IOWA ACADEMY OP SCIENCES. 159 



EXPLANATION OF PLATE VI. 



In all figui-es the same letter is used for the same character — c, cuticle; 

 e, epidei'mis; st, stereome: m, mestome; c b p, chlorophyll bearing paren- 

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

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

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



Figures I, 



A COMPARATIVE STUDY OF THE SPORES OF NORTH 

 AMERICAN FERNS. 



BY C. B. WEAVER. 



Perns 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 knowledge concerning the spore characters of the 

 different genera and species of North American ferns. 



The measurements of a few spores are here given: 



