IOWA ACADEMY OF SCIENCES. 159 



EXPLANATION OF PLATE VI. 



In all figures the same letter is used for the same character — c, cuticle; 

 e, epidermis; st, stereome; m, mestome; c b p, chloi^ophyll bearing paren- 

 ■chyma; b, bulliform cells; mes, mesophyll; h, hadrome; 1, leptome; c p, 

 oonical projections. All figures drawn with camera to the same scale. 

 General drawings i inch objective; detailed drawings ^ inch objective. 



Figures I, II, III, Sporobolus heterokpis. 

 ' ' vaginxHorus. 



" Hookeri. 



" cryptandrus. 



Panicum proliferum. 

 " capillare. 

 " Crus-galli. 



A COMPARATIVE STUDY OF THE SPORES OP NORTH 

 AMERICAN FERNS. 



BY C. B. WEAVER. 



Ferns have been objects of interest to botanists and culti- 

 vators; they have therefore been studied more than many of 

 the flowering plants. Their simple structure and the apparently 

 well defined limitation of species has rendered them easier for 

 purposes of study than many of the groups of Phaenogams. 



The purpose of this paper is to make a small contribution 

 toward our kaowledge concerning the spore characters of the 

 different genera and species of North American ferns. 



The measurements of a few spores are here given: 



