INFLUENCE OF THE ORIGIN OF CELLS ON FERTILISATION. 809 



there are also other contrivances of a very different nature which have the sole 

 purpose of transferring the pollen of hermaphrodite flowers, by the help of insects, 

 to the stigma of another flower of the same or of a different plant. In most 

 Orchideae, Asclepiadeae, Viola, &c., the reproductive organs of each individual flower 

 are developed at the same time, but at the time of maturity mechanical contrivances 

 exist which prevent the pollen falling on the stigma of the same flower ; it must be 

 carried by insects to other flowers. 



In other cases, as Hildebrand has shown in the case of Corydalis cava ^ the 

 pollen does actually fall on the stigma of the same flower, but is there impotent, 

 having the power of fertilising only when it falls on the stigma of a different flower, 

 and only perfecdy when carried to the flower of a different individual of the same 

 species. Such a plant is therefore only morphologically hermaphrodite, but is 

 physiologically dioecious. J. Scott states that Oncidiwn inichrochilum 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 fulgeits and Verhascum 

 nigrum, and in species of Begonia by Fritz IMiiller^. 



No less remarkable is another contrivance for the mutual fertilisation of different 

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

 consisting in a difference between different 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 all the flowers have a short style 

 and long filaments, as in Lijiiim perenne, Primula sinefisis, 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 different specimens of the 

 same species exhibit three different 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 peremie) 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, fer- 

 tihsation 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. 



^ [Ueber die Befruchtung voii Corydalis cava, Jahrb. fiir wiss. Bot. 1866,] 



2 According to Fritz Miiller (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. 



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



* [Darwin, On the Two Forms, or Dimorphic Condition, in the Species of Primula, Journ. 

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

 ibid., 1863, p. 69; ditto, On Trimorphism m 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, Journ. Lin. Soc. 1868, p. 393-— Ed.] 



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



^ [Darwin hasjgiven the name of legitimate to the union of two distinct forms, illegitimate to the 

 impregnation of long- or short-styled plants by their own form pollen.— Ed.] 



