105 
very high degree, if it had intercellular spaces which were not 
protected. In regard to leaves which persist for several years, 
it may be said that the 
degree of protection is with- 
out doubt in proportion to 
the size of the air-cavity. 
To what degree the air-cavity 
and the large intercellular 
spaces serve to utilize the 
oxygen formed by assimila- 
tion of the carbonic acid 
formed by respiration I am 
not able to say. The leaf 
is also protected by different 
kinds of hairs (cf., e. g., 
Warning, Biol. Optegnelser, 
p. 53). 
JunGner's! theories re- 
garding the importance of 
the form of the leaf may Fig. 21. Cassiope tetragona. 
doubtless be regarded as Stem. x 180. (Phot.) 
extremely fanciful. 
Cassiope hypnoides (L.) Don. (Fig. 22.) 
Börsesen, 1895, pp.236—237. Tepin, 1892, p. 75. Hesser- 
Man, 1900, p. 27. 
The specimens I have had for investigation are from the 
following localities: — West Greenland: tent 16 (July 28, 1887, 
C. Ryder); loc. ign. (Aug. 1, 1892). East Greenland: Dronning 
Louises Ø (Aug. 8, 1885, Eberlin). [Sweden: Areskutan (Aug. 12, 
1890).] 
This species belongs to that group of the Cassiope 
7 Junener, Klima und Blatt in der regio alpina. Flora, Bd. 79, 1894, p. 219. 
