408 SELECTING AND IMPROVING PLANTS IN CULTURE, 



withdrawn, and that extraordinary supplies of nourishment and moisture, as 

 in moist and warm seasons, produce flowers more double than in dry 

 seasons. Mr. Munro, a scientific practical gardener, endeavours to account 

 for the production of double flowers, by supposing that there is one fluid or 

 sap of plants destined for growth, and another for reproduction ; and that 

 double flowers are produced when the latter sap is in excess. He concludes, 

 therefore, that by reducing the number of seed-pods in a plant, those left 

 would be so amply nourished by the excess of the reproductive sap, as to 

 produce double flowers. To prove this he selected a number of single scarlet 

 ten-week stocks, and as soon as he observed five or six seed-pods fairly 

 formed on the flower-spike, every succeeding flower was pinched off. From 

 the seeds saved in this manner he had more than 400 double flowers from 

 one small bed of plants (G. M. for 1838, p. 122). De Candolle states that 

 Mr. Salisbury assured him that by putting plants with single flowers in a 

 very rich soil, and fixing ligatures round the stem near the neck, he obtained 

 seeds which produced double flowers (Phys. Feg., p. 734) ; but this as a 

 general principle he considers very doubtful. One thing is certain, that 

 seeds saved from semi-double flowers frequently produce flowers which are 

 double ; and it would also appear that from the authority of gardeners/seeds 

 from single flowers which have been growing among double ones, more 

 frequently produce double flowers, than seeds from plants which have not 

 been so circumstanced. 



869. Duration of varieties. All the plants of a variety which have 

 been procured by division, for example all the plants of any particular 

 variety of grape, apple, or potato, being in fact only parts of one individual, 

 it has been argued by Mr. Knight, that when the parent plant dies all 

 the others must die also ; or to put the doctrine in a more general form, 

 that all varieties are but of limited duration. This opinion, though it 

 has been adopted by many persons, has not met with the approbation of 

 Professor De Candolle, who says that the permanence of the duration of 

 varieties, so long as man wishes to take care of them, is evident from the 

 continued existence of varieties the most ancient of those which have 

 been described in books. By negligence, or by a series of bad seasons, 

 they may become diseased, like some of our varieties of apple or potato ; but 

 by careful culture they may be restored and retained to all appearance for 

 ever. We are not sure that De Candolle's theory will hold good with the 

 finest fruits and florists' flowers. The species might be recovered, but we 

 question whether in many instances that will be the case with the variety. 

 Perhaps a hypothesis might be devised which would coincide with both 

 authorities. It would coincide with that of De Candolle, if Mr. Knight had 

 spoken with reference to actually wild varieties only ; but with regard to 

 improved varieties, as they are understood in a horticultural point of view, 

 they are doubtless prone to decay in proportion to their degree of departure 

 from that physiological perfection which enables the wild variety to maintain 

 itself continually on the surface of the globe, independent of the care of man. 

 A wild variety will produce seed under favourable circumstances, but 

 many highly improved varieties, in a horticultural sense, do not perfectly 

 mature their seeds under any circumstances whatever ; and therefore must 

 be physiologically imperfect, and being so, a priori^ if it be admitted that 

 imperfection is a principle of decay, it will not be denied, that no plant 



