48 Knud Jessen. 



can withstand being carried a long distance in salt water 

 without getting damaged. Fig. 21, F shows a transverse 

 section through a ripe fruit. In the wall, within a few layers 

 of cells which keep alive a long time, there occurs a consider- 

 able area of dead cells containing air. The shaded part is 

 sclerenchymatous. I have found no difference in the degree 

 of development of this floating tissue in the fruit of var. 

 Egedii which Porsild gathered on the strand on Disco and 

 in the fruit of a specimen of the typical form which had been 

 growing in Denmark at a distance from the sea. 



Pot. anserina is almost cosmopolitan; for further notes 

 regarding its distribution the reader is referred to Wolf. 



The alcohol material is from Greenland and Denmark. 



Sylvén has observed the germination during spring in 

 nature. During the second year the slightly branched pri- 

 mary root was found to be about 3 mm. thick and spindle- 

 shaped; sometimes, however, it is rather weak and then an 

 adventitious root takes on its function. In older plants 

 the primary root is absent. 



The short, vertical rhizome is monopodial and the annual 

 growth-increment hardly lives more than one year; the leaves 

 die away every autumn and the shoot-apices are protected 

 by scale-leaves. The rosette-leaves subtend from one to 

 several runners, which may attain a length of about one 

 metre; but the longest runner I have seen from Greenland 

 was only about 14 metre long. According to Warming, 

 who mentions Pot. anserina in his paper of 1884, these sym- 

 podial runners are to be compared with the lateral floral- 

 shoots in Pot. erecta (L.) Dalla Torre. The single shoot-gene- 

 rations consist normally of a long and a quite short inter- 

 node, after which they terminate in a flower. At the base 

 of the flower-stalk are two small connate bracts of which 

 the lower subtends an assimilatory shoot which has leaves 

 in a rosette and as a rule soon produces 1 — 2 strong adven- 



