170 



EVOLUTION OF PLANTS 



pollen-spores produced is enormously in excess of the 

 macrospores. Indeed, so abundant is the pollen, that 

 the ground in the neighborhood of the trees is some- 





FIG. 42 (Coniferae). A, branch of a pine (Pinus contorta) with male 

 flowers,.//; B, longitudinal section of a single flower, showing the 

 arrangement of the sporophylls; C, a single sporophyll, showing the 

 two microsporangia, mi, upon its lower surface ; D, a section through 

 the microsporaugium ; E, a single microspore, showing the antheridium, 

 an, and the vesicular outgrowths of the wall, v, which serve as sails; 

 F, a female flower of the same pine; G, a single sporophyll from the 

 female flower, showing the small scale, sc, by which it is subtended ; H, 

 a sporophyll from an older cone, showing two macrosporangia (ovules), 

 ma, upon its inner face; I, longitudinal section of an ovule (macro- 

 sporangium) ; the large macrospore contains the gametophyte, g, 

 bearing several archegonia, or ; p, a pollen-spore sending down the tube 

 by which the archegonia are fertilized ; J, a young embryo ; sus, sus- 

 pensor ; x, apical cell ; K, section of a ripe seed, containing the embryo, 

 em, imbedded in the prothallial tissue, g ; L, young sporophyte, show- 

 ing the cotyledons, cot ; stem, st ; root, r ; s, the empty seed-coat. 



times covered with a layer of the sulphur-colored 

 powder. 



The germination of the pollen-spores and the fertili- 

 zation of the archegonium are effected as in Taxus. As 

 in that genus, no trace of motile spermatozoids has yet 



