Sept. 24, 1 8 74 J 



NATURE 



425 



ing a pistil and two groups of stamens), which he calls, from the 

 relative lengths of their pistils, the long-styled, mid-styled, and 

 short-styled. In this species, also, it is remarkable that the 

 seeds of the three forms differ from one another, loa of tlie long- 

 styled seeds being equal to 121 mid-styled or i42sIiort-styled. The 

 pollen grains also not only differ in size (the long stamens having 

 the largest-sized pollen grains, the middle-sized stamens middle- 

 sized pollen grains, and the short stamens small pollen grains), 

 but also in colour, being green in the longer stamens, and yellow 

 in the shorter ones ; wliile the filaments are pink in the long 

 stamens, uncoloured in the shorter ones. Mr. Darwin has also 

 ]iroved by experiment that this species does not set its seeds, if 

 the visits of insects ares prevented ; in a state of nature, how- 

 ever, tlie plant is much frequented by bees, humble-bees, and 

 flies, which always alight on the upper side of the flowers in the 

 stamens and pistil. 



He has also shown that in this species, as in Primula, perfect 

 fertility can only be obtained by fertilising each form with pollen 

 from stamens of corresponding length. This case is indeed most 

 complex, as the pollen of each set of stamens, when applied to 

 the same stigma, acts most differently, and it would appear that 

 the greater the inequality in length between the pistil and 

 stamens, the greater the sterility. 



The genus Lythrum is also remarkable for the great differences 

 existing between different species. L. grefferi, like L. salicaria, 

 is trimorphic ; vvhde L. Ihyndjolia is dimorphic ; and L. hysso- 

 tijt^lid is homomorphic. 



Let us consider the manner in which the bees are adapted to 

 the flowers. Although we may ui one respect say that the gene- 

 ral organisation of the insect is modified with reference to these 



Fig. 32. 



Fig. 33. 



relations, still, as Midler, from whom the following facts are 

 mainly taken, has well shown, the parts wliich have been the 

 most profoundly modified are the mouth and the legs. If we 

 are asked why we assume that in this case the mouth-parts and 

 legs have been modified, the answer is that tliey depart greatly 

 from the type found in allied insects, and that between this tyjie 

 and these modified examples various gradations are to be found. 



The mouth* fflr an insect, say of a wasp (Fig. 23), is composed 

 of (i) an upper hp, 17, (2) an underlip, d, {3) a pair of anterior 

 jaws or mandibles, /', and (4) apair of posterior jaws or maxillae, c. 

 These two pairs of jaws work laterally, that is to say, from side 

 to side, and not as in man and other mammalia, from above to 

 below. The lower lip and maxilla; are each provided with a 

 pair of feelers or palpi [c and J, .1). The above figures repre- 

 sent the mouth-parts of a wasp, in which, as is very usually the 

 case, the mandibles are hard and horny, while the maxilla; are 

 more deUcate and membranous. In the different groups of insects 

 these organs present, however, almost infinite variations. 



rig. 24 represents the mouth-parts of a bee, Trosopis (Fig. 25). 

 The bees belonging to this genus construct their cells in sand, or 

 in dry bramble sticks, lining them with a transparent mucus, 

 which they smooth down with their trowel-like lower lip 

 and which hardens into a thin membrane. That the mouth 

 of Prosopis probably represents the condition of that of the an- 

 cestors of the hi\e-bees before their mouthparts underwent 

 special modifications, may be inferred from the fact that the 

 same type occurs in other allied groups, as is shown in Fig. 26, 

 which represents the mouth of a wasp (Polistes), also seen from 

 below. 



We may therefore consider that Prosopis shows us special 

 adaptation for the acquirement of honey, and in fact though the 

 bees belonging to this genus feed their young on honey and 

 pollen, they can only get the former from those flowers in which 



it is on the surface. In Andrena (Fig. 27), Halictus (Fig. 28), 

 Panurgus (Fig. 29), Halictoides (Fig. 30), and Chelostoma (Fig. 

 31), we see various stages in the elongation of the lower lip until 

 at length it reaches the remarlcable and extreme form which it 

 now presents in the hive- and humble-bees, and which enable 

 them to extract the honey from most of our wild flowers, though 

 no bees have the proboscis so much elongated as is the case with 

 some butterflies and moths ; perhaps as Hermann Midler has 



''"II.::'' I ^S'"'^ 



Fig. 35. 



Fig. 36. 



suggested, because the necessity of using their mouths for certain 

 domestic purposes has Hmited its specialisation in this particular 

 direction. 



There are several flowers which are inaccessible to hive-bees, 

 and to Bonibus L-rnslris, which has a shorter proboscis than 

 some of the other species belonging to that genus. Hermann 

 MiiUer mentions, for instance, that he has often seen Boinlnts 

 tcmstrh endeavouring, in vain, to suck the flowers of the Oxhp 

 {Pyiiiuda dalior). Having satisfied themselves that they were 

 unable to do so, but not till then, they proceeded to cut a hole in 

 the base of the tube, and thus arrived at the honey. This seems 

 to show, he obsei-ves, that they act upon the results of expe- 

 rience, and not by what is called mere instinct. Indeed any one 

 who has watched bees in greenhouses will see that they are 

 neither confined by original instinct to special flowers, nor do 

 they visit all flowers indifferently. MiiUer mentions several cases 

 in which he has seen honeyless flowers visited by insects ; 

 Genista tinctona, for instance, is frequently visited by insects in 

 search of honey although it does not contain any. 



Certain insects, on the other hand, confine themselves to par- 

 ticular flowers. Thus, according to II. MiiUer, 

 Andixna floral visits exclusively Bryonia dioica, 



Blalictoidcs ,, ,, species of Cainpannla, 



Andrena hattorfiana „ ,, Scaiiosa arrensis, 



Cilissa melanara ,, „ Lylterum salicaria, 



Macropis lal'iata ,, ,, Lysiinachia vulgaris, 



Osmia aduma „ „ Echiitm. 



Fig. 37. 



It would also appear that individual bees differ somewhat in 

 their mode of treating flowers. Some humble bees suck the 

 honey of the French Bean and the Scarlet Runner in the legiti- 

 mate manner, while others cut a hole in the tube and thus reach 

 it surreptitiously ; and Dr. Ogle has observed that when he 

 followed any particular bee she always proceeded in the same 

 manner ; some always entering by the mouth, others always 

 cutting a hole. He particularly mentions that this was the case 

 with bees of one and the same species, and infers, therefore, that 



