110 ELEMENTARY STUDIES IN BOTANY 



(which contain the eggs) ; a microsporophyll bears one or 

 more microsporangia, which contain microspores ; and when 

 microspores germinate, they produce male gametophytes, 

 that is, gametophytes that bear only antheridia (which 

 contain the sperms). 



It may help to remember what heterospory involves in the 

 life-history of a plant by giving the formula of the life-history 

 of a heterosporous plant, which of course must include two 

 gametophytes. The sexual cells (egg and sperm) are indi- 

 cated by the conventional sex signs ( ? is for female, and $ for 

 male), and the two kinds of spores are indicated by their 

 relative size. 



G-9 x 



,*>- 

 G <? 



S 



Among the Seed-plants it often happens that the mega- 

 spores and microspores are borne on different sporophytes, 

 so that in such life-histories two sporophytes must be in- 

 cluded, as well as two gametophytes. Two sporophytes 

 would need two eggs, so that the formula becomes somewhat 

 complicated, but it gives some appreciation of the machinery 

 of' the higher plants. 



CN>3. Gametophytes. In 59 (p. 98) the gametophyte of a 

 fernN^vas described, which may stand in a general way for the 

 gametophytes of most Pteridophytes, for most Pteridophytes 

 are homosporous. These gametophytes are alike in usually 

 bearing both sex-organs, therefore they are not male or female, 

 but both ; and also they are quite independent of the sporo- 

 phyte which produced them by means of its spores. 



But in heterosporous plants there are two kinds of game- 

 tophytes, and these must be described if one is to understand 

 seeds when they appear. 



When a microspore germinates, there appears within it 

 a small group of cells, but the group never grows so as to 



