10 DURATION OF LIFE [CH. 



soils. In old lawns, pastures, &c., the roots of Poa annua 

 and others may have nodules on them due to the presence 

 of certain small Nematode worms, Heterodera. 



Grasses are annual, biennial, or perennial, and it is 

 often of importance to know which. The point may usually 

 be determined by examining the shoots. If all the shoots 

 have flowering stems in them, and are evidently of the 

 current year, the grass is an annual; but if any shoots 

 have leaves only, it is either biennial or perennial : to 

 determine which is not always easy, but in perennial 

 grasses there will generally be evident remains of older 

 leaf-bases and shoots, and if there are distinct under- 

 ground stolons or creeping rhizomes as well the point 

 may be considered decided, and the grass is perennial, as 

 is the case with most of our important species. If all the 

 shoots are barren, the grass is a biennial in its first year 

 of growth : if all have flowering stems in them, but show 

 traces of old leaf-bases of the previous year, then the grass 

 is a biennial in its second year. The proof of biennial 

 character is not always easy, however, and a few grasses 

 may be either annual or biennial, or biennial or perennial, 

 according to conditions — e.g. species of Hordeum, Bromiis, 

 &c. In the following lists I have given the duration of 

 the principal grasses, where the character is especially 

 important. 



Annuals. 



Phlewn areiiarmm. Loliiim temrdentum. 



Aira prcecox. Festuca Mywrus. 



A. caryophyllea. Briza minor. 



Hordeum murimim. Poa rigida. 



H. maritimum. P. annua. 



