106 



PLANT GROWTH 



tive methods. Most garden weeds are annual but the weeds 

 in the lawn are of all three classes. 



Weed seeds have well-fixed rest periods which have 



Fig. 19. Vegetative propagation of weeds by modified stems. A, Ranunculus 

 bulbosus, corm. B, Allium vineale, bulb. C, Helianthus tuberosus, tuber. D, Agro- 

 pyron repens, rhizome. E, Convolvulus sepium, rhizome. F, Hieraciutn pratense, stolon. 

 G, Achillea Millefolium, rhizome. H, Veronica serpyllifolia, creeping stem. Reduced to 

 about 1/3 natural size. (From Muenscher's Weeds. By permission of The Macmillan 

 Co., publishers, 1936.) 



enabled them to persist in various habitats. Many of them 

 will remain in the soil for several years, after which they will 

 germinate. Table II in the book on "Weeds" by Muenscher 



