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IOWA ACADEMY OF SCIENCE 
surrounds the cortical parenchyma, also thick walled in which are stored large, 
eccentric starch grains which resemble those found in the potato tuber. The 
fibroyascular bundles are of the open collateral type, with sieve elements next 
to the cortex, the xylem next to the pith and separated from the phloem, by 
the cambium. The medullary rays extend from the cortex to the pith and 
contain a few starch grains. The parenchyma cells of xylem are thick walled. 
Root. The tortuous roots vary a great deal. In younger specimens they are 
somewhat slender, becoming thick and hard with ages, lightly brown in color 
with strong odor. They extend vertically into the soil from one to four feet 
or even five feet. Numerous adventitious buds are produced along the course. 
A microscopical study shows that the organs which produce the buds are 
roots; these are the usual radial bundles, but the medullary rays secondary and 
primary are small and lie between the xylem elements. In the secondary 
structure a few layers of cork cells are developed and underneath a large num- 
ber of parenchyma cells with walls somewhat thicker than those of the cork 
cells. These are abundantly filled with large starch grains and a considerable 
quantity of protein matter. The bulk of the root consists of the cortex. The 
xylem is separated from the cortex by a well defined area consisting of the 
endodermis a few layers of very thin walled cells. The medullary rays are 
harrow and extend into the xylem area between the bundles. These cells also 
contain starch grains. The xylem elements consist of scalariform and pitted 
ducts. 
Asclepias syriaca L. Milkweed. 
Roots. The roots of Milkweed have been traced in the soil for fourteen 
feet. They are generally horizontal though occasionally vertical. A single 
root removed from the soil and placed in a moist place at once produced adven- 
titious buds along its surface. At very short intervals several dozen of these 
buds' could be made out with the naked eye; many more could be made out 
when sectioned. 
The roots are whitish and much thickened. Microscopically the roots show 
that the bundles are of the radial type. The structure in an older root shows 
thin walled epidermal cells nearly isodiametric although in some cases longer 
than wide. Underneath the epidermis there are two or three layers of thin 
hypodermal cells. The cortex is differentiated into two parts, the outer por- 
tion of large irregular thin walled cells and small intercellular spaces and the 
inner cortical region of cells which become smaller toward the endodermis. 
The cells of the cortex contain a large number of small starch grains and 
compound calcium oxalate crystals. In secondary growth the xylem consists 
of bundles of scalariform ducts varying in number from one to five, which are 
scattered throughout the parenchymatous tissue of the vascular region. Starch 
grains and calcium oxalate crystals are also found in this parenchymatous 
tissue. 
Stem. The difference in the origin of lateral roots and that of adventi- 
tious buds on the root was studied somewhat at detail in the Milkweed. 
Lateral roots originate endogenously within the vascular bundles and with 
a well defined protoxylem push through the cortex. On the other hand stems 
originate possibly from a single cortical cell just underneath the epidermis. 
This cell becomes actively meristematic and soon involves other cells which 
differentiate definitely into plerome and periblem. The epidermis lying just 
