THE BRACKEN FERN 105 



gametes are borne close together on the same plant, it is probable that 

 as a rule self-fertilization the union of an egg with an antherozoid 

 produced by the same plant does not occur in the fern. That it 

 does not is suggested by the fact that the antherids usually ripen and 

 discharge their antherozoids before the 

 archegones on the same plant are 

 mature. This would seem to make 

 cross-fertilization necessary that is, 

 the union of an egg and an antherozoid 

 borne by different plants. On the other 

 hand, young antherids are sometimes 

 found on the same plants with well- 

 developed archegones, and it is quite 

 possible that self-fertilization occurs 

 now and then. Cross-fertilization is 



made easier by the fact that sexual FIG. 57. A fern anthero- 

 plants commonly grow in groups, be- zoid. From a preparation by 

 cause many spores were dropped and Dr. W. N. Steil. 

 germinated near one another. Since 



these little plants grow in moist places, there is enough water present 

 much of the time on their lower surfaces so that the antherids can open 

 and the antherozoids can swim to the mouths of the archegones either 

 on the same or on neighboring plants. 



132. Development of the Asexual Plant. Doubtless it 

 often happens that more than one egg is fertilized and so that 

 more than one zygote is formed in the archegones of a single 

 plant ; but we seldom find that more than one zygote has 

 developed into a plant of the next generation. This is prob- 

 ably because the new plant growing from the zygote receives 

 food for some time from the sexual plant that bore the egg ; 

 since the sexual plant is small and can supply only a limited 

 amount of food, only that one embryo develops which has an 

 advantage because of its greater vigor or its better location ; 

 the less fortunate embryos are starved and cease to grow. 



The zygote, like the zygote of the moss, germinates in the arche- 

 gone. Very early the embryo (the young asexual plant, Figure 58) de- 

 velops four parts : one of these, the foot, remains small and imbedded 

 in the tissues of the sexual plant, from which it absorbs food for the 

 use of the embryo. Two other parts of the embryo, the primary root 



