cider of surpassing excellence; having become feeble, diseased and almost if not quite ex- 

 tinct. Such then, when they come to be examined, are the facts and arguments advanced 

 by Dr. Lixdlkv in support of his assertion that " there is not only no proof of the cor- 

 rectness of Mr. Knight's theory, but the strongest presumption to the contrary." 



As in the case of the natural death of forest trees, the facts are too numerous and too 

 well authenticated, proving that valuable varieties of plants propagated by extension, 

 have ultimately become diseased and unproductive, and con-sequentl}' extinct. 



Dr. Lindley thus explains these facts — "a tree is allowed from some cause or other to 

 become unhealthy, a piece cut from it and put upon another tree, carries its disease with 

 it; when again divided, the disease is again propagated; and this will go on so long as the 

 unhealthy plants remain exposed to the circumstances which originally caused their bad 

 health." 



Adverse circumstances certainly tend to make plants unhealthy, and a variety of apple 

 which has been in existence two hundred years is likely to have been exposed to a greater 

 amount of damaging influences than a variety which has been in existence only fifty years; 

 therefore we may reasonably conclude that the old variety, owing to the effect of these 

 adverse external influences alone, will be less healthy than the younger variety. 



Dr. LiNDLEY may tell us that disease does not arise from internal but external circum- 

 stances. But the question will intrude, how are we to avoid these circumstances? what 

 is " the some cause or other" which makes them unhealthy.^ If the plants of a variety 

 in a certain locality only become diseased, then we might have some grounds for hope, 

 but when we remember that of the apples mentioned by Parkinson, the names only re- 

 main, and when we now know that old varieties of the apple and pear decline in vigor and 

 productiveness, first in cold wet ungenial soils; lastly in warm dry situations, how are 

 we to prevent this.'' " Change the circumstances; keep off the cause of the evil and the evil 

 will gradually disappear as in the case of the Golden Pippin." Are we then to establish 

 a plant hospital in the South of France or in Madeira; what other means are we to resort 

 to, seeing that the Golden Pippin is the only instance mentioned of trees of an almost worn 

 out variety existing in a comparative state of health. 



The duration of both animal and vegetable life depends upon the original vigor of the 

 constitution as well as adventitious circumstances. There are inherent as well as external 

 influences with which we have to contend. Thus of human beings; many die in infancy, 

 others may live a century. Of ten thousand born, hardly one may die through exhaus- 

 tion of vitality, or sheer old age, — I mean, without the exhibition of any active disease. 

 Again, of two children born with equally vigorous constitutions; one whose constitution 

 has been subject to many trials may die in forty years, whilst the other more favorably 

 circumstanced may live double that time. In like manner individual seedling plants 

 differ greatly in constitutional vigor. Some we find are so weak that the first adverse in- 

 fluence to which they may be exposed destroys them, whilst other plants of the like kind 

 and age, growing under the same circumstances, remain unharmed. Why is this? Be- 

 cause of the difl'erence in constitutional vigor. Some external influence may have been 

 the immediate cause of death, but the inherent feebleness of the plant was the predisposing 

 cause which led to its destruction. So of plants with originally vigorous constitutions; 

 few majr die simply of exhaustion of vitality, and a tree in the prime of its existence may 

 become unhealthy and diseased from various external causes; the soil maybe wet or other- 

 wise unsuitable, the roots may wander into an ungenial subsoil, or the leaves in an ad- 

 verse season may be attacked by fungi, &c. But improve the soil, replant the trees 

 prevent their roots from reaching the subsoil, or let the fungi disappear, and the 



