280 MR. A. W. BENNETT ON CLEISTOGAMIC FLOWERS. 



a study of pollen must be familiar -with the fact that the emission 

 of tubes by pollen-grains while still within the anther is by no 

 means an uncommon occurrence. Robert Brown and Baillon have 

 indeed observed them to attain a considerable length. But this 

 offers scarcely any explanation of the extraordinary fact that in 

 these closed flowers the pollen-tubes will reach the stigmatic sur- 

 face or cavity after travelling for a considerable distance through 

 the air in a straight line from the anthers, vertically upwards in 

 the case of Oxalis, horizontally in others ; while in Viola canina, 

 according to Von Mold's description, they creep for a distance 

 along the surface and over the back of the ovary. None are seen 

 wandering aimlessly about in uncertainty ; they all seem guided by 

 some unseen agency in the required direction ; and yet an expe- 

 riment of Darwin's Q Forms of Flowers/ p. 337) sufficiently shows 

 that when not in proximity to the stigma, pollen-grains protrude 

 their tubes in all possible directions. I may add that I have 

 never seen myself, nor do I find it stated in any trustworthy de- 

 scription, that the pollen-tubes ever actually perforate the wall of 

 the anther in order to reach the stigma in cleistogamic flowers, 

 as is stated to be the case in Juncus bufonius*; they always make 

 their way either through terminal pores, or, as Von Mohl describes 

 it, through the sutures of the anther. It seems hardly possible 

 to attribute to heredity only such an apparently spontaneous ten- 

 dency. If pollen-grains are able through many generations 

 to acquire such a power as this, all need for an exciting stigmatic 

 surface, and even for the carriage of pollen to the stigma, would 

 seem to be obviated. The subject certainly deserves much closer 

 and fuller investigation than it has yet received. 



* 



Note. — Since the above paper was written, two papers have 

 been published containing drawings of cleistogamic flowers, both 

 by the Bev. G-. Henslow. In the ' Transactions of the Linnean 

 Society,' Botany, 2nd series, vol. i. p. 317, are drawings of the 

 closed self-fertilized flowers of Viola odorata and V. canina, Oxalis 

 Acetosella, Lamium amplexicaule, Egiphegus virginiana, and Sor- 

 deum rnurinum ; and in the ' Popular Science Review' for Jan. 

 1879, of most of the same species, as well as many others. Both 

 are accompanied by excellent descriptions. 



* See Batalin in ' Botanische Zeitung,' 1871, vol. xxix. p. 388. 



