154 



STERILITY. 



Chap. XVIII 



ascend mountains beyond the height at which they can produce 

 seed.^^° Certain species of Poa and Festuca, when growing on 

 mountain-pastures, propagate themselves, as I hear from Mr. 

 Bentham, almost exclusively by bulblets. Kalm gives a more curious 

 instance ^^^ of several American trees, which grow so plentifully in 

 marshes or in thick woods, that they are certainly well adapted for 

 these stations, yet scarcely ever produce seeds ; but when acciden- 

 tally growing on the outside of the marsh or wood, are loaded with 

 seed. The common ivy is found in Northern Sweden and Eussia, 

 but flowers and fruits only in the southern provinces. The Acorus 

 calamus extends over a large portion of the globe, but so rarely 

 perfects fruit that this has been seen only by a few botanists, 

 according to Caspary, all its pollen-grains are in a worthless condi- 

 tion."^ The Hypericum caJycinum, which propagates itself so freely 

 in our shrubberies by rhizomes, and is naturalised in Ireland, 

 blossoms profusely, but rarely sets any seed, and this only during 

 certain years; nor did it set any when fertilised in my garden by 

 pollen from plants growing at a distance, Tiie Ly^imachia riummu- 

 lai'iriy which is furnished with long runners, so seldom produces 

 seed-capsules, that Prof. Decaisne,"^ who has especially attended to 

 this plant, has never seen it in fruit. The Carex rigida often fails 

 \o perfect its seed in Scotland, Lapland, Greenland, Germany, and 

 New Hampshire in the United States."* The periwinkle ( I'inca 

 irunor), which spreads largely by runners, is said scarcely ever to 

 produce fruit in England ; "^ but this plant requires insect-aid for 

 its fertilisation, and the proper insects may be absent or rare. The 

 Jusst'oea graridiflora. has become naturalised in Southern France, and 

 has spread by its rhizomes so extensively as to impede the naviga- 

 tion of the waters, but never produces fertile seed,"^ The horse- 

 radish {Cochlearia armoracia) spreads pertinaciously and is natural- 

 ised in various parts of Europe ; though it bears flowers, these 

 rarely produce capsules : Professor Caspary informs me that he has 

 watched this plant since 1851, but has never seen its fruit; 65 per 

 cent, of its pollen-grains are bad. The common llanunculus ficaria 

 rarely bears seed in England, France, or Switzerland ; but in 1863 

 I. observed seeds on several plants growing near my house."" Other 



^'" Wahlenberg specifies eight 

 species in this state on the Lapland 

 Alps : see Appendix to Linnaeus' ' Tour 

 in Lapland,' translated by Sir J. E. 

 Smith, vol. ii. pp. 274-280. 



''' 'Travels in North America,' 

 Eng. translat., vol. iii. p. 175. 



^'2 With respect to the ivy and 

 Acorus, see Dr. Bromfield in the ' Phy- 

 tologist,' vol. iii. p. 376. Also Lind- 

 lev and Vaucher on the Acorus, and 

 see Caspary as below. 



^" 'Annal. des Sc. Nat.,' 3rd series, 



ZooL, torn. iv. p. 280. Prof. Decaisne 

 refers also to analogous cases with 

 mosses and lichens near Paris. 



"•• Mr. Tuckermaun, in Silliman's 

 'American Journal of Science,' vol. 

 xlv. p. 1. 



>i^ Sir J. E. Smith, ' English Flora,' 

 vol. 1. p. 339. 



"« G. Planchon, 'Flora de Mont- 

 pellier,' 1864, p. 20. 



^^' On the non-production of seeds 

 in England, see Mr. Crocker, in ' Gar- 

 dener's Weekly Magazine,' 1852, p. 



