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 Howering 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, Bromus, 
&c. In the following lists I have given the duration of 
the principal grasses, where the character is especially 
important. 
ANNUALS. 
Phleum arenarium. Lolium temulentum. 
Aira precon. Festuca Myurus. 
A. caryophyllea. Briza minor. 
Hordeum murinum. Poa rigida. 
H. maritimum. P. annua. 
