i64 



Bulletin No. 205 



[March, 



THE STRUCTURE OF GRASSES 



Grasses belong to the family Poaceae, or Gramineae, which 

 includes between three and four hundred genera. Sixty-three genera, 

 exclusive of the cultivated grasses called grains, are found in Illinois. 

 These genera include the two hundred and four species known to 

 occur in the state. 



There are few plants likely to be mistaken for grasses. The sedges 

 resemble them most but are easily distinguished by their three-ranked 

 leaves and solid stems (Fig. 2). Grasses have two-ranked leaves and 

 usually hollow stems (except in Maydeae and Andropogoneae, of 

 which Tripsacum and Andropogon are typical'genera) (Fig. 1). 

 According to their length of life, grasses are classed as follows: 

 An7iual Grasses. — Many species of grasses live but one year. The 

 seeds of the preceding year germinate in spring or early summer and 

 ripen seed in the summer and fall. Common crab grass, SyntJierisma 

 sanguinalis, old witch grass, Panicum capillare, and Indian corn, Zea 

 mays, are well known examples of annual grasses. 



Figs. 1-4. — 1, Portion of grass culm showing 2-rankecl leaves; 2, Portion of 

 sedge culm showing 3-ranked leaves; 3, Portion of grass plant showing fibrous 

 roots; 4, Portion of grass plant showing rootstocks 



Winter Annuals. — In our latitude the seeds of certain annual 

 grasses may germinate in the fall and live over winter in small tufts, 

 sending up their flower stalks in early spring. These are known as 

 winter annuals. Low spear grass, Poa annua, little barley, Hordeuni 

 pusillum, and the varieties of winter wheat are common examples of 

 winter annuals. 



Perennial Grasses. — These grasses are propagated both by seeds 

 and by rootstocks. There are two types of perennial grasses in Illi- 

 nois. In one (Fig. 3), the stem dies back to the base each winter and 



