86 THE FERTILISATION OF FLOWERS. [PARY III. 
In July, 1868, I assured myself of the actual certainty of cross- 
fertilisation by direct observation. I saw, in Thuringia, upon a 
field covered with wild larkspur in flower, numerous examples of 
Bombus hortorum, L. 9 and §, sucking at the flowers of this species 
with such diligence that certainly no flower in its. second period 
can have escaped being fertilised. 
Since the length of the spur is about 15 mm. from its insertion, to 
which must be added the wide entrance, 7 mm. long, a proboscis 
fully 15 mm. long is needed to suck the honey in the normal way. 
Besides Bombus hortorum, L. (17 to 21), B. agrorum, F. (10 to 
15), B. fragrans, K. (15) and B. senilis, Sm. (14 to 15), some 
species of Anthophora, viz., A. wstivalis Pz. (15), A. retusa, L. (16 
to 17), and -A. pilipes, F, (19 to 21), are all fitted for sucking the 
honey; but all must do so with greater loss of time, through 
having to force the head deep into the entrance to the spur, 
except A. pilipes, whose season is over when Delphinium comes 
into flower. Bombus hortorum seems thus to be the only species 
which is well adapted for the flower; but the diligence of 
this one species compensates the plant for the exclusion of 
all other insects. I have noticed Satyrus and species of Hesperia 
sucking at the flowers, and sinking their thin proboscides into 
the spur, but apparently they did not touch the anthers or 
stigmas. | 
Dr. Ogle gives in the Popular Science Review (631) a description 
of a species of larkspur which differs from those here described in 
that the honey secreted by the upper petals is contained in the 
spur of the posterior sepal. I unfortunately cannot determine 
which species of Delphinium is referred to as “the blue larkspur 
of our gardens,” 
Delphinium Ajacis, L., described by Sprengel, agrees in most 
points with D. Consolida, and is likewise fertilised by humble- 
bees. . 
16. AconttuM NAPELLUs, L.—This plant is distributed through- 
out the Alps, especially about the Sennerei. It has distinctly proter- 
androus flowers, which are visited by humble-bees, as Sprengel long 
ago observed. The two posterior sepals cohere to form a helmet- 
shaped structure, which shelters the anthers and nectaries; the 
two lateral sepals give foothold to the mid and hindlegs of 
humble-bees ; all four play, in addition, the part of petals, making 
the flower conspicuous by their blue colour, Of the four petals, 
the two anterior help to close in the essential organs laterally; 
