Jan. 9, 1879] 



NATURE 



215 



to the contrivances by which insects, while feeding on or 

 sucking the honey from the nectary, are ahnost compelled 

 to be the involuntary agents in the transmission of the 

 pollen from the anther to the stigma in a different flower 

 of the same species. In almost all cases, however, it is 

 only a comparatively small number of insects that would 

 be adapted, by the size of their body, the length of their 

 proboscis, and other points in their structure, to insure 

 the cross-fertilisation of any particular species of flower. 

 It is obvious that the visits of all other insects, which 

 would consume the honey without aiding in the transmis- 

 sion of pollen, not only can be of no advantage, but must 

 be positively injurious to the plant, by preventing the 

 visits of the useful insects. It is this point that Prof. 

 Kerner has studied with great industry and acumen ; and 

 he has compiled a number of most interesting illustra- 

 tions of the contrivances presented in the structure of 

 the flower, which not only force the useful insects to 

 enter it in the particular way? which shall be of most 

 advantage to it, but keep out all others. 



Dr. Kerner is dissatisfied with the vague use in botani- 

 cal works of the words " self-fertilisation " and " cross- 

 fertilisation," and proposes to substitute them by others 

 •which shall have a more definite meaning. He uses the 

 term "autogamy" for the fecundation of a flower by the 

 pollen from the andrcEcium of the same flower ; " geito- 

 nogamy" for the fecundation of a flower by pollen from 

 other flowers on the same plant ; and "xenogamy" for 

 fecimdation by the pollen from a flower on another plant ; 

 while the term "allogamy" would include the last two 

 as contrasted with autogamy. The only previous attempt 

 at a strict scientific terminology with which I am 

 acquainted is by Delpino,' who distinguishes four kinds 

 of fecundation: homoclinic homogamy, fecundation by 

 pollen from the androecium of the same hermaphrodite 

 flower; homocephahc homogamy, fecundation by pollen 

 from the androecium of a different flower of the same 

 inflorescence ; monoicous homogamy, fecundation by 

 pollen from the androecium of a flower belonging to a 

 different inflorescence on the same plant ; and dichogamy 

 fecundation by pollen from [the androecium of a flower 

 on a different plant. Prof. Kerner' s terms will at all 

 events be admitted to have the merit of being the 

 simplest, and will probably be generally adopted in 

 future. 



It may be stated as a general rule that, while the 

 visits of winged insects are beneficial, those of wingless 

 insects are mostly injurious, since these consume the 

 nectar without immediately afterwards visiting another 

 flower so as to favour allogamy. Hence the majority of the 

 contrivances which Kerner describes are for the purpose 

 of excluding from the flower wingless insects, and in 

 particular ants, the great enemies of flowers, and the 

 aphides which attract ants. The flora of the mountain 

 valleys of the Tyrol furnishes almost inexhaustible 

 material for working out a problem of this kind ; and of 

 this material Dr. Kerner, who holds the position of 

 professor of botany in the University of Innsbriick, has 

 availed himself to the full. 



Simplest among the contrivances for excluding useless, 

 while admitting useful insects, are the more or less dense 

 collections of hairs which cover up the entrance to the 



' N-ucvo Giornale Botanko Italiano, vol. viii., 1876, p. 146. 



nectary in so many flowers, rendering the road in- 

 accessible to very small insects, while presenting no 

 obstacle to larger insects which can brush them aside 

 or pierce them with their proboscis. Beautiful instances 

 of this arrangement are described and illustrated in the 

 work before us in the cases of Anchiisa arvensis, Lonicera 

 alpigetia, Veronica chamcedrys and officinalis, Malva 

 roiundifolia, Monotropa hypopitys, Menyanthes trifo- 

 liafa, and many others. Sometimes these coverings take 

 the form of appendages to the corolla which protect the 

 openings to the nectariesVith flaps, as in Gentiana nana 

 and Soldatiella alpina. Again, access to the nectary by 

 small insects is often prevented by the parts of the 

 flower being bent, dilated, or crowded together, the same 

 contrivances resulting also in forcing those insects which 

 are useful to enter and leave the flower in such a way 

 as to be of the greatest service in the transmission of 

 pollen. Thus, in Nigella each spoon-shaped petal is 

 hollowed out into a kind of pit, into which nectar is 

 secreted in abundance. At the point where the handle 

 of the spoon is continuous with the bowl the petal gives 

 off an excrescence which covers in the whole nectar- 

 cavity like a lid, closing it completely, and no insect can 

 possibly rifle the nectar unless it be strong enough to lift 

 up this lid. Ants are by this means entirely excluded^ 

 while the common honey-bee is able to lift the lid with 

 ease, in doing which he must inevitably rub against either 

 anther or stigma, according to the stage of development 

 of the flower. In his "Entdeckte Geheimniss der Natur" 

 (1793) Sprengel describes, with wonderful accuracy, the 

 proterandrous flower of Nigella, and the mode in which 

 the structure of the various parts secures allogamy by the 

 agency of bees. He observed the flaps over the nectaries, 

 but suggests no other interpretation of them than to serve 

 as a protection against rain. A similar occlusion of the 

 nectary against small insects is effected in Cynoglossum 

 by the outgrowths from the mouth of the corolla, in Cam- 

 panula and Phytemna by the strap-shaped lower parts of 

 the filaments, in Ranunculus glacialis and many Mesem- 

 br>'anthemaceae and Cactaceas |,by the mass of crowded 

 filaments, in Pentstemon by the fifth barren stamen. 



These protective and prohibitive arrangements are 

 frequently placed, not inside, but outside, the flower, 

 one very common form being the hairs, glandular or not, 

 with which the calyTc, bracts, or upper part of the stem 

 are so frequently clothed ; and the purpose is still more 

 effectively answered when the glandular hairs or the 

 stem itself exude a viscid secretion. In such plants as 

 Cisttis ladaniferus, Listera ovata. Geranium sylvaticum, 

 Euphrasia viscosa, Lychnis viscaria, and a large number 

 of species belonging to the orders Caryophyllacese, Saxi- 

 fragaceae, Labiatas, and Scrophulariaceae, it is almost 

 impossible for the flower to be visited by any but winged 

 insects. Prof. Kerner believes that the numerous insects 

 which are found adhering to the viscid peduncles and 

 stems of these plants are not digested so as to serve the 

 plant with nutriment, but that the object of their destruc- 

 tion is simply to prevent their reaching and rifling the 

 nectary. An explanation is thus offered of the well- 

 known fact that the same species will frequently assume 

 a hairy habit when growing on land, and a glabrous habit 

 when growing in water, water-plants being almost inva- 

 riably destitute of hairs. An admirable instance of this 



