164 



THE POPULAR SCIENCE MONTHLY. 



mass of colorless cells, which may not exceed one twenty-fifth of an 

 inch in diameter. This group forms another. step toward a greater 



simplicity of the sexual generation in plants. The 

 spores of the Ojihioglossacece are developed less 

 superficially on the fronds than in the lower or- 

 ders of ferns. This is a morphological point 

 which is worthy of mention here. The whole 

 structure of the asexual generation is more highly 

 developed than in other ferns, while the sexual 

 generation is much reduced and simplified. 



The J^quisetacece, or horse-tails, form a small 

 group of flowerless plants, with hollow, jointed 

 stems and cone-like spore-heads (Fig. 9). The 

 scouring-rush, with its rough, grooved stem, is a 

 leading member of this family. The prothallia 

 are small and irregularly branched, and in most 

 species the male and female parts are on sepa- 

 rate plants (dioecious). The antheridia-bearing 

 prothallia are much smaller than the female, the 

 latter being sometimes half an inch in length. 

 The structure of the male and female organs is 



Fig. 8. 



Fig. 9. 



Fig. 10. 



much the same as in ferns. The antherozoids are larger, and the 

 archegonia are more deeply situated in the prothallus. The conspicu' 



