PART III. | THE MECHANISMS OF FLOWERS. 493 
tip curls round under the superior lobes of the taller anthers; 
so that cross-fertilisation in case of insect-visits and self-fertilisation 
in their absence are insured here also, but not in the same way as 
in G@, Tetrahit. 
I have frequently observed Bombus agrorum, F. ¢ (12—15), 
sucking the honey and fertilising the flower. Some other visitors 
are enumerated in No. 590, III. 
Galeopsis versicolor, Curt.—The tube is 18 to 22 mm. long, and 
wide enough for a space of 6 to 8 mm. at its upper end to admit 
a humble-bee’s head. <A bee, if it thrusts its whole head, 5 to 6 
mm..long, into the tube, requires a proboscis 12 to 16 mm. long 
to exhaust the honey, and one at least 10 mm. long even to taste 
it, as the honey does not fill more than 2 or 3 mm. of the tube. 
Of all our humble-bees, only B. hortorwm, L, (19—21), and the 
females of B. agrorum, F. (15), B. senilis, Sm. (15), and B. fragrans, 
K. (15), can drain or nearly drain G. versicolor of its honey. 
Otherwise the flower resembles that of G. Tetrahit, save that the 
guiding-marks are much more conspicuous ; for while the flower is 
mainly yellowish-white, the under lip is dark violet anteriorly, and 
yellow at its base. I have not yet observed bees visiting the 
flower. Axell (17) found that when insects were excluded the 
plant produced seed by self-fertilisation. 
358. GALEoPsIS LADANUM, L.—The tube is 11 to 16 mm. 
long, and its wide part 5 to 6 mm. ; so that in the shortest examples 
a bee with a proboscis only 6 mm. long can drain all the honey 
if it forces its way for a distance of 5 mm. into the tube. In 
the relative positions of stigma and anthers this species exactly 
resembles G. ochroleuca. In regard to the nectary and the way 
in which the bee’s proboscis is guided towards the entrance of the 
tube, the flower agrees with that of G. Tetrahit. I have seen the 
following bees effecting fertilisation :— 
(1) Bombus agrorum, F. 9 (12—15) ; (2) B. lapidarius, L. ¢ (8—10) ; (3) 
B. silvarum, L. 2 (12—14); (4) Nomada Jacobeee, Pz. ? (6), all sucking 
normally. See also No. 590, 111., and No. 609. 
359. LAMIuM ALBUM, L.—The base of the ovary expands 
anteriorly into a fleshy lobe, which secretes honey and invests the 
two anterior divisions of the ovary for half their height (Fig. 167, 
3, a). The base of the corolla-tube, for a space of 3 to 3} mm., is 
narrow and serves to contain the honey ; it points obliquely upwards 
from the stem, and is closed above by a ring of hairs. Immediately 
