260 PHYLUM IX. PTEEIDOPHYTA 



antherids and archegones. By careful searching young 

 fernlets may be found still attached to the gametophytes 

 (prothallia). 



(/) If possible secure specimens of Adder-tongue, and com- 

 pare the structure of the sporangia with the foregoing. 



(g) Search the borders of lakes, ponds, and slow streams for 

 Marsilias. They may probably be found in every part of 

 the country, although they are rarely collected. 



(A) Where possible compare the structure of the sporangia 

 and sori of Marattias (from greenhouses) with those of common 

 ferns. 



(i) In some places it is possible to secure sporophytes of 

 Isoetes for a comparative study. 



(j) Try to secure fresh spores of Isoetes or Marsilia for a 

 study of heterospores, and of the antheridial, and archegonial 

 gametophytes. 



LITERATURE OF PTERIDOPHYTA 



D. H. Campbell, The Structure and Development of Mosses and 



Ferns, New York, 1905. 

 N. L. Bbitton and Addison Brown, Illustrated Flora of the 



Northern States and Canada, Second Edition, New York, 



1913. 

 B. L. Robinson and M. L. Fernald, Oray's New Manual of 



Botany, New York, 1908. 

 J. K. Small, Flora of the Southeastern United States, Second 



Edition, New York, 1913. 

 L. M. Underwood, Ferns and Fern Allies, New York, 1905. 



