402 ON THE DIRECT ACTION OF THE Chap. XI ^ 



and other fruit-trees. There is not the least reason to believe 

 that a branch which has borne seed or fruit directly modified by 

 foreign pollen is itself affected, so as subsequently to produce 

 modified buds: such an occurrence, from the temporary con- 

 nection of the llower with the stem, would be hardly possible. 

 Hence but very few, if any, of the cases of sudden modifications 

 in the fruit of trees, given in the early part of this chapter, 

 can be accounted for by the action of foreign pollen ; for such 

 modified fruits have commonly been afterwards propagated by 

 budding or grafting. It is also obvious that changes of colour 

 in the flower which necessarily supervene long before it is ready 

 for fertilisation, and changes in the shape or colour of the leaves, 

 can have no relation to the action of foreign pollen : all such 

 cases must be attributed to simple bud-variation. 



The proofs of the action of foreign pollen on the mother- 

 plant have been given in considerable detail, because this action, 

 as we shall see in a future chapter, is of the highest theoretical 

 importance, and because it is in itself a remarkable and apparently 

 anomalous circumstance. That it is remarkable under a physi- 

 ological point of view is clear, for the male element not only 

 affects, in accordance with its proper function, the germ, but the 

 surrounding tissues of the mother-plant. That the action is 

 anomalous in appearance is true, but hardly so in reality, for 

 apparently it plays the same part in the ordinary fertilisation of 

 many flowers. Gartner has shown, 135 by gradually increasing 

 the number of pollen-grains until he succeeded in fertilising a 

 Malva, that many grains are expended in the development, or, 

 as he expresses it, in the satiation, of the pistil and ovarium. 

 Again, when one plant is fertilised by a widely distinct species, 

 it often happens that the ovarium is fully and quickly developed 

 without any seeds being formed, or the coats of the seeds 

 are developed without an embryo being formed within. Dr. 

 Hildebrand also has lately shown in a valuable paper 136 that, 

 with several Orchideae, the action of the plant's own pollen is 

 necessary for the development of the ovarium, and that this 

 development takes place not only long before the pollen-tubes 



135 'Beitrage zur Kenntniss der Be- kung des Pollen,' Botanische Zeitung, 

 fruchtung,' 1844, s. 347-351. No. 44 et seq.,. Oct. 30, 1863 ; and 



136 'Die Fruchtbildung der Orchi- 1865, s. 249. 

 deen, ein Beweis fur die doppelte Wir- 



