CHANGES OF THE ORGANS OF PLANTS. 209 



Feet above the level of the sea. 



The highest limit of pines under the equator 12,801 



The highest Hniit of trees under the equator 11,125 



Tlie highest limit of oaks under the equator 10,500 



The highest limit of the Peruvian bark tree 9,500 



The lowest limit of pines under the equator 5,685 



The highest limit of palms and bananas 3,280 



LECTURE XL. 



PLANTS AS AFFECTED BY CULTIVATION. CHANGE OF THE ORG^VNS. 



DISEASES. ^ECONOMICAL USES. 



322. It has been remarked, that though sjpecies may in some 

 respects be varied by cultivation, yet their distinctive charac- 

 ters will not be wholly lost. The differences which exist in 

 species are expressed by the terms 7xices^ varieties^ and varia- 

 tions. Races are those differences in a species w^hich are of a 

 striking kind, and continued from the parent to its offspring 

 by being propagated by the seed. They are produced by strew- 

 ing pollen of one species upon the pistils of another ; the seed 

 thus formed will produce a plant resembling both. Varieties are 

 a less important distinction than races ; they are not continued 

 by means of the seed, but produced by grafting or continuation 

 of the plant under some new circumstances. Yariations denote 

 the slightest kinds of difference ; they are occasioned by pecu- 

 liarities of climate, soil, moisture, dryness, &c. 



325. Metamor2?Jiosis.^ or cluinge of the organs ofj^lants. — The 

 organs of plants, owing to peculiar causes, often experience a 

 inetamorjyliosis^ and instead of their usual or normal appearance, 

 exhibit anomalies, or vegetable deformities. We here use the 

 term deformity, as signifying any variation from the ordinary 

 course of nature. The causes which produce these changes are : 



1st. The adhesion of ])arts usually separate ; thus we often 

 see flowers, leaves, and fruits united, and apjDearing double. 



It was asserted by De Candolle, many years since, that a 

 single petal which forms the corolla of many flowers, as the 

 stramonium or the blue-bell, is in reality composed of several 

 petals which become soldered, or cohere together before the 

 flower expands. The same botanist considered a monosepalous 

 calyx to be composed of several little leaves thus united before 

 their development. 



2d. Changes are occasioned hj a toant of sufficient vigor in 

 the 2)lcont to hring all parts to maturity. Some seeds thus often 



322. Permanenco of speciea — Races— Varieties— Variations.— 323. Metamorphosis of U'e organs o/ 

 plnnts — Adhesion. 



