A KEY TO THE BRITISH SPHAGNA 
31:3 
ft St. Is. larger, 1-2 mm. long. 
a . Cortical cells in section ellip¬ 
tical and strongly incrassate. 8. iiercynicum Warnst. 
b'. Cortical cells subcircular with 
thin walls. 
a". St. Is. with large auricles. S. auriculatum Schimp. 
b" . St. Is. without or with minute 
auricles. 
St. Is. 1—1*3 long, fibrillose 
above the middle . 8. inundatum Buss. 
St. Is. 1*4-2 mm. long, fibril- 
lose below the middle ... 8. aquatile Warnst. 
## 13r. Is. multiporose on the upper 
surface . 8. crassieladum Warnst. 
b. Br. Is. with numerous true pores on 
both surfaces. 
Br. 1 s. on outer surface with pores 
arranged in a continuous 
series . S. rufescens Nees & Hornsch. 
Br. Is. on outer surface with pores 
arranged in an interrupted 
series. 8. turgidulum Warnst. 
In order to examine the pore-structure of the stem cortex and 
of the branch leaves it is necessary to use a stain ; methyl-blue gives 
the best result for this purpose. In ascertaining whether the pores 
are on the upper or lower surface of the leaf, a high power must be 
used, care in focussing is necessary, as the pores on the opposite 
surface may show through. 
Group Cymbifolia. 
A. Chlor. ceils of the br. Is. free on the upper 
or on both surfaces. 
I. Chlor. cells equilateral to shortly isosceles- 
triangular, not reaching the lower sur¬ 
face . 
II. Chlor. cells spindle-shaped, isosceles-tri¬ 
angular to trapezoid, reaching both 
surfaces. 
a. Chlor. cells much thickened on upper 
wall. 
Chlor. cells narrow up to 10 y, wide. 
Chlor. cells wider up to 18 y wide. 
b. Chlor. cells not thickened on the upper 
wall. 
Chlor. cells papillose. 8. lialclcodense Warnst. & Card. 
Chlor. cells not papillose . 8. cymbifolium Ehrh. 
B. Chlor. cells completely enclosed by the 
hyaline cells on both surfaces of the leaf... S. medium Limpr. 
Journal of Botany. — Vol. 61. [December, 1923.] 2 a 
8. imbricatum Buss. 
8. subbicolor Hampe. 
8. papillosicm Lindb. 
