77//'; roLLKX-TUBE 99 



The Female Gametophyte.- As is tlic i)r<)(Iii(t of seod-germination, 

 so is the product of sixuv-uvnuiiiatioii a plant. The plant which results 

 from seed-germination, and wliicli ])r()duces spores, has been called a 

 si)orophyte. That which results from spore-germination, and the 

 ultimate function of which is the production of seed; is called a gameto- 

 ])hyte. Hence the mass contained within the embryo-sac is such a 

 l)lant. the female gamctophyte. It will rest in the state in which we 

 now find it until its oiisphere is acted upon by the male element, which 

 wc ha\e yet to consider, and if such action does not occur, it will die 

 and (lisa])pear. 



Connection between Stigma and Ovule. — Between the ovule thus 

 prepared and the stigma, there is an almost continuous connection 

 through conducting tissue, extending through the body of the stigma, 

 style, and placenta. The extent of this conducting tissue, like that of 

 the stigmatic surface, is usually greater or less according to whether 

 there are more or fewer ovules to be fertilized. 



We have seen that the soil u]K)n which the microspore is intended to 

 germinate is the stigma, in angiosperms, and the foramen of the ovule 

 in gymnosperms. The process of germination is dependent upon the 

 following structural characters: 



Structure of the Microspore.^ The ])()llcn-grain consists of a highly 

 hygroscopic mass of tissue, ])artly vital and ])artly nutritive, the latter 

 of variable composition, surrounded !)>■ a thin, iion-])erforated, highly 

 elastic membrane, the Intine, and this in turn by a thicker, non-elastic 

 covering, the Extine, or "Exine," bearing one or more comi)lete per- 

 forations, very thin ])laces, or otherwise modified ])oints u])on its surface. 

 In exce])tional cases there is instead but a single wall. 



Germination of the Microspore. — The ])rocess of fertilization is illus- 

 trated l)\- Fig. 27s, and the onhiiary jjhciionicna are as follows: The 

 l)ollen grain (a), fixed \i\un\ the stigma of the angiosjierm, or upon the 

 sununit of the o\ule of the gymnos])crni, the hygroscoi)ic contents 

 absorb moisture from the secreting or transuding surface with which 

 it is in contact, the nuiss increases in si/e and distends the intine which 

 surrounds it. Shortly ccll-di\ision of its contents takes place, the com- 

 i)ined changes constituting the germination of the micros]>ore. 



The Pollen-tube.— Through one or more of the ])erforations of tlu> 

 extine already existing, or forcii)ly made )>> this ])ro(ess, ])rotrude 

 prolongations of the pollen contents, still cnxcioped in a |)rocess of the 

 intine. Such a i)roIongation is known as a Pollen-tube {h). 



