THE DISEASES OF PLANTS. 309 



Perennials, which live several years, perish ultimately of 

 the same disease. 



Caroline. And are there no means of diminishing the 

 number of seeds of annuals, and by thus preventing ex- 

 haustion, of transforming them into perennials? 



Mrs.B. This may be done by making the flower grow 

 double : the additional number of petals are produced at 

 the expense of the seed ; but requiring much less nour- 

 ishment, the plant is not exhausted. 



Emily. But, if trees perish only by accidental death, 

 some, at least, should escape ; for accidents do not always 

 occur. 



Mrs. B. Not, perhaps, to a certainty in any given 

 period ; but in the long course of time, they never fail to 

 happen ; and the extreme inequality in the length of life, 

 in trees of the same species, affords ground for believing 

 that its duration depends upon accident. 



Emily. But some kinds of trees are regularly much 

 longer-lived than others : the oak, for instance, than the 

 poplar ; forest, than fruit-trees. 



Mrs. B. Some plants are naturally much more robust 

 than others, and therefore resist during a longer period ac- 

 cidental attacks. The oak, so vigorous and magnificent 

 a tree ; out of six seeds which it produces in every blos- 

 som, brings only one to maturity ; and yet with how much 

 less effort could the oak ripen clusters of acorns than an 

 orchard tree the heavy load of fruit, under the weight of 

 which its branches bend ; and if any of them break, how 

 great is the probability that decay will ensue : the enfee- 

 bled vessels of the wood, exhausted by the labor of con- 

 veying sap to so much fruit, are unable to resist the con- 

 sequences of exposure to the weather ; and, after a series 

 of accidents of a similar nature during a course of years, 

 the tree at last perishes. When, therefore, it is said that 

 such a species of tree, usually lives such a number of 

 years, the duration refers to the average of time in which 

 it falls a sacrifice to accident. This average it is very 

 difficult to ascertain. i 



*. How may the number of seeds in annuals be diminished^ 

 1669. Why may not some trees live always, if they have only an acci- 

 dental deuthl 1670. What is said of the seeds of the oakits age, &c.1 

 1671. And of fruit trees! 1672. When it is said that certain specie! 

 of trees live so many years, what is to be understood 1 ? 



