SEEDS AND SEEDING 87 



sorghums and cowpeas, which like maize require a con- 

 tinuous, rather high temperature for their best develop- 

 ment. They are all plants of tropical origin carried by 

 agriculture into temperate regions. All are characterized 

 by rather rapid and uniform growth from germination 

 to maturity. At their northern limits they succeed best 

 if planting is delayed until the latest time which safely 

 permits of their maturing, as their growth is seriously 

 checked by cool weather. Where the season is longer 

 plantings may be timed according to weather and soil 

 conditions ; or better, late varieties which can utilize 

 the longer season may be grown. A few summer annuals 

 like the soybean will withstand cool weather, even light 

 frosts, both in spring and fall, but most of them are in- 

 tolerant of cold. 



Winter annuals include wheat, rye, oats, barley, Canada 

 peas, common vetch, crimson clover and others. Natu- 

 rally, they are plants which germinate in the fall and 

 mature in spring or summer in regions of mild, often 

 frostless, winters. They differ from summer annuals in 

 being intolerant of high temperatures during growth, 

 and in undergoing more or less dormancy during winter. 

 Where the winters are too severe they must be planted in 

 spring, but in such cases often suffer from summer heat, 

 as commonly occurs with Canada peas and common 

 vetch. Where both fall and spring sowings are possible, 

 as wheat in some regions, the former usually produce 

 better crops, owing partly to better root development, 

 and partly to the longer growing season in spring which 

 fall planting insures. To a slight degree winter annuals 

 show a dual period of development like biennials. 



Biennial plants like the carrot, beet and rutabagas 

 are especially instructive, in that their development 



