76 Knud Jessen. 



erect lower portion like the floral shoot and then creeping 

 runners. The runners have elongated internodes, small leaves,, 

 and develop no roots; from the leaf-axils other runners arise. 

 Towards the end of summer the apex of the stolon slightly 

 penetrates the ground; it then becomes negatively geotropic, 

 the internodes shorten and scale-leaves are developed. The 

 stolon is somewhat thickened at the point where it bends and 

 thence long, vigorous and richly branching roots arise (Fig. 29, B). 

 These shoots also pass the winter at the surface of the ground. 

 According to Warming (1884) the stolons may attain a length 

 of 134 — 2 metres. In Arctic Norway they are, according to 

 Norman, often above 2 metres, and he places the maximum 

 at about 4 metres. During autumn the aerial shoots die 

 away, at any rate partially, and the terminal buds of the 

 stolons are set free and become independent individuals. 



The structure of the shoot in Rub. saxatilis may be pro- 

 duced through a slight modification of the type common 

 among the Eiibatus. As the stolons live through one sum- 

 mer only, the flower-buds are placed near the surface of the 

 ground, and new shoots arise from the base of the floral 

 shoots as well as from the wandering shoots. Moreover, e. g. 

 in Denmark, specimens are met with which form a transition 

 between the two types, as they enter the winter with living 

 shoot-bases, a few cm. long, which protrude above the ground 

 and bear flower-buds. 



Anatomy. Of roots only those adventitious roots 

 have been investigated which arise from the apex of the 

 stolons. The epidermis in the roots of the first order is thin- 

 walled, while the subepidermal layer has stronger, brown 

 walls. In the roots of the second order the epidermis has 

 thicker outer walls, and the exodermis is not so well-marked. 

 The central cylinder is in the former tetrarch and in the 

 latter diarch. The roots of the second order are particularly 

 characteristic owing to the structure of the cortical layer 



