170 THE STRUCTURE OF FLOWERS. 



The exciting effect of the tubes is seen when Orchids are 

 crossed which have no affinity, and are therefore incapable 

 of fertilisation. Thus, the pollination of Orchis mascula by 

 Gypripedium paviflorum even determined the formation of 

 the sexual ap23aratus in the former. Similarly, when Orchis 

 and Listera, as well as Ophrys and Limodorum were crossed, 

 ovules reaching various degrees of development were pro- 

 duced, but none were impregnated. 



Everything indicates (writes M. Guignard) that the 

 development of the ovules is subordinated to that of the 

 ovary. In exotic Orchids the thickness of this organ and its 

 elongation are often very pronounced before the appearance 

 of the ovules.* 



Analogous results have been obtained by Max Wichura's 

 experiments f in hybridizing Willows, who noticed the 

 following degrees of failure indicating the various amounts 

 of influence that the pollen-tube had over the sexual ap- 

 paratus of the plants crossed : (1) the ovaries swell and 

 ripen, but contain no seed ; . (2) the ovaries are quite filled 

 with silky hairs which clothe the umbilical cord end of the 

 seed, but contain no embryo ; (3) seeds are present, but 

 small and incapable of germination ; (4) seeds apparently 

 perfect, but do not germinate ; (5) seeds germinate, but the 

 seedlings are weak, and soon wither ; (6) seeds few but fertile 

 and active ; (7) seeds numerous with only a few fertile ; (8) 

 seeds numerous and fertile. 



* Gaertner, in his Memoire sur les Organes Reproducteurs des Phanero- 

 games, devotes a special chapter to the enlargement of the ovary without 

 previous pollination, with the result of a pseudo-fruit (Versuche u. 

 Beoh. iiher die Befrucht. Organe der Vollk. Gewdchse, 1844). 



t Die Bastardhefruchtung in Pjtanzenreich, erlautert an den Bastarden 

 der Deiden, Yon Max Wichura. Mit zwei Tafeln. 4to., Breslau, 1865. 

 Abstract by Rev. M. J. Berkeley, Journ. Roy. Hort. Soc, New Series, 

 vol. i., p. 57. 



