[323]

Oxalis Valdiviana

June 19' 1878.

[figure pasted on]

Oxalis Valdiviana June 19th Fig. 13. z D

1/2 scale to be lettered

(must be recopied)

Conjoint Circumnutation of cotyledon & hypocty traced on vertical glass Seedling illuminate from above.) Reduce to 1/2 origin Scale

[324]

34 645

Chap. E 10

are excluded, about 32 have flowers which are asymmetrical or present some remarkable peculiarity; whilst in the second list og genera which were more or less fertile genera where insects were excluded about about 21 out of the 47 are thus characterised. à (open)

Means of cross-fertilisation. ─ The most important of all the agents by which pollen is carried from flower to flower are insects, belonging to the orders of Hymenoptera, Lepidoptera; and in some parts of the world, birds.* Next in importance, but in a quite subordinate degree, is the wind; and with some aquatic plants, according to Delpino, currents of the water. The simple fact of the necessity of such extraneous aid, and the many contrivances for the purpose, considered by themselves, renders it highly probable that some great benefit must be is thus gained; and this conclusion has now been firmly established by the proved superiority in growth, vigour and fertility of plants─ of crossed parentage over those of self-fertilised parentage plants. But we should always keep in mind that two some=

[Cross and self fertilisation, pp. 370-72: "Thus out of the forty-nine genera in the first list, about thirty-two have flowers which are asymmetrical or present some remarkable peculiarity; whilst in the second list, including species which are fully or moderately fertile when insects were excluded, only about twenty-one out of the forty-nine are asymmetrical or present any remarkable peculiarity.
Means of cross-fertilisation.—The most important of all the means by which pollen is carried from the anthers to the stigma of the same flower, or from flower to flower, are insects, belonging to the orders of Hymenoptera, Lepidoptera, and Diptera; and in some parts of the world, birds.* Long-beaked humming-birds visit the flowers of Brugmansia, whilst some of the short-beaked species often penetrate its large corolla in order to obtain the nectar in an illegitimate manner, in the same manner as do bees in all parts of the world. It appears, indeed, that the beaks of humming-birds are specially adapted to the various kinds of flowers which they visit: on the Cordillera they suck the Salviae, and lacerate the flowers of the Tacsoniae; in Nicaragua, Mr. Belt saw them sucking the flowers of Marcgravia and Erythina, and thus they carried pollen from flower to flower. In North America they are said to frequent the flowers of Impatiens: (Gould 'Introduction to the Trochilidae' 1861 pages 15, 120; 'Gardeners' Chronicle' 1869 page 389; 'The Naturalist in Nicaragua' page 129; 'Journal of the Linnean Society Botany' volume xiii. 1872 page 151.) I may add that I often saw in Chile a Mimus with its head yellow with pollen from, as I believe, a Cassia. I have been assured that at the Cape of Good Hope, Strelitzia is fertilised by the Nectarinidae. There can hardly be a doubt that many Australian flowers are fertilised by the many honey-sucking birds of that country. Mr. Wallace remarks (address to the Biological Section, British Association 1876) that he has "often observed the beaks and faces of the brush-tongued lories of the Moluccas covered with pollen." In New Zealand, many specimens of the Anthornis melanura had their heads coloured with pollen from the flowers of an endemic species of Fuchsia (Potts, 'Transactions of the New Zealand Institute' volume iii. 1870 page 72.) Next in importance, but in a quite subordinate degree, is the wind; and with some aquatic plants, according to Delpino, currents of water. The simple fact of the necessity in many cases of extraneous aid for the transport of the pollen, and the many contrivances for this purpose, render it highly probable that some great benefit is thus gained; and this conclusion has now been firmly established by the proved superiority in growth, vigour, and fertility of plants of crossed parentage over those of self-fertilised parentage. But we should always keep in mind that two somewhat opposed ends have to be gained; the first and more important one being the production of seeds by any means, and the second, cross-fertilisation.
* I will here give all the cases known to me of birds fertilising flowers. In South Brazil, humming-birds certainly fertilise the various species of Abutilon, which are sterile without their aid (Fritz Müller 'Jenaische Zeitschrift f. Naturwiss.' B. vii. 1872 page 24."]