108 Knud Jessen. 



thickness (about 190/i) and the thickness of the palisade-tissue 

 is about f . Below the stomata of the upper surface air-spaces 

 are produced in the same manner as described for Sibbaldia 

 procumbens (p. 58). The spongy parenchyma is rather loose in 

 structure and contains, as shown in Fig. 40, D, besides large 

 intercellular spaces numerous very small ones. The cells are 

 branched. 



The leaf-teeth contain a slightly developed epithema; 

 the water-pores occur on a limited space upon the upper 

 surface; these structures have been mentioned by Reinke 1 . 



The structure of the leaf-stalk is as in A. færøensis 

 and A. alpina (see Fig. 39, F). 



Murbeck has demonstrated parthenogeny in A. minor, 

 which produces only a very small quantity of imperfect 

 pollen. — In the flowers of A. glomerulans from Greenland a 

 great many of the anthers had fallen off; in those which were 

 still attached I found no fully developed pollen. 



The flowers of A. vulgaris, which in structure almost 

 agree with those of A. alpina, have been described and figured 

 by H. Müller 1873 2 and 1881 (I. c). 



Sorbus americana Willd. 

 Lit. Warming, 1887. Rosenvinge, 1896. 



The alcohol material is from Ivigtut in Greenland. 



This Sorbus which bears much resemblance to S. aucu- 

 paria is a small tree with an erect, straight growth; it does 

 not branch much, but several stems may proceed from the 

 same root. The largest trees hitherto found in Greenland 

 measured about 4 metres in height and the stems were about 

 9 cm. thick. These trees were 56 years old (Rosenvinge). 

 Generally, however, it is lower in growth. It occurs in south- 



1 Secretionsorg. Pringsheim Jahrb. Bd. X. 1876. 



2 Die Befruchtung der Blumen durch Insekten. Leipzig. 



