REST PERIOD OF PLANTS 191 



Dormancy in bulbs is desirable while they are in storage and 

 until they are planted. Near the end of their dormant period 

 a very short exposure to a warm temperature may break it. 

 In the earlier period of their dormancy alternate cold and 

 warm is effective. Most dormant perennial plants and seeds 

 will also have this resting period shortened in either of these 

 two ways. Treatment with any one of a number of gases is 

 effective with most plants and seeds. Ether, ethylene dichlo- 

 ride, ethylene chlorohydrin, carbon bisulphide, and others 

 have been used. 



Dormancy has been studied more in seeds than in other 

 parts of plants, and in addition to treatments described 

 above, most seeds have their dormancy shortened by a natu- 

 ral warm-cold treatment called "stratification." The seeds 

 are mixed with peat, sand, or sawdust, kept moist, and put 

 in the soil where the temperature will fluctuate between 

 freezing and a few degrees above. This method is commonly 

 followed also where incubators can be used to control the 

 temperature at P C. to 5° C. Rose seeds may be planted in 

 outdoor flats, where germination should be allowed to go on 

 for at least twenty months with frequent examination to 

 remove the seedlings. Some species of rose, as multi-flora, 

 germinate within four months in favorable conditions, but 

 most species and hybrids require careful stratification and 

 the longer period. Some seeds, such as bluegrass, and let- 

 tuce, have their germination hastened with light, and others, 

 such as Datura, in the absence of light. 



The rest or dormant period of plants is used constantly 

 in gardening. We do the main pruning and transplanting of 

 perennial plants during the dormant period. Plants store 

 food and grow large root and shoot systems during the 

 active period, and the food reserve that has been stored can 

 be used for growing the new absorbing root system, and send- 

 ing out a new set of leaves. The least damage is done in 

 transplanting at the dormant period because of the reserve 



