34 Knud Jessen. 



depository tissues of the rhizome, and, in addition, large 

 sphaero-crystals. The shoot may attain a considerable age. 

 In the oldest part of the shoot in my material about 15 

 partially indistinct annual rings could be counted with an 

 average breadth of about 40 ц. Even at this age the rhi- 

 zome is closely covered with dead fragments of leaves. An 

 endodermis is present. 



In the flowering stem there is no distinct endodermis. 

 Outside the vascular bundles, about 10 in number and sepa- 

 rated by broad medullary rays, there is a ring of stereom 

 consisting of 3 — 7 layers of slightly lignified bast. The outer 

 part of the medullary rays also becomes woody. The struc- 

 ture of the cortex is similar to that of Pot. pulchella. The 

 epidermis consists of rather small cells; the tangential walls 

 are about 6.5// thick. The pith is homogeneous. 



The leaf is hairy on both surfaces, but more so upon 

 the lower (Fig. 13, A), where there also occurs a fair number 

 of glandular hairs of the type figured (Fig. 13, E); the stalk 

 is 2 — 4 celled. Besides in the alcohol material, fairly large 

 numbers of glandular hairs are shown also on leaves from 

 Ellesmereland (determ. Simmons) and from King Point in 

 Arctic America (determ. Ostenfeld), contained in the her- 

 barium of the Botanical Museum in Copenhagen; (see Pot. 

 nivea p. 31). The glandular hairs may also occur upon the 

 upper surface of the leaf along the margin. 



The outer wall of the upper epidermis is about 2.5/^ 

 thick; the inner wall is not mucilaginous. The radial walls 

 of the upper epidermis are almost straight (Fig. 13, C), of 

 the lower undulating. Stomata occur only upon the lower 

 surface, and as seen in the figure, they often project some- 

 what, a fact which should doubtless be correlated with the 

 dense hairy covering (compare Pot. pulchella and Pot. nivea). 

 There are two layers of coarse palisade-cells and a rather 

 loose spongy parenchyma the cells of which are slightly 



