260 PHYLUM IX. PTERIDOPHYTA 
antherids and archegones. By careful searching young 
fernlets may be found still attached to the gametophytes 
(prothallia). 
(f) 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. 
(h) Where possible compare the structure of the sporangia 
and sori of Marattias (from greenhouses) with those of common 
ferns. 
(t) 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. CampsBe.u, The Structure and Development of Mosses and 
Ferns, New York, 1905. 
N. L. Brirron and AppIsON Brown, Illustrated Flora of the 
Northern States and Canada, Second Edition, New York, 
1913. 
B. L. Roprnson and M. L. Frernaup, Gray’s New Manual of 
Botany, New York, 1908. 
J. K. Smatu, Flora of the Southeastern United States, Second - 
Edition, New York, 1913. 
L. M. UNpERWwoop, Ferns and Fern Allies, New York, 1905. 
