INFLUENCE OF THE ORIGIN OF THE CELLS ON FERTILISATION, goj 



physiologically dioecious. J. Scott states that Oncidium microchilum exhibits the 

 same phenomena, the pollen not being potent on the stigma of the same flower 

 while cross-pollination ensures fertilisation^; the pollen and stigma are therefore 

 without function except to the stigma and pollen of a different flower. Similar phe- 

 nomena have been described by Gartner in the case of Lobelia fulgens and Verbascum 

 nigrum^ and in species of Bego?iia by Fritz Miiller^. 



No less remarkable is another contrivance for the mutual fertilisation of diff"erent 

 individuals of plants with hermaphrodite flowers, — Dimorphism^ (or Heterostylism), 

 consisting in a diff'erence between diff"erent individuals of the same species with 

 reference to their reproductive organs. In one individual the flowers all have a long 

 style and short filaments, while in another individual aU the flowers have a short style 

 and long filaments, as in Linum perenne, Primula sinensis, and other species of 

 Primula. It sometimes happens also, as in Lythrum Salicaria and many species of 

 Oxalis^, that the reproductive organs in the flowers of diff'erent specimens of the 

 same species exhibit three diff'erent relative lengths {Trimorphism), there being an 

 intermediate length of style between the long-styled and the short-styled forms. In 

 these cases of dimorphism and trimorphism Darwin and Hildebrand have shown that 

 fertilisation is possible only (in the case of Linum perenne") or at least has the best 

 result when the pollen of the long-styled flower is carried to the short-styled stigma 

 of another plant, and vice versa ^. Where there are three different lengths of style, 

 fertilisation succeeds best when the pollen is carried to the stigma which stands at the 

 same height in another flower as the anthers from which the pollen came. It will be 

 seen that this is but an expansion of the same rule. 



While in the very numerous diclinous, dichogamous, dimorphic, and trimorphic 

 flowers, insects carry pollen from one flower to another, it is comparatively rare for 

 cross-pollination to take place without the help of insects. This occurs in some 

 Urticacese, as Pilea and Broussonetia, where the anthers emerge suddenly from the 

 bud and scatter their light pollen in the air like a fine cloud of dust, which is then 

 blown to the female organs of other flowers. In the Rye the arrangement is still 

 simpler ; the flowers open separately, usually in the morning ; the filaments elongate 

 rapidly and push the ripe anthers out of the pales; the anthers then hang down at 

 the end of the long filaments, open, and allow the heavy pollen to fall down, thus 

 reaching the stigmas of other flowers lower down in the same spike or in neigh- 

 bouring spikes, being assisted in this by the oscillations of the haulm under the 

 influence of the wind**. 



^ According to Fritz MiiUer (Bot. Zeit. 1868, p. 114), in some species of Oncidium the pollen- 

 masses and stigmas of the same individual have a positively poisonous effect on one another. 



2 Fritz Miiller, Bot. Zeit. 1864, p. 629. 



3 [Darwin, On the Tvt^o Forms, or Dimorphic Condition, in the Species of Primula, Journ. 

 Proc. Linn. Soc. Bot. 1862, p. 77 ; ditto, On the Existence of Tv^o Forms, &c. of the Genus Linum, 

 ibid., 1863, p. 69; ditto, On Trimorphism in Lythrum Salicaria, ibid., 1864, p. 169; ditto, On the 

 Character and Hybrid-like Nature of the Offspring from the Illegitimate Unions of Dimorphic and 

 Trimorphic Plants, Joum. Linn. Soc. 1868, p. 393; ditto, The Different Forms of Flowers on Plants 

 of the same Species, 1877.] 



* Hildebrand, Bot. Zeit. 1871, Nos. 25, 26. 



^ [DarMnn has given the name oi legitimate to the union of two distinct forms, illegitimate to the 

 fertilisation of long- or short-styled plants by pollen from flowers of their own form.] 



^ [For a detailed account of the very remarkable phenomena connected with the pollination of 



