4 
AMERICAN MIDLAND NATURALIST. 133 
somewhat more advanced stage (Fig. 9.) we notice in this paren- 
chyma a beginning development of leptome (L. in fig. 9.) beside 
tangential divisions, indicating the origin of an interfascicular cam- 
ium in direct connection with the primary intrafascicular. It is 
from the interfascicular cambium that the secondary leptome and 
hadrome become developed, rapidly increasing in thickness so as to 
equal the primary. In regard to the other tissties of the hypocotyl 
we might mention that near the base the cuticle is thin and smooth; 
covering a small-celled, thinwalled epidermis destitute of hairs. 
Furthermore that the cortex is homogenous, thinwalled, frequently 
collapsed, and that the hypodermal stratum shows a formation of 
cork. There is a distinct endodermis, thinwalled, but readily 
noticeable by the Casparyan spots, and inside this sheath is a 
thinwalled pericycle, which in the apical portion of the hypocotyl 
omes stereomatic, but as already indicated only outside the pri- 
mary leptome. Near the cotyledons the epidermis becomes thick- 
walled with the outer cell-wall extended into minute longitudinal 
crests, and the cortex is here solid, not collapsed. No crystals of 
calcium oxalate were observed in any parts of the hypocotyl. 
somewhat modified structure occurs in the first internode of the 
same seedling (Fig. 1.) In this the cortical parenchyma consists of 
collenchyma near epidermis, while the internal strata are thinwailed 
and contain large, single crystals of calcium—oxalate, besides some 
aggregates of the same substance. There isno endodermis, but a peri- 
cycle of isolated strands of typical stereome surrounding the stele. 
The seedling, thus, illustrates the primary structure and certain 
parts of the secondary, not only within the stele, but also near the 
periphery, when the cork has already made its appearance. 
If we now examine branches of the mature tree, we meet with 
a much firmer structure; the cork représents here numerous and 
very thickwalled strata, covering a cortex which is collenchymatic 
throughout, and rich in chlorophyll; then follows the pericycle of 
thickwalled stereome intermixed with large, porous sclereids, form- 
ing a closed sheath — the stele. In this the secondary hadrome 
contains scalariform vessels, porous tracheids with bordered pits, 
and much thickwalled Medeam: the medullary rays are single' with 
the cells stretched radially and filled with starch. Thecentreof the 
stele is occupied by a heterogeneous pith, starch-bearing and active 
in the periphery, but empty in the centre. A corresponding 
Structure recurs in the peduncle, when the fruit is ripe. However, 
