258 Eue. Warming. 



and, according to Porsild, far from present and former 

 settlements, and in other places for instance together with 

 Ranunculus hyperboreus. 



It is a hapaxanthic, summer-or winter-annual 

 species, and does not appear to deviate from this rule in 

 Arctic countries. The fullest account of it has been given by 

 Wittrock (1908). According to him, in Central Sweden, the 

 winter-annuals may begin to flower even during the autumn; 

 they continue flowering in the milder period of the winter 

 and bring it to a termination in the spring, with an abundant 

 seed-production. There, the winter-annuals are the most 

 vigorous, owing to the fact that numerous adventitious roots 

 are developed during the autumn, on account of the increased 

 dampness of the soil. Wittrock's figure shows that the 

 adventitious roots proceed from the leaf-axils, and that they 

 may branch freely. A very distinct account of these con- 

 ditions is given by Korsmo (Fig. in his valuable work 

 "Ugræsplancher"). If the branches have been detached from 

 the parent-stems, in some way or other, vegetative propaga- 

 tion may thereby take place. In such a case it may perhaps 

 also become pollacanthic, as an observation made by Bon- 

 nier also seems to indicate. 



Other species also, in addition to being pollacanthic, are 

 sometimes described as hapaxanthic, for instance Sagina 

 procumbens and Sagina Linnaei. It is not improbable that 

 this may be the case. 



II. Leaf Anatomy. 



With regard to the anatomical structure of the Arctic 

 leaves the reader is more particularly referred to Bonnier 

 and Borgesen, and in "Meddelelser om Grönland", vols. 36 

 and 37, to a series of treatises by Henning E. Petersen, 



