[27]

Desmodium Gyrans

671

Chap E 10

-fertilised flowers; and thus was likewise the case to a certain extent with Vandellia. As therefore no plant which formerly at one time bore small and inconspicuous flowers had [word covered] its flowers of themrendered cleistogene, I must believe  [word covered] these plants being small & inconspicuous flowers profit by their flowers still remaining [word covered] was & being occasionally intercrossed by insects. It [has] been one of the greatest oversights in my work that I did not experimentise on such flowers; I did not do so owing to the greatest difficulty of fertilizing them, and to my not having been seen the importance of the subject.* (2) not yet [compared]

It should be remembered that in two of the cases in which highly self-fertile varieties appeared amongst my experimental plants, namely with Mimulus and Nicotiana, such varieties were greatly benefitted by a cross with a fresh stock or with a slightly different variety and this likewise was the case with the cultivated varieties of Pisum sativum and Lathyrus odoratus which have been long propagated by self-fertilisation. Therefore

[Cross and self fertilisation, pp. 387-9: "We have also seen that the seedlings of Ononis minutissima, raised from the perfect flowers fertilised with pollen from another plant, were finer than those from self-fertilised flowers; and this was likewise the case to a certain extent with Vandellia. As therefore no species which at one time bore small and inconspicuous flowers has had all its flowers rendered cleistogene, I must believe that plants now bearing small and inconspicuous flowers profit by their still remaining open, so as to be occasionally intercrossed by insects. It has been one of the greatest oversights in my work that I did not experimentise on such flowers, owing to the difficulty of fertilising them, and to my not having seen the importance of the subject.*

* Some of the species of Solanum would be good ones for such experiments, for they are said by H. Müller ('Befruchtung' page 434) to be unattractive to insects from not secreting nectar, not producing much pollen, and not being very conspicuous. Hence probably it is that, according to Verlot ('Production des Variétiés' 1865 page 72), the varieties of "les aubergines et les tomates" (species of Solanum) do not intercross when they are cultivated near together; but it should be remembered that these are not endemic species. On the other hand, the flowers of the common potato (S. tuberosum), though they do not secrete nectar Kurr 'Bedeutung der Nektarien' 1833 page 40, yet cannot be considered as inconspicuous, and they are sometimes visited by Diptera (Müller), and, as I have

It should be remembered that in two of the cases in which highly self-fertile varieties appeared amongst my experimental plants, namely, with Mimulus and Nicotiana, such varieties were greatly benefited by a cross with a fresh stock or with a slightly different variety; and this likewise was the case with the cultivated varieties of Pisum sativum and Lathyrus odoratus, which have been long propagated by self-fertilisation. Therefore until the contrary is distinctly proved, I must believe that as a general rule small and inconspicuous flowers are occasionally intercrossed by insects; and that after long-continued self-fertilisation, if they are crossed with pollen brought from a plant growing under somewhat different conditions, or descended from one thus growing, their offspring would profit greatly. It cannot be admitted, under our present state of knowledge, that self-fertilisation continued during many successive generations is ever the most beneficial method of reproduction.

The Means which favour or ensure Flowers being fertilised with Pollen from a distinct Plant.—We have seen in four cases that seedlings raised from a cross between flowers on the same plant, even on plants appearing distinct from having been propagated by stolons or cuttings, were not superior to seedlings from self-fertilised flowers; and in a fifth case (Digitalis) superior only in a slight degree. Therefore we might expect that with plants growing in a state of nature a cross between the flowers on distinct individuals, and not merely between the flowers on the same plant, would generally seen, by humble-bees. Tinzmann (as quoted in 'Gardeners' Chronicle' 1846 page 183, found that some of the varieties did not bear seed when fertilised with pollen from the same variety, but were fertile with that from another variety.

or often be effected by some means."]