DURATION OF VARIETIES OF PLANTS 



newal or reproduction, as by seed. They will all exhibit, (if we may so speak,) a sympa 

 thetic state of health, making, of course, due allowance for the action of adventitious cir- 

 cumstances; and although some plants, if placed in unusually favorable circumstances, 

 may out-live tlie parent tree, yet there will come a time " beyond which the debility inci- 

 dent to old age, cannot be stimulated;" all plants of the variety will consequently be- 

 come diseased and worthless. 



A knowledge of this hypothesis is of importance to all cultivators, because if it is well 

 founded, it shows to us the hopelessness of striving against nature, by persevering in the 

 cultivation of varieties of plants when they have become aged and unhealthy, and no lon- 

 ger able to make an adequate return for the labor and attention bestowed on them. It 

 shows also, the necessity of keeping up a succession of varieties from seed, and that it is 

 an important matter to consider the age and health of a variety, when our object is to ob- 

 tain from seed, new, improved, and healthy varieties. 



In order that Mr. Knight's hypothesis may be better understood, generally, and that 

 I may be better able to prove what substantial grounds it rests upon, I have thought it 

 advisable to direct attention to the most recent and elaborate attack on it — viz : two arti- 

 cles of Prof. LiNDLEY, in the Gardeners' Chronicle of December 13 and 20, 1845; for the 

 value of a theory is made manifest not only by the accuracy of the facts on which it is 

 based, or the soundness of the reasoning by which it is supported, but by the fallacy of 

 the arguments by which it is assailed, more especially if the assailant is a man of acknow- 

 ledged ability, and acquainted with the subjects on which he writes. 



The opinion of systematic botanists generally, on horticultural matters, — I mean men 

 whose lives have been chiefly devoted to the classification and description of plants, does 

 not seem, so far as my experience extends, to be entitled to any very great weight. 

 LiNDLEY, however, is an exception — the son and brother of a nurseryman, Vice-Secretary 

 of the Horticultural Society of London, and Editor of the Gardeners' Chronicle, he has 

 enjoyed opportunities of obtaining a more thorough knowledge of the details of practice, 

 and the history of cultivated plants, than any other man now living who possesses any- 

 thing like the same amount of theoretical knowledge; and when, with these advantages, 

 we consider that he wields the pen of a ready and plausible writer, it may be presumed 

 that if any man were capable, by means of facts at present known, of proving that Mr. 

 Kkight's views on this point are erroneous, Lindley would assuredly be that man. 



Possibly there may be readers of the Horticulturist not much acquainted with Mr. 

 Knight's labors, aud who may not, therefore, be able to appreciate the deference which 

 is due to him as a patient, ingenious, and truth seeking inquirer. No one can better testi- 

 fy to his great merits than Dr. Lindley. In a memoir of Mr. Knight, published in the 

 Atheneum, Dr. Lindley, when alluding to his celebrated paper on the inheritance of dis- 

 ease in fruit trees, and other communications laid before the Royal Society, said, " in all 

 these researches the originality of the experiments was very remarkable, and the care 

 with which the results were given, was so great, that the most captious of subsequent 

 writers have admitted the accuracy of the facts produced by Mr. Knight, however much 

 they may have differed from him in the conclusions which they drew from tliem. No man 

 living, now before the world, can be said to rank with him in that particular branch of 

 science to which his life was devoted." 



One of the first subjects to which Mr. Knight's attention was directed, was the un- 

 healthy condition of several old and famous varieties of the apple and pear; he was told 

 ghboring nurserymen that they could no longer raise healthy and profitable trees 

 them ; that they were, in fact, worn out. Mr. Knight was persuaded that this was 



No. X. 



