38 Knud Jessen. 



lignified medullary rays are gradually formed, similar to 

 those which are found in the primary root, of which they 

 may constitute the main portion. The rays of wood contain 

 much parenchyma. The periderm consists of alternating 

 layers of cork-cells and phelloid-cells; in the former the walls 

 of the lateral roots are specially strong. The intercellular 

 spaces are fairly large in the periderm; they are absent from 

 the inner side of the cork-layers. The outer part of the se- 

 condary cortex becomes gradually compressed owing to 

 growth in thickness. The primary root which, as already 

 mentioned, may attain a thickness of at least 6 mm. is doubt- 

 less the chief depository of food-material. 



The rhizome is similar in structure to that of Pot. piil- 

 chella. In the periderm 1 — 2 layers of phelloid-cells alter- 

 nate with a layer of cork-cells. The intercellular spaces are 

 rather large; they are absent from the inner side of the cork- 

 layers. The rhizome may attain an age of at least aboutlö years. 



The material at my disposal allowed an investigation of 

 the amount of the food-materials — starch and fat — con- 

 tained in the rhizome in the months of May, June, July 

 and September, with the following result: — 



17. V 4. VI medio. VII 14. IX 



(Cf. Pot. nivea). Though the rhizomes investigated were 

 collected in different localities and in different years yet the 

 investigation is of some interest particularly as regards this 

 plant which is hardly green during winter. Plants from the 

 second column were collected on June 4, and the leaves were 

 not unfolded; consequently, the very decided increase in the 

 amount of the starch as compared with the plants in the first 

 column cannot be due to new acquisition, but must have 

 been produced by the transformation of other materials which 



