1896. Root-Tubers of Isopyrum occidentale. 281 
in such manner that the xylem bundles are separated and a 
comparatively large central mass of parenchyma is formed. 
A cylindrical mass of the cells in the central portion of this 
tissue, extending the length of the tuber only, undergoes 
sclerosis to such an extent that the cell-lumina are almost ob- 
literated, and the walls are simply pitted. These sclerotic 
cells are cylindrical in outline, are joined transversely at the 
ends, and their length is several times their diameter. 
A small bundle of secondary xylem is formed from each of 
the meristematic arches lying between the primary bundles. 
The larger part of the bulk of the tuber is due to the greatly 
accelerated development of the pericycle, resulting in the 
formation of a thick concentric ring of parenchymatous tissue, 
retaining in greater part its meris- 
tematic character, and differs from 
tumbers of small intercellular spaces. 
Extending to an indefinite distance 
from each primary bundle is a wedge 
shaped cambium ray. Near the cor- 
tex in the same plane as the rays 
aésmall bundles of elongated cells, 
Which finally become woody, which 
have originated independently in the 
. istances is due to the exaggerated development of ve 
» and that the process in the first is accompan! 
: . Nat. VI. 
2: echerches sur l'appareil tegumentaire des racines. Ann. 4. Sc 
‘ i. Nat. VI. 20: 
7 Recherches sur la structure des Ranonculacees. Ann. d. Sci. Na 
