Chapter Twenty-Five 

 REST PERIOD OF PLANTS 



Most plants of the temperate zones have developed the 

 characteristic of growing only during the summer. Annuals 

 grow, bear flowers, seeds, reach old age, and die during the 

 summer. The embryo plant of the seed is the only part or 

 stage to have a rest period. At the end of the growing season 

 biennials and perennials go into a dormant or rest period for 

 varying lengths of time, part of which is usually during the 

 winter. The physiology of these adaptations to climate are 

 not understood. The rest period is that time during which 

 a plant or any part of a plant remains dormant or inactive 

 even though it is given all the external conditions necessary 

 for growth, and should be distinguished from the inactive 

 period of stored seeds, due to unfavorable conditions for 

 germination. Most plants, bulbs, tubers, seeds, etc., can be 

 kept in an inactive condition after the rest period is past, 

 by subjecting them to a low temperature and keeping them 

 with a low moisture content. Either a low temperature or 

 a low moisture is often suflficient but both are better. 



Dormant and inactive plants carry on all the activities 

 necessary for life, but at a very low rate. Several thousand 

 bushels of wheat may be kept in storage for months with no 

 thought of its oxygen supply, but the small loss in weight 

 indicates very slow respiration. Dormant seeds usually have 

 more stored food and less water but the water is held more 

 securely in the colloidal mass. The cells are mature, growth 

 has ceased, and the rate of respiration is very low. These 

 conditions enable a plant or seed to withstand extremes of 

 temperature which would be impossible with actively grow- 

 ing parts. This characteristic is most striking among wild 



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