34 FUNCTIONS OF PLANTS. 



pose carbonic acid, and yielding to the chemical influence of the oxygen of 

 the atmosphere, it dies and drops off. Those leaves are called deciduous 

 (09), which fall off in the autumn after the maturation of the shoots of the 

 current year ; those are called persistent (68), which remain on in a withered 

 state till the following spring; and those evergreen (66), which remain 

 attached and green till the following summer, or later. Some of these 

 evergreen leaves, as for example in certain species of Coniferse, remain on 

 for several years. 



126. The flowers of plants generally consist of the following parts : 

 1st, The floral envelopes consisting of the calyx or exterior covering, which 

 is generally green ; and the corolla or interior covering, which is commonly 

 of some other colour than green ; 2d, The organs of reproduction, comprising 

 the stamens and pistil ; and 3d, The germen or rudiment of the fruit and 

 seed. In general, the calyx and the corolla are present in every flower, and 

 also both sexes are contained in the same flower. But there are numerous 

 exceptions ; some flowers having a calyx without a corolla, as in Atragene ; 

 others having the calyx coloured, so as to resemble a corolla, as in Fuchsia 

 and many bulbs; many being without any floral envelopes, as hi the Wil- 

 low ; and the sexes being, in many cases, on different plants, as in Maclura 

 and Salisburm, Populus and alix. No flower in a natural state, how- 

 ever, is to be found in which there is not present one or other of the sexes, 

 excepting double flowers, which are monstrosities, and those of some hybrids, 

 which are anomalies. 



127. The floral envelopes may be considered as making the nearest ap- 

 proach to common leaves ; and in many plants, particularly such as are in 

 a high state of cultivation, they assume the appearance of leaves ; as, for 

 example, in some varieties of Rose. In many plants the sexes are also 

 changed into leaves, and this is the mode in which most double flowers are 

 produced. Occasionally both the floral envelopes and the sexes are turned 

 into leaves, as is found occasionally in wet seasons in the flowers of the 

 common Parsley. In the earlier stages of the progress of gardening in 

 Britain, when few plants were introduced from foreign countries, the great 

 object of the curious cultivator was to produce double flowers, and other 

 monstrosities ; and hence we have double-flowered varieties of most of the 

 ornamental herbaceous plants that have been long in cultivation, and even of 

 some trees and shrubs, such as the double-blossomed cherry, double- blos- 

 somed hawthorn, double-blossomed peach, &c. 



128. The art of causing plants to produce flowers sooner than they would 

 do naturally, is one of great importance to the cultivator. The principle on 

 which it is founded seems to be that of causing a greater accumulation of 

 nutritive matter in the particular part of the plant intended to produce 

 flowers than is natural to that part ; or in the case of annual plants, to con- 

 centrate the nutritive matter of the entire plant, by growing it in a dryer 

 soil than that which is natural to it. Hence by ringing any particular branch 

 of a tree, blossom-buds will be formed on the part of the branch above the 

 ring, while shoots more watery than usual will be formed below it. Hence, 

 also, by grafting a shoot from a seedling tree on the extremities of the 

 branches of a full-grown tree of the same species, blossoms will be produced 

 some years sooner than would have been the case had the branch remained 

 on its parent plant. In this way new kinds of fruit, raised from seed, may 

 be proved much sooner than if the seedling plants were left a sufficient 



