AMERICAN MIDLAND NATURALIST. y 131 
with no indication of increase in thickness. At this stage it is un- 
branched, and very little hairy. The only peculiarity, which may 
deserve mention, consists in the presence of a broad pith. Beside 
that the hadromatic rays are very short and separated by broad 
arches of leptome; otherwise the structure is very simple. The 
cortex is homogeneous, there being no exodermis and no stereids, 
but about ten strata of thinwalled parenchyma, very compact, and 
with no deposits of starch. Endodermis is, also thinwalled with the 
Casparyan spots plainly visible, and the pericambium is continuous 
represented by a single layer; the stele is tetrarch. Later on when 
the seedling is at the stage shown in the accompanying figure 1, the 
root has commenced to branch, and has increased considérably i in 
length. At this stage the internal structure is changed, and to such 
an extent that the pith and the primordial vessels are the only tissues 
left intact.  Epidermis is now partly thrown off, nearly the whole 
cortex is collapsed so as to form wide cavities, and the thickened 
endodermis shows here and there radial divisions. Inside endoder- 
mis we notice a broad secondary cortex, developed from the peri- 
cambium surrounding a solid stele of collateral mestome-strands 
and a central pith, at the periphery of which the four primordial 
hadrome-rays are still to be recognized. Starch was observed in 
the narrow (one row) medullary rays, but no crystals of calcium 
oxalate. In regard to the lateral roots, borne upon the primary, 
the structure agrees with that of the mother-root before the 
secondary formations set in; these are, however, also capable of in- 
creasing in thickness, but much later than the primary. 
A still more modified structure occurs in the thick, woody roots 
of the mature tree. In these all the primary tissues from epidermis 
to endodermis incl. are lost, but replaced by a heavy coating of 
homogeneous, thickwalled cork of pericambial origin, which en- 
closes a broad secondary cortex with aggregated crystals of calcium 
oxalate, deposits of starch, and interspersed with groups of thick- 
walled, porous sclereids. The stele is very broad, with numerous 
wide tracheids, thickwalled parenchyma and libriform; the medul- 
lary rays are thinwalled, and consist mostly of a single or two rows 
of radially stretched cells, containing starch. 
While thus the root of our Nyssa illustrates the general 
Structure of the dicotyledonous type so far as concerns the primary 
and secondary stages, the presence of crystals and sclereids in the 
Secondary cortex is of some interest. 
