INTRODUCTORY 5 



end of the growing season, the parts of the plant which still 

 remain to carry on growth in subsequent years being under- 

 ground : the stinging nettle, hop, and potato are representa- 

 tives of this class. In woody perennials, of which all trees 

 and shrubs are examples, the stems above ground are hard 

 and woody. 



This method of dividing plants according to their length of 

 life, although useful, is by no means a strict one, as the duration 

 is dependent to some extent upon season, time of sowing, and 

 the treatment which they receive. Wheat, for example, if sown in 

 early spring behaves as an annual, but if sown in late summer or 

 autumn does not perfect its seed and die until the following 

 year. If kept continually cut or cropped down by animals it 

 may even remain two years or more without dying, especially when 

 thinly sown on good soils and allowed plenty of room for branch- 

 ing. Annual mignonette of gardens is often made to last several 

 years in pots by pinching off the flowering stems as soon as they 

 begin to form. 



Turnips and other plants, usually biennials in ordinary farm 

 practice, are invariably annuals if sown early in the year, say in 

 February. 



Climate and soil also influence the duration of plants, annuals 

 in some districts becoming biennial or even perennial in others. 



Ex. 1. — Sow short rows ol the cereals and ' roots ' — mangels, turnips, 

 swedes and carrots — on the first day of each month during a whole year, and 

 make careful observations and notes on their subsequent growth up to the time 

 of seed production. Interesting and useful results are obtained. 



5. As the duration of flowering plants is subject to such varia- 

 tion and their classification into annuals, biennials, and peren- 

 nials, consequently somewhat arbitrary, they are sometimes 

 placed in groups according to the number of times they are able 

 to produce seeds. 



Those which yield only one crop and then die are termed 



