IOWA ACADEMY OP SCIENCE 
33 
at which these huds occur varies from a few inches to more than two feet from 
the surface of the ground. It is not unusual for others among our common 
thistles to produce adventitious huds. This is indicated hy Hitchcock and 
Clothier^- for Cirsium undulatum. It is also true for Girsium canescens^^ which 
spreads much like Canada Thistle. Dr. Bessey writes us that he observed 
this many years ago for this species. 
The secondary structure is comparatively simple. The epidermis is per- 
sistent. The cortial parenchyma consists of twenty or more layers of thin- 
walled, somewhat irregular cells, and small intercellul'ar spaces. These paren- 
chyma cells are filled with small starch grains. The cells of the endodermis 
do not differ materially from the cells of the cortex. Projecting into the vas- 
cular region and lying between the phloem and xylem plates, are other broad, 
primary, medullary rays much wider in the region of the sheath, gradually 
tapering to a point, toward the center. The phloem elements occur in arched 
area between the medullary rays. The cambial elements lie between the xylem 
and arched phloem. The elements of the xylem consist of scalariform ducts and 
parenchyma cells which are thin walled. 
Stem. In numerous specimens examined by us the shoots coming from the 
roots had small scales and buds along the sides; these for the most part do 
not develop but can do so when the strong terminal bud is cut off or injured. 
The microscopic structure consists of an epidermis of a single layer of cells, 
slightly longer than wide with the outer wall thicker than the lateral walls 
and carrying a brownish pigment. This is followed by the cortex consisting 
of many layers of thin walled irregular cells, in which starch and other reserve 
food products occur. The intercellular spaces are small. The fibrovascular 
bundles are arranged in a circle and are of the collateral type. The scleren- 
chyma elements are arranged across the outer and inner portions of the bundle. 
The phloem is situated between the sclerenchyma and the intrafascicular cam- 
bium. The tracheary elements vary with the size of the bundle. These ele- 
ments consist of spiral, scalariform, and ringed ducts. 
'Conclusion. The most important method of propagation in the Canada 
Thistle is by means of the large roots by which the plant spreads through the 
ground. Such stems as do .not occur in the ground come from the adventitious 
buds on the roots. The seminal roots descend into the soil and later form 
these adventitious buds. Under some conditions, especially when the plant is 
injured or when a new shoot is produced in the spring, adventitious buds may 
be found on the stem. 
Solanum carolinense L. Horse Nettle. 
The roots and stems of some species of the Solanacese have been studied by 
Gerard^^, also by Costantin®^. 
Stem. The twisted woody stem with its numerous lateral roots resembles 
the root in a very striking manner; in fact it is difficult to distinguish root 
from underground stem except by microscopical examination. During the 
winter it dies back near to its origin in the root. The thick walled epidermis 
32L.c:13. 
^^Con. Bot. Dept. la. St. Coll. Agr. and Mech. Arts. 16. 
3^1.c. 375, pi. 18 f. 53-61 
st^l.c. 132. 
3 
