INTRODUCTION 19 



vegetative part of the prothallus of the Gymnosperms. 

 The gametophyte or sexual generation in the fern 

 gives rise to the antheridia and archegonia, the 

 fern plant being the sporophyte, or that which we 

 usually term the plant in Angiosperms. In the 

 Angiosperms and Gymnosperms the oosphere awaits 

 fertilisation, and in each case it develops from the 

 prothallium. 



In Angiosperms the pollen-tube may be regarded 

 as representing an antheridium, and the archego- 

 nium, now reduced, consists of the oosphere and 

 synergidse, and is enclosed in the ovule, and this in 

 an ovary. The antipodal cells at the bottom of 

 the embryo-sac may represent a prothallium. They 

 do not contribute to the development of the embryo 

 and disappear. Such in brief are the homologies 

 between the structures of seed-plants and those of 

 so-called non-flowering plants or Cryptogams. 



Reverting to the germination of the male cell or 

 microspore, and the germination and fertilisation ot 

 the female cell or megaspore, the stamens are the 

 male organs and consist of a filament with an anther 

 and anther-cells, which contain pollen-grains. Pollen 

 is variable in size, form, shape, with an inner and 

 an outer coat or intine and extine. Inside the pollen- 

 grain consists of cytoplasm with two large cells, the 

 generative cell and a vegetative cell. If the pollen- 

 grain is placed upon a stigma it develops, and a 

 pollen-tube from the intine grows out of the vege- 

 tative cell. The nucleus of the latter is lost and the 



