CHANGES OF THE ORGANS OF PLANTS. 
209 
Feet above the level of tlie sea, 
The highest limit of pines under the equator. 
The highest limit of trees under the equator 
The highest limit of oaks under the equator 
The highest limit of the Peruvian bark tree. 
The lowest limit of pines under the equator 
The highest limit of palms and bananas 
12,801 
11,125 
10,500 
9,500 
5,685 
3,280 
LECTUEE XL. 
PLANTS AS AFFECTED BY CULTIVATION. CHANGE OF THE ORGANS. 
DISEASES. ^ECONOMICAL USES. 
322. It has been remarked, that though species 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 races^ varieties^ and varior 
tions. Races are those differences in a species which 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. Variations denote 
the slightest kinds of dift'erence ; they are occasioned by pecu- 
liarities of climate, soil, moisture, dryness, &c. 
323. Metamorjphosis^ or change of the organs of plants. — The 
organs of plants, owing to peculiar causes, often experience a 
metamorphosis^ 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 parts usually separate ; thus we often 
see flowers, leaves, and fruits united, and appearing 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 hy a want of sufficient vigor in 
the plant to hring all parts to maturity. Some seeds thus often 
32'2. Permanence of species — Races — Varieties — Variationa. — 323. Metaniorpliosis of ll'e organ ; « 
plun'jj -Adiiesion. 
