Page:Popular Science Monthly Volume 25.djvu/173

Rh Fig. 7 shows a prothallus seen from the under side and much magnified; h, are the root-hairs; an, antheridia; and ar, archegonia. The antheridia produce cork-screw coiled antherozoids which pass to the archegonia and fertilize their germ-cells. The second generation develops



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 produced. 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, producing 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 prothallia produced fern-plants without the usual process of fertilization. These are only the exceptions which prove the rule.

There is a little group of ferns to which the "adder-tongue" belongs, that has the prothallus underground, consisting of an irregular