302 ANGIOSPERMAE^DICOTYLEDONES 



a hinge-joint. After having been lifted up by a humble-bee probing for nectar in the 

 base of the flower, the elasticity of the hinge causes it to resume its original position, 

 once more closing the entrance of the corolla as soon as the insect leaves. A 

 proboscis must be at least i6 mm. long in order to suck all the nectar, and even then 

 the humble-bee is obliged to force its head into the upper part of the corolla-tube. 

 To obtain it conveniently a proboscis 20 mm. long is necessary. Bombus hortorum 

 L. $ (proboscis 19-21 mm.) can therefore suck easily, but the 5 of this species (prob. 

 16 mm.) with some difficulty, as Loew was able to observe in the Berlin Botanic 

 Garden. Bombus terrester L. tried in vain to lift the upper lip and reach the 

 nectar. 



Bombus hortorum L. is therefore our only native humble-bee which can suck all 

 the nectar legitimately, and, in brushing first against the stigma and then against the 

 anthers, eifect crossing. All other insects are incapable of lifting the hinged upper 

 lip. The flowers of the species are therefore monotropous , i.e. adapted solely to 

 a single kind of pollinator. 



Visitors. Loew observed 2 bees in the Berlin Botanic Garden. 

 I. Bombus hortorum L. $, raising the upper lip and skg. ; 2. B. terrester L. 5, 

 vainly trying to raise the upper lip. 



2349. P- armeniaca Willd. 



Visitors. Loew observed 3 bees in the Berlin Botanic Garden. 



I. Anthidium manicatum L. i, skg. ; 2. Bombus hortorum L. $, steadily skg. ; 

 3. Osmia aenea L. 5, skg. 



2350. P. cashmiriana Royle. 



Visitors. Loew (Berlin Botanic Garden) observed the humble-bee Bombus 

 agrorum F. $, skg. 



727. Sideritis Toum. 



2351. S. romana L. (Delpino, *Ult. ess.,* pp. 144-6.) The small, black- 

 brown corolla of this species is supported by yellow bracts, and encloses the stamens 

 and the very short style in its tube. Each of the two shorter of the four stamens 

 possesses a crescent- shaped connective, which bears a fertile anther-lobe on one side 

 and a sterile one on the other. The connectives are so placed that they form a 

 complete ring round the nectar- passage. When an insect inserts its proboscis into 

 this, it touches the pollen on the inside of the ring, and this adheres closely by means 9| 

 of viscid spherules (cf. the remark on Stachys grandiflora, p. 300). If the insect" 

 visits a second flower of this species, the pollen adhering to its proboscis will bCj 

 scraped off against the cup-shaped stigma. 



3352. S. montana L. Kerner says that the flowers of this species agree wi 

 those of S. romana. 



2353. S. hyssopifolia L. 



Visitors. The following were recorded by the observers, and for the localities 

 stated. 



MacLeod (Pyrenees), 5 humble-bees, a Lepidopterid, and a fly (Bot. Jaarb. 

 Dodonaea, Ghent, iii, 1891, p. 333). Loew (Berlin Botanic Garden), the honey-bee 

 and the humble-bee Bombus terrester Z. J, skg. 



