Mabch 1, 1895.] 



KNOWLEDGE 



61 



therefore, compensate for their lack of diligence. The 

 visit of a systematic worker is far more efficient than that 

 of a less industrious insect ; but this is due quite as much 

 to intelligence as to diligence, for the careless or un- 

 intelhgent can no more avoid entering the same flowers 

 repeatedly than a number of separate insects working 

 independently. Kevisitation not only does a flower no 

 good, but involves loss, its poUen being brought back and 

 applied to its own stigma instead of being transferred 

 to another blossom. Insects which return to flowers 

 already \asited lose their time. In their own interest, 

 therefore, the more intelligent will avoid overlapping, and 

 their efficiency as fertilizers wiU increase in proportion. 



From the structure of the honeycomb, which afi'ords a 

 maximum of storage capacity with a minimum expenditure 

 of wax and labour, we are prepared for a corresponding 

 economy in the work of collecting honey. The methods 

 adopted by the bee for the purpose of saving time are 

 interesting and instructive in a high degree. Intelligent 

 procedure is essential in view of the extremely small 

 amount of nectar contained in most flowers. By chemical 

 analysis the quantity of sugar present in any blossom can 

 easily be ascertained. Some years ago I made a number 

 of experiments which illustrate the arduous nature of the 

 task performed by bees. The results showed that to 

 obtain one grain of sugar a considerable number of flowers 

 are requisite. Of the blossoms of the fuchsia Si, of the 

 sweet pea 6j, of the monk's-hood 10j\y, and of the red 

 clover 8^^ heads were respectively needed to furnish a 

 single grain of sugar. Of smaller blossoms a much larger 

 number was necessary. In the clover, which may be taken 

 as a typical example, the head consists of about sixty 

 florets, and we must, therefore, multiply the 8j by this 

 number to find how many times the insect's proboscis 

 must be inserted into a flower to obtain a grain of sugar. 

 There are 7000 grains in a pound; this quantity, there- 

 fore, represents 8j x 60 x 7000, or 3, -165, 000 separate 

 flowers. Honey, however, only contains about seventy- 

 five per cent, of sugar, so that in round numbers a pound 

 of honey represents two and a half millions of clover tubes 

 rifled by the bees ! 



It is evident from this illustration that industrious 

 habits are indispensable to insects which depend on 

 sugar as a source of sustenance, and it is not surprising 

 that they should try to lighten their labours by economical 

 methods. A more remarkable chcumstance is that the 

 arrangements in many flowers are specially adapted to 

 turn these economical habits to advantage in promoting 

 cross-fertilization. 



The first of these methods of saving time worth mention- 

 ing was noticed by Aristotle, and may be observed by 

 anyone who cares to follow the operations of a bee. A 

 marked characteristic of the bee's method of working is, 

 that in the course of a single journey the insect, as a rule, 

 confines its visits to the flowers of one species of plant. 

 The Lepidoptera and some of the Diptera also follow this 

 method, though not, perhaps, so rigidly as bees. Mr. A. W. 

 Bennet, who has paid some attention to the methodic habits 

 of insects in visiting flowers, records three flights of the 

 painted lady, in which the insect confined itself to the 

 same species, settling six, three, and ten times respectively. 

 A hive-bee paid nine successive visits to the same species 

 of flower ; one bumble-bee fifteen, and another eleven, 

 passing over many other flowers. Mr. H. 0. Forbes saw 

 a bee visit thirty llowers of the dead nettle in succession, 

 passing over other flowers, such as Convolvulus, Eubus 

 and Solanum. This habit is very manifest, particularly 

 in our native bees ; when any plant is very abundant they 

 may frequently be seen at work upon its blossoms almost 



continuously, for hours, if not for entire days. No doubt 

 this is partly explained by the limited number of species 

 whose flowers secrete nectar on any given day. A flower 

 does not generally begin secreting until its essential 

 organs are mature, since the need for economy presses 

 upon the blossom as well as the bee. There can be no 

 doubt, however, that Mr. Darwin's explanation is the true 

 one. By keeping to one kind of flower at a time the insect 

 gets familiar with its ins and outs, and can thus work more 

 rapidly, while practice makes it expert, and thus time and 

 labour are saved. 



The importance of this habit to flowers is very obvious. 

 An insect which visits all kinds of flowers indiscriminately 

 misplaces the pollen, carrying it to the stigmas of a 

 different species from that whence it was obtained. Con- 

 stancy on the part of the visitor prevents the pollen being 

 taken to the wrong flowers, where it would be quite wasted. 

 Not only, therefore, must an insect profit by its abihty to 

 recognize diflerent flowers quickly, but the flowers themselves 

 benefit by possessing distinctive marks whereby the species 

 may be easily distinguished. One reason for the diversity 

 of colour, scent and form met with in flowers is doubtless 

 to foster this habit of constancy. Flowers specialized for 

 bees in particular exhibit great variety. The odours of 

 flowers are also distinctive and highly characteristic, 

 while marks on their petals usually serve as honey-guides ; 

 but the bright spots on London pride and other Saxifraga, 

 and the tesselated draught-board pattern of the crown 

 imperial, cannot be of much use in this way. Possibly 

 their function is to aid the winged botanists in identifying 

 the species. 



The value of an insect's visit may be diminished, not 

 merely by the transference of the pollen to flowers of 

 another species, but also by its application to the stigmas 

 of flowers growing on the same plant. Insects whose 

 methodical instincts lead to the intercrossing of distinct 

 plants are preferable to those which bring about the inter- 

 crossing of flowers growing on the same plant. A bee 

 visiting a spike or raceme of flowers almost invariably 

 enters the lowest flower first, and proceeds to the others in 

 regular succession upwards. I directed the attention of Mr. 

 Darwin to this subject, and he mentioned in a letter I 

 had from him that he had observed bees visiting Tritoma in 

 this way. Tritoma, better known as the red-hot poker, is 

 a garden plant belonging to LUiaeefe ; its inflorescence is 

 an elongated spike, consisting of hundreds of tubular flowers. 

 Tritoma is adapted to Lepidoptera. Bees must have 

 difficulty in reaching the nectar, and I have not had an 

 opportunity of observing them at work on its blossoms. 

 On one occasion I saw a tomtit biting holes in these 

 flowers to get their nectar ; but although birds rarely do 

 this, humble-bees regiflarly perforate the corollas of the 

 heath and other blossoms. Quicker access is thus obtained 

 to the honey, and the insect can remove it from flower 

 tubes too deep for its proboscis. Hive-bees, when they can, 

 make use of the holes made by the humble-bee in preference 

 to entering by the mouth of the flower. The ascending 

 habit appears, however, to be common alike to the hive- 

 bee and the wild species. For a time I was at a loss to 

 account for this order of visitation, but the action of the 

 insects themselves suggested the explanation. I noticed 

 that they rarely went up the whole length of a spike, and 

 sometimes only entered one or two of its lowest flowers. 

 It then occurred to me that as the lowest flowers were also 

 the oldest and most advanced, they were more likely to 

 contain nectar than the younger ones higher up the spike. 

 An additional hint was afl'orded by Jlr. Darwin's observa- 

 tion that, on visiting a flower with several nectaries, a bee, 

 if it finds one of them empty, does not stay to examine the 



