4S4 



BOTANY 



PART II 



All flowers have the function of producing progeny sexually ; the 

 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 efi'ected by 



the aid of water, the Phanero- 

 gams, which do not separate 

 a motile male gamete, and 

 have the egg-cells perman- 

 ently enclosed in the tissues 

 of the parent plant, are forced 

 to adopt other methods. 

 Arrangements to convey the 

 microspores, enclosing the 



Fio. 450. — Cymose inflorescence (dichasinm) of Cerastium 

 collinum t-t"", successive axes. (After Duchartre.) 



Pig. 451. — Scorpioid cyme ot Sympliytum 

 asperriimnn. (After Duchartre.) 



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

 and containing the egg-cells, become necessary. 



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

 the micro.spores, 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 

 necessary preliminaries are required for successfully effecting this method 

 of pollination. 



It is especially neces.sary that such anemophilous plants should }iroduce a very 

 large rjuantity of pollen, since naturally only a small fraction of what is shed Avill 

 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. When sucli forests stand in the vicinity of lakes or of the sea-coast the 

 l)ollen thus shed jnay form an essential part of the food of the a(]uatic fauna. 



Anemophilous plants exhiliit some cliaracters in common which stand in 

 definite relation to wind-pollination. The male inflorescence has usually the form 

 of a longer or shorter catkin which bears a large number of micro-sporophylls ; these 



