552 



BOTANY 



PART II 



methods leading to this common end are, however, very various. In 

 contrast to the Bryophyta and Pteridophyta in which the union of the 

 sexual cells is effected by the aid of water, the Spermatophyta, which do 

 not separate a motile male gamete, and have the egg-cells permanently 

 enclosed in -the tissues of the parent plant, are forced to adopt other 

 methods. Arrangements to convey the microspores, enclosing the 

 male sexual cell, to the macrospores, enclosed in the macrosporangia 

 and containing the egg-cells, become necessary. 



A large number of Spermatophyta make use of the wind to convey 

 the microspores, i.e. the pollen, to its destination. Examples are all 

 the Conifers, and also the majority of our native deciduous trees such 

 as the Elm, Oak, Beech, Hornbeam, and further our Grasses and 

 cereals. Simple as the relations in this case appear to be, various 



FIG. 525. A, Actinomorphic flower of Geranium sanguineum. B, Zygomorphic flower of Viola 

 tricolor. 0, Asymmetrical flower of Canna indica. 



necessary preliminaries are required for successfully effecting this 

 method of pollination. 



It is especially necessary that such ANEMOPHILOUS plants should 

 produce a very large quantity of pollen, since naturally only a small 

 fraction of what is shed will reach its destination. Thus at the 

 season when our coniferous woods are in flower large quantities of 

 pollen fall to the ground, constituting what is known as sulphur showers. 



Anemophilous plants exhibit some characters in common which 

 stand in definite relation to wind-pollination. The male inflorescence 

 has usually the form of a longer or shorter catkin (Fig. 526) which 

 bears a large number of microsporophylls ; these are so oriented that 

 after the sporangia have opened the pollen can be readily carried away 

 by the wind. Examples are the catkins of the Oak (Fig. 610), Birch 

 (Fig. 604), Alder, Hazel, Hornbeam, and Walnut ; the catkins of the 

 last-named plant (Fig. 602) are especially long. The male flowers of 

 the Coniferae (Fig 510) are similar. The mode of attachment of the 



