmia rufa Z. 5. 



I'lateau noticed Apis and Osmia bicornis Z. in Belgium. Burkill saw Bombus 

 terrester Z. on the coast of Yorkshire ('Fertlsn. of Spring Fls.'). 



989. R. petraeum Wulf (Ricca, Atii Soc. ital. sc. nat., Milano, xiv, 1871 ; 

 Herm. Muller, ' Fertilisation,' p. 251, ' Alpenblumen,' pp. 111-12.) — The flowers of 

 this pjiecies belong to class C. Ricca describes them as slightly protogynous, 



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