Rosaceæ. 77 



which is situated just outside the endodermis, the radial 

 walls appearing as thick, refractive, non-stratified cushions 

 (Fig. 30, E). Also in roots of the first order a similar struc- 

 ture has been found, but it is less common there. The peri- 

 derm is formed during the first period of grovsi-h in the outer- 

 most layer of the pericycle at the same time as the primary 

 cortex dies. 



The stem is covered with a fairly dense layer of uni- 

 cellular, thick-walled hairs; sometimes a few weak spines 

 occur. The axis-system in this species illustrates fairly well 

 how highly the development of the different tissues is de- 

 pendent on the length of life and the function of the different 

 parts of the stem. In the erect part of the stem no periderm 

 occurs, with the exception, however, of the lower scale-leaf- 

 bearing part which as already mentioned becomes at any 

 rate partially perennial. In the first year it consists here 

 of only about three layers, which develop immediately out- 

 side the bast in the cortex as is the case in the species 

 of various other groups of Rubi investigated by Frits сн 

 (1, с). In the stolon the same features occur as in the stem 

 of Rub. arcticus; a phellogen is developed which probably 

 does not become functional. On the other hand, in the some- 

 what thickened apex of the stolon a fairly well-developed 

 periderm is found towards the end of summer, in correlation 

 with the altered conditions. In Denmark it consists chiefly 

 of phelloid cells which at that time when the bud begins to 

 become independent, contain a large quantity of starch. 

 Also in the perennial subterranean axis the periderm, which 

 is 10 — 15 layers thick, consists chiefly of phelloid, at any 

 rate in Denmark in humus soil, while the periderm in the 

 Iceland specimens was richer in cork. The periderm rich in 

 phelloid makes a spacious reservoir of food-material. It con- 

 tains small intercellular spaces. I have seen no endodermis 

 either in the rhizome or in the aerial stem. 



