MODES OF REPRODUCTION IN PLANTS. 



163 



Fig. 7 shows a prothallus seen from the under side and much magnified ; 

 h, are the root-hairs ; an, antheridia ; and ar, archegonia. The an- 

 theridia produce cork-screw coiled antherozoids which pass to the 

 archegonia and fertilize their germ-cells. The second generation de- 



f IG. G. 



af 





Fig. 5. 



Fig. 7. 



velops from the germ-cell, as shown in Fig. 8. By a further growth of 

 stem and fronds, the well-known state of the fern is jiroduced. The 

 spores are borne on the under side or edges of the fronds. In some 

 species the spores are formed only on a portion of the fronds, the 

 others being sterile. The plant commonly known as the fern does 

 not have any male or female parts, and may live for many years, pro- 

 ducing countless spores. The sexes are confined to the minute scale, 

 which is so small as to pass unnoticed, and if seen would not suggest 

 its origin or destiny. Dr. Farlow has discovered instances where the 

 pi'othallia produced fern-plants without the usual process of fertiliza- 

 tion. These are only the exceptions which prove the rule. 



There is a little group of ferns to which the "adder-tongue" be- 

 longs, that has the prothallus underground, consisting of an irregular 



