44 



Knud Jessen. 



cork each separated from the other by a layer of phelloid. 

 In this species also, intercellular spaces are absent from the 

 inner side of the cork-layers. 



Fig. 17 shows a portion of the transverse section of a 

 floral shoot which may serve as an example of the stem- 

 structure of the monopodial Potentillas mentioned in the pre- 

 sent work. The vascular bundles may vary somewhat in 

 number in the different species. The primary groups of 

 vessels always remain distinct: the function of the cambium 

 is slight. The pericycle is transformed into a rather strong 

 bast-ring, about 3 — 6 layers thick. No distinct endodermis 



is present. The structure of the cor- 

 tex is similar to that described for 

 Pot. pulchella. 



The leaves are almost glabrous 

 or slightly hairy upon the upper 

 Fig. 17. Potentilla maculata. surface, and upon the lower surface 



Portion of a transverse section of 



a norai shoot (about »/,); b, bast; the hairs are sparsely scattered. Ihe 

 : TZÏ JTS '•::■ A hairs ™ projecting. Lance maintain* 

 what disorganized ; x, xyiem. thatPo^Friesea/iaLge.isdistinguished 

 from Pot. maculata Pour, among other things by the fact of the 

 leaves being glandular, but Abromeit states that in Sweden he 

 has found numerous yellow glands upon the lower surface of 

 the leaves of the latter species. In the key given by Wolf of 

 the determination of the forms of Pot. maculata, among the 

 northern forms leaf-glands are assigned only to Pot. Frieseana 

 (found only on Disco). I have, however, usually found numerous 

 short-stalked glands on both leaf-surfaces of Pot. maculata from 

 the majority of the localities represented in the Arctic her- 

 barium in Copenhagen. The glandular hairs occur in unequal 

 quantities in different plants and on the different leaves 

 of the same plant; upon the upper surface they often occur 

 especially in the furrows above the larger bundles. The form 

 of the glands is shown in Fig. 18, D. 



