68 INTRODUCTION TO PLANT GEOGRAPHY [CHAP 



which produces the seed or seeds internally. After fertilization, the 

 ovary becomes the fruit. The Angiosperms are also generally to 

 be distinguished from the Gymnosperms by their internal structure 

 and by their possession of flowers, which are specialized short 

 reproductive shoots bearing typically four different sets of organs 

 in close proximity. These are (i) on the outside the sepals, which 

 are usually leaf-like and protective in the bud stage, and inside of 

 which come (2) the petals, which are commonly attractive in colour, 

 form, and odour ; then (3) the stamens, producing the pollen grains 

 (microspores), and finally (4) the one or more carpels lying in the 

 centre and producing the ovule or ovules. 



Various types of Angiosperms are so entirely familiar to us all 

 that it would be superfluous to illustrate them here. Instead, Fig. 19 

 (pp. 70-71) shows a diagrammatic representation of a dicotyledon- 

 ous {see p. 73) Angiosperm flower, and, in addition, sections of 

 stems of monocotyledonous {see p. 73) and dicotyledonous plants 

 to indicate the disposition and something of the appearance of the 

 vascular bundles when magnified. Many examples of Angiosperms 

 will be found illustrated in the chapters on vegetation (especially 

 Chapters XII-XIV), and of their fruits and seeds there are accounts 

 in Chapter IV, whilst the two main groups of them. Monocotyledons 

 and Dicotyledons, are distinguished in the last paragraph of the 

 present chapter. Familiar Angiosperms include all of our common 

 agricultural and garden crops, all Grasses and other flowering herbs 

 whether annual or perennial, and almost all broad-leafed trees and 

 shrubs such as Oaks, Elms, Beeches, Maples, Birches, Poplars, and 

 Willows. There is consequently no need to emphasize that each 

 consists primarily of roots, stem or stems, and leaves, nor to describe 

 the form of these organs. 



Sexual reproduction is the object of the flowers and with it the 

 stamens and carpels are particularly concerned. Frequently the 

 stamens and carpels are in different flowers or even on different 

 plants, in which event the individuals are unisexual. In any case 

 the function of the stamens is to produce the pollen grains, usually 

 in large numbers, for transference (by such agencies as wind, animals, 

 or water) to the stigma, which is the receptive part of the carpel. 

 Within this last the ovules are formed, each containing a female 

 gamete. The pollen grains germinate on the stigma, sending out 

 pollen tubes which come to contain the male gametes and usually 

 grow through the underlying tissue, deriving nourishment as they 

 go. This growth of pollen tubes normally goes on until the tip of 



