732 < General Notes. [October, 
appears that the nectar of these flowers is perfectly accessible 
only to insects whose slender and flexible suctorial mouth-parts - 
reach a length of not less than 10 mm.; and these insects must 
be habituated to hanging upon flowers while probing them for 
their sweets. These requirements are met with only in certain 
humble bees. Sprengel records the flowers as being visited for 
their nectar normally, and fertilized, by large humble bees. Dr. 
üller, from observations extending over a number of years, 
finds two species of Bombus which act in this way ; the first, B. 
hortorum, has a tongue reaching a length of from 19-21 mm.; the 
second, B. agrorum, has a tongue varying from 12-15 mm. in 
length. When collecting nectar, one of these bees hangs upon 
the flowers with its prothoracic legs on the base of a spur, the 
mesothoracic and metathoracic limbs clinging to the column 
formed of the stamens and pistils. Inserting its head as far as 
possible into the flaring mouth of the nectary, it passes its tongue 
into the spur, the curve of which is readily followed when, the 
insect occupies this position, in which the ventral surface of its 
body is brought in contact with the essential organs. But the 
flowers are proterandrous, the anthers only being mature in young 
flowers, while they are replaced by the receptive stigmas in older 
ones; so the bees, going from plant to plant, constantly cross 
older flowers with pollen from those which are younger, and, 
from their habit of visiting the lower (and older) flowers of a plant 
first, they usually cross the flowers of distinct plants. Where 
the nectar has been removed from flowers, the bees soon learn to 
probe only a single spur, and finding this empty, seem to reason 
that it would be a useless waste of time to try the others, and 
hasten on to another flower. Many years ago Necker proved the 
value of these nectaries for the fruiting of the flower, for he found 
that no fruit was set after their removal; but he does not seem to 
have arrived at the correct explanation of the result of his experi- 
ment. 
Concerning the perforation of the spurs of the corolla, Spren- 
gel tells us that he found hive bees (? Bienen) on the flowers, which 
first collected pollen, then betook themselves to the bend in the 
spurs, which they bit through, thus readily obtaining the nectar. 
Dr. Müller found two small wild bees—species of Halictus—col- 
_ lecting pollen from the open anthers, but they showed no tenden- 
cy tain nectar, and hive bees trying, failed. He found, how- 
ever, that an humble bee ( Bombus terrestris), having a tongue not 
exceeding 9 mm. in length, and therefore debarred from partaking _ 
of the sweets with its more fortunate relatives, seemed to learn — 
by individual experience the futility of attempting ‘to reach the 
nectar in the normal way, afterwards acquiring the habit of 
Acta Academie Theodoro Palatinæ, v (fide Senebier). Soyer-Willemet also 
observed the same fact, and advances it on p. 13 of his “ Mémoire sur le Nectaire 
in support of his theory that nectar played a direct rôle in the act of fecundation. 
