STEMS 



mously. Thus in some of the lower forms an indi- 

 vidual may be grown from a spore, attain maturity, 

 give rise to new individuals, and die in a few hours 

 or even in a few minutes. The spores of these same 

 species may be capable of living many years in a 

 resting condition, however. Among the seed plants 

 the cycle of life varies from sixty or seventy days in 

 some of the herbs to three thousand years in certain 

 kinds of trees. It is estimated that some trees can 

 live to twice this age, though the lack of records 

 does not allow this to be verified. The estimation of 

 the age of a tree by counting the annual rings is 

 subject to error, since the number of these rings may 

 be nearly twice the age of the tree in years. All 

 seed plants may be roughly classed as annuals, bien- 

 nials, and perennials. 



154. Annuals. Annuals are those which live 

 but one season. The seeds germinate, and a system 

 of roots, a stem, and branches are formed, and seeds 

 are matured in a period which varies from two to 

 four months. Species of this character may gener- 

 ally be distinguished by the character of the stem 

 and root system. Annuals live through the winter 

 in the form of seeds only. Examine twenty species 



