REST PERIOD OF PLANTS 189 



plants, where the seeds may be matured in early summer and 

 lie unprotected in a dormant condition until the following 

 spring or in some cases for a much longer time. The rosette 

 stage, frequently on a fleshy root, developed by a biennial 

 remains dormant over winter and grows a tall shoot with 

 seeds the next summer, as in carrot (Fig. 18). Perennials 

 remain dormant in winter but grow and produce seeds each 

 summer. This characteristic rest period is so deeply fixed in 

 oaks that the seedlings grown in the greenhouse for four 

 years continued to lose their leaves and remained dormant 

 during the winter but their leaves commenced to grow each 

 spring only about two weeks before those of the oak trees 

 outside the greenhouse. 



Dormancy is more deeply fixed in certain species than in 

 others but in all cases it appears to be stronger in the early 

 period and appears to weaken as the period progresses. To- 

 ward the end of the period it is easily broken in most plants. 

 Bulbs, tubers, seeds, and branches of flowering shrubs may 

 be forced in most cases by treating with warmth of 30° to 

 35° C. for twelve to twenty-four hours, if treated near the 

 end of their dormancy, but more drastic treatment would be 

 required at an earlier period. 



The dormant period is not always in the winter; crocus, 

 tulip, spring beauty, and many other bulbous plants begin 

 the dormant period in late spring and begin root growth in 

 the late fall or in mid-winter. The bearded iris has a period 

 just after flowering that approaches a dormant condition. 

 All bulbs and rhizomes may be transplanted most effectively 

 during the dormant period. 



The seeds of many of our cultivated plants have a very 

 short or no dormant period. Grapefruit seeds are often 

 germinated in the fruit. Beans and peas may sprout in the 

 pod if it falls on the ground. The farmer uses care in shock- 

 ing his grain to prevent its getting wet enough to cause it to 

 sprout before it is dry enough to put in storage. Some spe- 



