300 LONGEVITY OF PLANTS. 



other, either by fastening, themselves upon their surfaces, or 

 by so near a location as to deprive others of their necessary 

 food. Parasites fasten themselves upon the surfaces of other 

 plants ; they are distinguished into two kinds, the false and 

 true parasites ; the former adheres to the plant without feeding 

 on its juices, as mosses and lichens. These derive their nour- 

 ishment from the atmosphere, but they injure the tree by har- 

 boring insects, and attracting moisture, which often rots the 

 part of the stem on which they grow. The misletoe is a true 

 parasite whose root, piercing the bark of trees, plants itself in 

 the alburnum, and absorbs food from it, in the same manner as 

 if it were fixed in the soil. The Pterospora is a very curious 

 parasite which is sometimes found upon the leaves of shrubs,* 

 but more frequently upon the branches and leaves of trees. 

 Mushrooms are of the class of false parasites. Smut is a black 

 fungus, which fastens itself upon the ears of oats and other grain. 

 The rot is a fungus excrescence which preys upon the seed ; if 

 seeds which have this disease fastened upon them are sown, the 

 rot will be propagated also. Ergot is a disease mostly confined 

 to rye. Rust is chiefly confined to the grasses ; both are of the 

 fungi family. 



6th. Diseases resulting from age. Plants differ from animals 

 in one important circumstance ; the latter develope their organs 

 at once, these organs in progress of time become indurated 

 and obstructed, until they at length decay from old age. Plants, 

 on the contrary, renew themselves every year ; that is, they 

 form new vessels to convey the juices, new leaves to elaborate 

 them and new buds to produce flowers and fruits. Plants do 

 not, then, like animals, seem destined to die with old age; or 

 there does not seem to be in perennial plants any prescribed 

 term of existence. The producing of fruit appears to exhaust 

 the vital energy of the plant, in annuals in one year, in bien- 

 nials in two, in perennials, in a longer or shorter period ac- 

 cording to their natural constitution, and the quantity of fruit 

 which they produce. Apple trees which bear heavy loads of 

 fruit, are very short lived in comparison with the oak, which 

 perfects from each flower, but one of six seeds, and this fruit is 

 but a small acorn. 



There are some trees now known to exist, which are supposed 

 to be of great age ; in the Island of Teneriffe is the DRACAENA 

 draco, which according to many circumstances may seem to 



* A species of this genus was found in the woods east of Troy, upon the leaf 

 of the Vaccinium. The colour of the whole plant, consisting of two flowera, 

 and a kind of leaf, was that of a red rose. 



5th. Parasites 6th. Diseases resulting from old age Aged tree*. 



