434 ON THE DIRECT ACTION OF THE Chap. XI. 



flowers. Gartner gradually increased the number cf pollen 

 grains until he succeeded in fertilising a Malva, ana has^*^ 

 proved that many grains are first 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 formed without any embryo being developed 

 within. Prof. Hildebrand, also, has lately shown ^'^^ that, in 

 the normal fertilisation of several Orchideaj, 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 have reached the ovules, 

 but even before the placentas and ovules have been formed ; 

 so that with these orchids the pollen acts directly on the 

 ovarium. On the other hand, we must not overrate the effi- 

 cacy of pollen in the case of hybridised plants, for an embryo 

 may be formed and its influence excite the surrounding tissues 

 of the mother-plant, and then perish at a very early age 

 and be thus overlooked. Again, it is well known that with 

 many plants the ovarium may be fully developed, though 

 pollen be wholly exch;ded. Lastly, Mr. Smith, the late 

 Curator at Kew (as I hear through Dr. Hooker), observed 

 with an orchid, the Bonatea speciosa, the singular fact that the 

 development of the ovarium could be effected by the mechanical 

 irritation of the stigma. Nevertheless, from the number of 

 the pollen-grains expended " in the satiation of the ovarium 

 and pistil," — from the generality of the formation of the 

 ovarium and seed-coats in hybridised plants which produce 

 no seeds, — and from Dr. Hildebrand's observations on orchids, 

 we may admit that in most cases the swelling of the 

 ovarium, and the formation of the seed-coats are at least 

 aided, if not wholly caused, by the direct action of the pollen, 

 independently of the intervention of the fertilised germ. 

 Therefore, in the previously given cases we have only to 



'^' ' Beitrage zur Kenntniss der Wirkuna; Jes Pollens,' ' Rotanische 



Befruchtung,' 1844, s. 347-351. Zeitimg,' No. 44 et seq., Oct. 33, 186.> ; 



'5» 'Die Fruchtbildung der Orchi- and Aug. 4, 1865,. s. 249. 

 deen, ein Beweis fiir die doppelte 



