342 ANGIOSPERMAE—DICOTYLEDONES 



240. Cassia L. 



816. C. marylandica L. — In this species the anthers do not dehisce, but 

 remain covered by a thin membrane, which is ruptured by humble-bees (Nature, 

 London, xxxv, i886). 



XXXIV. ORDER ROSACEAE JUSS. 

 (Including Drupaceae DC. ( = Amygdalaceae Juss.) and Pomaceae Lindl.) 



Literature. — Hermann Miiller, 'Fertilisation,' pp. 221-43; Knuth, ' Bl. u. 

 Insekt. a. d. nordfr. Ins.,' pp. 65-6, ' Grundriss d. Blutenbiol.,' pp. 51-2. 



In this order the flowers are made conspicuous in very different ways in the 

 various genera : there are numerous transitions from the insignificant little blossoms 

 of Alchemilia to the large ones of roses, which are conspicuous from a distance. 

 The inflorescences are equally varied, even in the species of the same genus : 

 sometimes the flowers are solitary or in pairs (species of Mespilus, Cydonia, Dryas, 

 Geum, Rosa, and so forth) ; sometimes they are aggregated into more or less 

 copiously branched inflorescences — cymes, capitula, racemes, umbels, or panicles 

 (Spiraea, Crataegus, Pyrus, Sorbus, Alchemilia, Sanguisorba, Amygdalus, Prunus, 

 Potentilla, Agrimonia, and so on). Many secrete nectar from an annular ridge 

 on the inner surface of the receptacle. The quantity varies greatly : from large drops 

 (e. g. in species of Rubus and in Geum rivale), to a scarcely perceptible layer, which, 

 however, is eagerly licked by insects (Alchemilia and Potentilla) ; and there are 

 also intermediate stages. Some species are quite nectarless, others are even anemo- 

 philous. Our native forms, therefore, belong to the following flower classes. — 



An : Sanguisorba minor. 



Po : Rosa, Ulmaria, Aruncus, Kerria. 



E : Alchemilia, Sibbaldia, Amelanchier vulgaris. 



EC: Amygdalus, Prunus, Geum, Potentilla, Spiraea, Crataegus. 



C : Rubus, Comarus, Sorbus, Fragaria, Persica. 

 It follows from what has been said that the visitors of the various species are 

 very diverse. Flies, especially hover-flies, and short-tongued bees (Andrena, 

 Halictus), are commonest, while the more conspicuous flowers, and those rich in 

 nectar, are also visited by long-tongued bees, as well as beetles and even Lepido- 

 ptera. Cross-pollination by insects is frequently favoured or secured by protogyny 

 (Prunus, Amygdalus, species of Spiraea, Geum, Fragaria, Crataegus, Sorbus, and 

 Pyrus), by divergence of the stamens from the stigma in homogamous flowers 

 (species of Persica, Prunus, Rosa, and Potentilla), rarely by protandry (Rubus 

 caesius), or partial dicliny (Sanguisorba minor). Automatic self-pollination appears 

 regularly to take place in hermaphrodite flowers should insect-visits fail. 



241. Amygdalus L. 



Flowers protogynous, bright rose-red or white in colour, with half-concealed 

 nectar secreted in the lower part of the cup-shaped receptacle. 



817. A. communis L. ( = Prunus Amygdalus 5M'm).— Kirchner ('Flora v. 

 Stuttgart,' pp. 460-1) says that in this species nectar is secreted by the yellow inner 



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