T. Holm — Erigenia halbosa. 69 



Several ducts, rhombic in transverse sections, occur inside the 

 endodermis as a peripheral band around the central-cylinder. 

 The increase in thickness, at this part of the seedling-tuber, is 

 then due not only to the pericambium, which has now devel- 

 oped a broad parenchyma, a secondary bark, but also to the 

 formation of a cambium between the leptome and hadrome. 

 The tuber as it appears during the seedling-stage is thus to be 

 considered as a swollen part of the primary root, of which the 

 structure has been modified somewhat by the divisions of the 

 pericambium and by the formation of cambial strata. The 

 divisions of the pericambium have not, however, ceased at this 

 moment, but continue during the further growth of the tuber- 

 ous root-part. If we, for instance, examine another specimen 

 in its third year, we notice that the epidermis, the cortex and 

 endodermis have been thrown off, while the pericambium, by 

 outward divisions has begun to develop a number of cork- 

 layers at the same time as it continues the formation inwards 

 of secondary cortex. 



While thus the anatomical structure of the primary root is 

 readily recognized as that of a true root in its entire length, in 

 its tuberous and in its filiform part, and well comparable with 

 that of a specimen in its third year, we find in fully matured 

 specimens, such as have reached the flowering stage, a very 

 different structure, which may have led to the belief that the 

 so-called " globular tuber " is a stem and not a root ; that is 

 supposing a study of the seedling-stage to have been omitted. 

 The mature tuberous root possesses a number of cork-layers, a 

 secondary bark of very considerable width, filled with starch, 

 and inside the bark is a band of collateral mestome-bundles 

 with cambium between the leptome and hadrome and besides 

 well defined strata of interfascicular cambium, while a broad 

 •pith occupies the central portion of the root, of which, how- 

 ever, the innermost part is broken down into a cavity ; thus the 

 principal features of the primary root are, almost, totally 

 obliterated. Oil-ducts are quite numerous in the mature root ; 

 they are located in the same radii as the mestome-bundles and 

 occur in four or five concentric bands. The innermost oil- 

 ducts are to be seen in the leptome itself, the others some dis- 

 tance apart, the outermost being very near the periphery, 

 though not in contact with the cork. It appears as if the 

 ducts of the outermost two bands are mostly pentagonal in 

 transverse sections, while those of the inner are rhombic and 

 somewhat narrower in circumference. 



Having thus described the root-system of Erigenia, we 

 might, also, give a few notes on the structure of the other 

 organs, as these are developed in the seedling and the mature 

 plant. The petiole of the cotyledon exhibits the same pecu- 



