32 
IOWA ACADEMY OP SCIENCE 
Horse Nettle is abundantly propagated by slender perennial rootstocks, while 
others state that it propagates by roots. With reference to the Canada Thistle, 
Vasey and CrozieP% Goff and Mayne^'^ and Dr. Gray state that the plant has 
creeping rootstocks which spread in every direction. 
Besides one of the present authors^®, many other writers have accepted and 
made similar statements without giving the subject much attention. 
Anatomical Structure. 
Since the general characters will not always enable one to determine the 
nature of the underground organ, a microscopical study was made. In this 
way, we were able to determine definitely the extent of the root and stem. 
The microscopic structure of roots and their origin is sufficiently indicated 
in many special treatises on this subject, especially by such writers as De 
Bary^®, Vesque^^ Marie^®, Jeffrey^®, Costantin^® Gerard^\ WorsdelP^ SargenP®, 
Van Tieghem-^ Strasburger, Noll, Schenck, and Karsten^®, Solreder^ Holm-\ 
Andersson^®, DodeP®, Goldsmith®®, and Van Tieghem®^. 
Girsium arvense (L.) Scop. Canada Thistle. 
Root. The root is usually horizontal or occupies a vertical or oblique posi- 
tion in the soil, frequently strongly contorted; whitish or light brown with 
a strong odor; the small roots occur on the stem without definite order; when 
immersed in water a blackish extractive matter is removed. The thicker roots 
produce numerous adventitious buds along their course. The depth in the soil 
iq.c. :85. 
i3Lc. :109. 
i^Syn. FI. of N. A. i:393. 
^^Pammel. Bull. la. Agr. Exp. S'ta. 70 :324. 
i®Comparative Anatomy of the Vegetative Organs, of the Phanerogams and Ferns. 
English Translation by Bower and Scott. Oxford. 1886. 
i^De’l Anatomie des tissus appliquee a la Classification des plants. Nouv. Arch, la 
Mus. d’ Hist. Nat. II. 5:291. 
i®Recherches sur la structure des Renonculacees. Ann. d. Sci. Nat. Bot. VI. 20: 1-180. 
8 pi. 
^®Coulter and Chamberlain, Morphology of Angiosperms. 311. The Morphology of the 
Central Cylinder in the Angiosperms. Trans. Can. Inst. 40. pi. 7-11. 
-®Costantin. Etude comparee des tiges aeriennes et souterraines des Dicotyledones. 
Ann. Sci. Nat. Bot. VI. 16:1-176. pi. 1-8. 
2iRecherches sur le passage de la Racine a la Tige. Ann. Sci. Nat. Bot. VI. 11:279- 
430. pi. 1-18. 
22A study of the Vascular System in certain orders of the Ranales. Ann. Bot. 22 : 
651-628. pi. S2, S3, 5of. 
2®A Theory of the Origin of Monocotyledons founded on the Structure of their Seed- 
lings. Ann. of Bot. 77:1. 7 pZ. 10 f. 
-^Recherches sur la symetrie de structure des plantes vasculaires. Ann. Sci. Nat. V. 
78:185. 
2®A text-book of Botany. Eng. Trans., Lang. 128, 142, 154. 1908. 
2®Syst. Anat. d. Dicotyledonen, 1899. 
27Am. Jour. Sci. y/:298. (1897); 9:355. (1908). 9:355. (1900) 7:5. 1899. 
28Ueber die Entwickelung der primaren Gefassbundelstrange der Monokotyledonen. 
Bot. Centrbl. 87:586. 
29Der Uebergang des Dicotyledonen Stangels in die Pfahl Wurzel-Pringsheim Jahrb. 
8:149-193. pi 11-18. 
soBeitrage zur Entwickelungsgeschichte in Stengel und in der Hauptwuzel der Dico- 
tyledonen — Dissertation. 1876. 
siTraite de Botanique. 686, 750. 
