364 PHYTOLOGY. 



similar to those whose stalks only live the same summer, but the roots 

 live, and shoot out new stalks ; however, it is never the last or former 

 year's shoots that throw out leaves, it is a new shoot. 



The second is what may he called , or the second 



season of its age, or when it has finished the second growth. This 

 would be similar to the Raspberry ; for the Raspberry does not die in 

 the same season of growth, as many vegetables do, but in the second 

 season, as do the leaves of .the Scotch and "Weymouth Pines, Laurel, &c. 



The third may be called , or the third season of its 



age, or when it has finished its third shoot, as in the 



There may be a fourth, a fifth, a sixth difference in regard to the 

 times of casting the leaves ; the last of which seems to be the case with 

 the Spruce. Every winter exemplifies the first class, and in all of the 

 Pine-kind this fact is easily known ; but in most others of the second, 

 third, &c. [difference as to times] the facts can only be known by a 

 succession of observations. 



The casting of the leaves of plants is most probably similar to 

 sloughing or exfoliation in animals. It is at least an operation of 

 the plant, producing a separation of the leaf; and the only thing that 

 proves it is, that the leaf will not fall off if the plant, and of course 

 the leaf, be dead ; but if the leaf dies, although long before its destined 

 time, it withers, is separated, and falls off; but if both the plant and 

 leaves die at the same time, viz. before the separation has taken place, 

 then the leaf will not fall off, even when dried. 



These facts show gardeners whether a new transplanted plant is 

 dead or alive. If the leaves fall off by passing the hand over them, 

 then they are sure the plant is alive ; but if they do not fall off of 

 themselves, nor can be separated by passing the hand over them, then 

 it is most probable that the plant is dead. 



Of the Change of the Colour of Leaves and StalJcs of Vegetables from 

 the Green to the Yellow when dying. — This change is an operation of the 

 living powers of the plant, and not simply death taking place. It is 

 extremely gradual when the part is as it were allowed to die a natural 

 death ; but either a great drought or a few frosty evenings will hasten 

 on the decline, and they die sooner or faster. That it is an operation 

 of the plant arising from debility or the stimulus of death, is, I think, 

 evident ; for if a plant in full vigour, in which it is at the greenest, be 

 killed immediately, by putting it into boiling water or by electricity, it 

 retains its green coloiu - , and will die green, and even dry that colour : 

 whence we may suppose that the strongest plants, or those with the 

 greatest powers of action of any one species, will be of the deepest 

 green ; and I believe that this is shown every day by experience. 



