196 Prof. Asa Gray on the Question 
and have lost none of their force since. Weeping willows, 
bread-fruits, bananas, sugar-cane, tiger lilies, Jerusalem arti- 
chokes, and the like have been propagated for a long while in 
this way without evident decadence. 
Moreover the analogy upon which his hypothesis is founded 
will not hold. Whether or not one adopts the present writer’s 
conception, that individuality is not actually reached or main- 
tained in the vegetable world, it is clear enough that a common 
plant or tree is not an individual in the sense that a horse or 
man, or any one of the higher animals, is—that it is an indi- 
vidual only in the sense that a branching zoophyte or mass of 
coral is. Solvitur crescendo: the tree and the branch equally 
demonstrate that they are not individuals, by being divided 
with impunity and advantage, with no loss of life, but much 
increase. It looks odd enough to see a writer like Mr. Sisley 
reproducing the old hypothesis in so bare a form as this— [ 
am prepared to maintain that varieties are individuals, and 
that as they are born they must die, like other individuals.”’ 
“ We know that oaks, sequoias, and other trees live several 
centuries; but how many, we do not exactly know. But that 
they must die, no one in his senses will dispute.” Now what 
people in their senses do dispute is, not that the tree will die, 
but that other trees, established from cuttings of it, will die 
with it. 
But does it follow from this that non-sexually propagated 
varieties are endowed with the same power of unlimited dura- 
tion that are possessed by varieties and species propagated 
sexually (¢.e. by seed) ? ‘Those who think so jump too soon at 
their conclusion. For, as to the facts, it is not enough to 
point out the diseases or the trouble in the soil or the atmo- 
sphere to which certain old fruits are succumbing, nor to prove 
that a parasitic fungus (Peronospora infestans) 1s what is the 
matter with potatoes. For how else would constitutional 
debility, if such there be, more naturally manifest itself than 
in such increased liability or diminished resistance to such 
attacks? Andif you say that anyhow such varieties no not 
die of oldage (meaning that each individual attacked does not 
die of old age, but of manifest disease), it may be asked in 
return, What individual man ever dies of old age in any other 
sense than of a similar inability to resist invasions which in 
earlier years would have produced no noticeable effect ? Aged 
people die of a slight cold or a slight accident ; but the inevit- 
able weakness that attends old age is what makes these slight 
attacks fatal. 
Finally, there is a philosophical argument which tells 
strongly for some limitations of the duration of non-sexually- 
