IOWA. ACADEMY OP SCIENCES. 
159 
EXPLANATION OP PLATE VI. 
In all fig-ures the same letter is used for the same character — c, cuticle; 
e, epidermis; 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 ^ inch objective. 
Pigures I, II, III, Sporoholus heterolepis. 
“ IV, V, “ vaginseilorus. 
‘‘ VI, “ Hookeri. 
VII, VIII, “ cryptandrus. 
“ IX, X, Panicum proliferum. 
“ XI, XII, “ capillare. 
“ XIII, XIV, “ Crus-gallL 
A COMPAKATIVE STUDY OP THE SPORES OP NORTH 
AMERICAN PERNS. 
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 kuowledge concerning the spore characters of the 
different genera and species of North American ferns. 
The measurements of a few spores are here given: 
