INTRODUCTION 



ing problems connected with the question of their pollination and fertilisa- 

 tion. Nearly all the species dealt with in this work belong to one or other 

 of two great classes of Flowering Plants, the Dicotyledons and Gymnosperms, 

 the Monocotyledons being represented by a very few species. The Gymno- 

 sperms, or plants with naked ovules, have flowers which are unisexual and 

 destitute of calyx and corolla, and are entirely wind-fertilised. There is a 

 general broad resemblance of structure in the various genera and species, 

 and the fertilised ovules take from one to three years to become ripe seeds. 

 In the Dicotyledons we have a marvellous diversity of floral structure, and 

 there is no doubt that each peculiarity has its own significance. 



Generally speaking, self-fertilisation is not advantageous to the plant, and 

 the structural differences are usually a means of preventing this, and at the 

 same time an aid to cross-pollination. Our catkin-bearing trees are con- 

 spicuous examples of this, for their flowers are nearly all anemophilous, the 

 females having well-developed and usually projecting stigmas, and the male 

 flowers being easily shaken in the wind, while, as an aid to the better dis- 

 persal of their pollen by the wind, they almost universally blossom before 

 the leaves are fully developed. Irregular and conspicuously coloured flowers 

 are nearly always pollinated by insects, and our trees and shrubs provide us 

 with many examples, the greater number perhaps belonging to the Order 

 LeguminosEe. The latter are for the most part pollinated by bees, but 

 among entomophilous flowers we have many which for the perpetuation of 

 the species are dependent on the visits of butterflies or moths, wasps, flies, or 

 beetles. We cannot stay to discuss the many questions connected with colour, 

 perfume, nectaries, &c, but will direct the reader to the very admirable 

 chapters on the subject to be found in various well-known botanical works. 



COMMERCIAL PRODUCTS OF FLOWERS OF TREES 



AND SHRUBS 



As commercial products the flowers of trees and shrubs are of not much 



value, but in two instances the unopened flower-buds are used commercially, 



viz., in the case of Capers, which are produced on a small shrub (Cappa?'is 



xvi 



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