n6 FERNS THE ANCESTORS OF FLOWERS 



place in the Gingko and the Cycads as occurs in the 

 detached, separately growing sexual generation or " pro- 

 thallus " of the fern. 



These remarkable survivals of the fern-stage of develop- 

 ment are suppressed in the modern " flowering plants," the 

 pine trees and the whole host of trees and herbs which bear 

 "flowers." In them there are no "sperms," but the pollen- 

 spore gives rise, when carried to the carpels or female 

 leaves, to a minute hair-like filament, almost devoid of 

 structure. The pollen filament, thus growing, penetrates the 

 tissues surrounding the equivalent of the egg-bearing "pro- 

 thallus," which is never shed, but remains fixed to the female 

 leaf on which it originated. Thus the ovule or egg-cell is 

 "fertilised," so to speak "in place," by the pollen filament 

 itself without the production of any separate "sperms." The 

 sexual or "prothallus" generation of the fern is in fact 

 reduced and becomes, so far as the female is concerned, a 

 minute part of the large spore-bearing plant or first gene- 

 ration, whilst so far as the male spore (pollen) is concerned, 

 it is detached as in ferns, but never develops further than 

 the condition of a tiny filament, and never produces sperms. 

 No one would ever guess that such a history lay behind 

 the pollen and the seed of our common plants on first 

 acquaintance with them. The discovery was one of the 

 many great triumphs of scientific investigation in the 

 second half of "the wonderful century" which closed ten 

 years ago. 



The fertilised ovule or egg-cell of the flowering plant is 

 contained in an envelope and packing of more or less 

 numerous " coats." It swells up when fertilised and com- 

 mences to grow within its case as a young plant, and is 

 said to be a ripe and fully-formed " seed " when its envelope 

 becomes hard and protective. The formation of what is 

 properly called " seed " is a protective process in which the 

 young embryo, already well advanced in growth, is en- 



