140 Plant Biology 



Microsporophy]] 



-Microsporanqium Microspore 



c n 



D 



Jnbequment 



.^ ^ \ Mecjaspore 



^^■^—Mlcrosporan^ia 



/Aegaqamebophybe 

 Micropyle / 



; 



I ^Alecjasporan(j]um 

 yyieaasporophyll 



i 



Meaaaamebophybe 

 hbQCjumenb 



J 



Cotyledons 

 Food 



Ovule 



Root 



seed "coats 



''PoVenqrairy yArchegomum 

 ^ y MQqasporanqium 



.L._i ^rcheqomum 



"/ 







yy PoUen cjfrain and tube 



Fig. 52. — Pine tree life cycle (Pinus sp.). A, Branch with (male) staminate 

 cones; B, staminate cone enlarged with upper right section showing microsporo- 

 phylls, microsporangia, and microspores; C, microsporophyll enlarged (side view) 

 showing microsporangium and microspores; D, microsporophyll enlarged and 

 viewed from below; E, microgametophyte (pollen grain) developed from a micro- 

 spore; F, developing microgametophyte with its pollen tube and nuclei; G, branch 

 with (female) carpellate cone; H, carpellate cone enlarged with upper right sec- 

 tion showing megasporophylls, megasporangia, and megaspores; I, megasporophyll 

 enlarged (side view) showing megasporangium and megaspore; J, megasporo- 

 phyll enlarged and viewed from above; K, megasporophyll still more enlarged 

 (side view), showing megasporangium, integument, megagametophyte, and micro- 

 pyle; L, entrance of microgametophyte (pollen grain) into the megasporangium 

 through the micropyle. Note the megagametophyte with its archegonia, each con- 

 taining a megagamete (egg) ; M, as L above, with pollen tube growing toward 

 archegonium; A^, fusion of the contents of the microgametophyte (pollen grain) 

 and the megagamete (egg) of the archegonium; O, mature pine seed (longitudinal 

 section) with two seed coats and food; P, germination of seed (split) showing 

 cotyledons and root. This young plant is an immature sporophyte which even- 

 tually will develop into a pine tree. 



