ground. The stem may be recognized through the presence of 

 leaves or scales. Quack grass, Germander, Northern nut grass, 

 and Morning glory spread by stems. The Quack grass stems, 

 called roots commonly are near the surface of the soil, some- 

 times over three feet long, and every severed part gives rise 

 to a new plant, (b) These plants spread by roots, sometimes 

 they are flehsy and in other cases they are thin and slender. 

 Dock, Horseradish, Horse nettle, Sheep sorrel and Dandelion. The 

 Milkweed spreads horizontally in the soil and may attain a length 

 of 14 feet. The roots of the Horse nettle on the other hand 

 spread deeply in the soil, sometimes to a depth of three and one- 

 half feet. These roots, when severed give rise to new plants, 

 buds forming on these roots, (c) The third type propagates 

 partly by root and partly by stem. The upper part of the 

 Canada thistle is stem, bearing minute scales (leaves), the lower 



root which develops buds. 



Seed Propagation. The vast majority of weeds produce seeds. 

 The only weed in the state which has never been known to pro- 

 duce seed is the Horse Radish. It flowers frequently but seeds 

 are never produced. The Canada thistle blossoms freely but it 

 does not seed abundantly. At least this is true for Iowa. It 

 relies chiefly, therefore, on vegetative reproduction. The quack 

 grass spreads as freely by seeds as by its underground stems. 

 Some weeds produce an enormous number of seeds, from a 

 few thouand to over a hundred thousand on a single plant. A 

 single seed of Squirrel tail grass germinates, from this seed a 

 large number of stems arise, each with a spike that contains 50 

 or 60 seeds, so that the progeny soon becomes greatly multi- 

 plied. 



Dr. Beal estimates that a large purslane plant produces 1,250,- 

 000 seeds, a patch of daisy fleabane 3,000 to the square inch. 

 We found the following number of seeds per plant, horseweed 

 324,000; pigweed, 115,600; Jimson weed, 89,100. Dr. Halsted 

 found seeds in some weeds as follows: Speedwell, 186,292; 

 Shepherd's purse, 17,600; Pepper grass, 12,225; Charlock, 9,900. 

 Hitchcock and Clothier record the weeds seeds as follows : Yellow 

 foxtail, 113,600; stink grass, 180,000; cocklebur, 9,700. 



DISSEMINATION OR SCATTERING OF PLANTS. 



The scattering of plants is called dissemination and this is 

 accomplished in the following ways: (a) wind; (b) water; (c) 

 animals; (d) explosive properties; (e) seeds burying them- 

 selves; (f) man as an agent. 



Wind. The wind is an important agent in a large number 

 of weeds. The dandelion may serve as an illustration. The 

 "seed" is cylindrical with a long beak, coming from the beak 



