Chap. XVIII. DEVELOPMENT OF THE ORGANS OF VEGETATION. 169 



tap-roots are cut or mutilated. 101 So it is with hybrids ; for instance, Prof. 

 Lecoq 102 had three plants of Mirabilis, which, though they grew luxu- 

 riantly and flowered, were quite sterile ; but after beating one with a stick 

 until a few branches alone were left, these at once yielded good seed. The 

 sugar-cane, which grows vigorously and produces a large supply of suc- 

 culent stems, never, according to various observers, bears seed in the 

 West Indies, Malaga, India, Cochin China, or the Malay Archipelago. 103 

 Plants which produce a large number of tubers are apt to be sterile, as 

 occurs, to a certain extent, with the common potato; and Mr. Fortune 

 informs me that the sweet potato ( Convolvulus batatas) in China never, as 

 far as he has seen, yields seed. Dr. Eoyle remarks 104 that in India the 

 Agave vivipara, when grown in rich soil, invariably produces bulbs, but 

 no seeds ; whilst a poor soil and dry climate leads to an opposite result. 

 In China, according to Mr. Fortune, an extraordinary number of little 

 bulbs are developed in the axils of the leaves of the yam, and this plant 

 does not bear seed. Whether in these cases, as in those of double flowers 

 and seedless fruit, sexual sterility from changed conditions of life is the 

 primary cause which leads to the excessive development of the organs 

 of vegetation, is doubtful; though some evidence might be advanced in 

 favour of this view. It is perhaps a more probable view that plants 

 which propagate themselves largely by one method, namely by buds, have 

 not sufficient vital power or organised matter for the other method of 

 sexual generation. 



Several distinguished botanists and good practical judges believe that 

 long-continued propagation by cuttings, runners, tubers, bulbs, &c, inde- 

 pendently of any excessive development of these parts, is the cause of 

 many plants failing to produce flowers and of others failing to produce 

 fertile flowers, — it is as if they had lost the habit of sexual generation. 105 

 That many plants when thus propagated are sterile there can be no doubt, 

 but whether the long continuance of this form of propagation is the actual 

 cause of their sterility, I will not venture, from the want of sufficient 

 evidence, to express an opinion. 



That plants may be propagated for long periods by buds, without the 

 aid of sexual generation, we may safely infer from this being the case 

 with many plants which must have long survived in a state of nature. 

 As I have had occasion before to allude to this subject, I will here give 

 such cases as I have collected. Many alpine plants ascend mountains 

 beyond the height at which they can produce seed. 106 Certain species of 



101 Ingledew, in ' Transact, of Agri- of Hort. Soc.,' vol. i., 1846, p. 254— Dr. 

 cult, and Hort. Soc. of India,' vol. ii. Wight, from what he has seen in India, 



102 ' De la Fe'condation,' 1862, p. 308. believes in this view ; ' Madras Journal 

 10a Hooker's « Bot. Misc.,' vol. i. p. of Lit. and Science,' vol. iv., 1836, p. 



99 ; Gallesio, ' Teoria della Kipro- 61. 



duzione,' p. 110. 106 "VVahlenberg specifies eight species 



104 ' Transact. Linn. Soc.,' vol. xvii. in this state on the Lapland Alps : see 

 P- 563. Appendix to Linnaeus' ' Tour in Lap- 



105 Godron, < De l'Espece,' torn. ii. p. land/ translated by Sir J. E. Smith, 

 106 ; Herbert on Crocus, in ' Journal vol. ii. pp. 274-280. 



