OCR Text |
Show ,!08 SEXUAL RELATIONS OF PLANTS. UJIAP. X. ane1nophilous. A· plant would bo neglected by insects if nectar failed to be secreted, unless indeed a large supply of attractive pollen was present; and from what we have seen of the excretion of saccharine fluid from leaves and glands being largely governed in several cases by climatic influences, and froin some few flowers which do not now secrete neetar still retaining coloured guiding-marks, the failur-e of the secretion cannot be considered as a very improbable event. The same result would follow to a certainty, if winged insects ceased to exist in any district, or became very rare. Now there is only a single plant in the great order of the Oruciferm, namely, Pringlea, which is anemophilous, and lhis plant is an inhabitant of Kerguelen Land,* where there are hardly any winged insects, owing probably, as was suggested by me in tho case of Madeira, to the risk which they run of being blown out to sea and destroyed. A remarkable fact with respect to anemophilous plants is that they are often diclinous, that is, they are either moncecious with their sexes separated on the same plant, or dicecious with their sexes on distinct plants. In the class Moncecia of Linnmus, Delpino shows t that the species of twenty-eight genera are anemophilous, and of seventeen genera entomophilous. In the class Dioocia, the species of ten genera are anemophilous and of nineteen entomophilous. The larger proportion of entomophilous genera in this latter class is probably the indirect result of insects having the power of carrying pollen to another and sometimes distant plant much more securely than the * The Rev. A. E. Eaton in 'Proc. Royal Soo.' vol. xxiii. 1875, p. 351. . t ' Studi sopra un Lignaggio anemo:filo delle Compositro,' 1871. CHAP. x. SEXUAL RELATIONS OF rJ_jANTS. 409 wind. In the above two classes taken too-ether thor are t~irty-eight anemophilous and thir~y-six entomophilous ~enora; whereas in the great mass of hermaphrodite plants the proportion of anemophilous to entomophilous genera is extremely small. The cause of this remarkable difference may be attributed to anemophilous plants having retained in a greater degree than the entomophilous a primordial condi· tion, in which the sexes were separated and their mutual fertilisation effected by means of the wind. That the earliest and lowest members of the vegetable kingdom had their sexes separated, as is still the case to a large extent, is the opinion of a high authority, Nageli.* It is indeed difficult to avoid this conclusion, if we admit the view, which seems highly probable, that the conjugation of the Algm and of some of the simplest animals is the first step towards sexual reproduction ; and if we further bear in mind that a greater and greater degree of differentiation between the cells which conjugate can be traced, thus leading apparently to the development of the two sexual forms.t \Ve have also seen that as plants became more highly developed and affixed to the ground, they would be compelled to be anemophilous in order to intercross. Therefore all plants which have not since been greatly modified, would tend still to be both diclinous and anemophilous ; and we can thus understand the connexion between these two states, although they appear at first sight quite ----- ~ • 'Entstehung und BeoTiff der naturhist. Art,' 1865, p. 2°2. . t See the interesting discus· ti?,n on. ~his :vhole subject by 0. Butschh m h1s ' Studien tiber die er.sten Entwickelungsvorgange der E1Zelle,' &c. 1876, pp. 207-219. Also, Engelmann, "Ueber Entwickelung von Infuso rien," 'M01·· pl1ol. Jahrbuch,' B. i. p . .573. Also, Dr·. A. Dodel, "Die Kraushaar- Alge," 'Pringsheims Jahrb. f. wiss. Bot.' B. x. |