238 



ANGIOSPERMAEDICOTYLEDONES 



on their backs by striking against the downwardly directed points of the pollen- 

 receptacle. They transfer this to the curved, projecting stigma of another flower. 

 Premature dispersal of pollen is prevented by the hairs which frequently surround 

 the anther-processes. 



685. Acanthus Toum. 



Literature. E. E. Haare, Natur und Haus, vi, pp. 183-4. 



Protandrous humble-bee flowers, with the reduced upper lip replaced by the 

 upper sepal, which covers the entire flower. Loew states that the nectary, situated at 

 the base of the ovary, sheds its secretion into a protrusion at the bottom of the flower, 

 which serves as a nectar receptacle, and is protected by hairs. 



2200. A. spinosus L. (Delpino, ' Ult. oss.,' p. 33 ; Kerner, Nat. Hist. PI.,' 

 Eng. Ed. I, II, p. 273; Knuth, ' Bloemenbiol. Bijdragen.') In the flowers of this 



species a convenient alighting-plat- 

 form is formed by the large, trilobed 

 lower lip; this is supported by the 

 posterior sepal, which resembles an 

 upper lip. The filaments are strong, 

 curved rods, that can only be separ- 

 ated by large and powerful humble- 

 bees. When this takes place, the 

 pollen receptacle is opened, and the 

 bees are sprinkled with pollen. 

 Each anther possesses a single 

 loculus, resembling a long, narrow 

 niche, each side of which is fringed 

 with hairs. The pollen receptacle 

 is thus kept firmly closed. The 

 style at first lies close to the roof 

 of the flower, but bends downwards 

 later on, bringing the stigma into 

 the direct line of approach to the 

 nectar. 



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

 stated. 



Knuth (Kiel Botanic Garden), 2 humble-bees (Bombus terrester Z. j, and 

 B. hortorum L. 5), which crept under the sepal functioning as an upper Hp, and 

 remained skg. nectar for some time ; also the earwig Forficula auricularia Z., dvg. 

 the flowers. Delpino, 2 humble-bees Bombus italicus F., and B. terrester Z. 



2201. A. mollis L., and 2202. A. longifolius Poir. Kerner states that the 

 flower mechanism of these two species agrees with that of A. spinosus. 



Visitors. Delpino observed the same 2 humble-bees as for A. spinosus. 



Fig. 344. Acanthus s/>itu>sus, L. (from nature). A. 

 Flower in the first (male) stage, seen from above after re- 

 moval of the upper protective sepal and the reduced upper 

 lip. B. Do., in the second (hermaphrodite) stage, seen 



from below after removal of the lower lip. a, anthers ; 



, nectary ; j, stigma. 



