CHANGES ACCOMPANYING BREAKING OF REST PERIOD 5 



the rest period of seeds in herbaceous and woody species is very 

 similar to that of the parent plan . 



The cause of the rest period is not definitely known. It has been 

 attributed to both inner causes and environmental conditions. How- 

 ever, the experimental evidence presented in this bulletin strongly 

 indicates that all the phenomena connected with the entire resting 

 phase, are closely associated with the work of enzymes. The begin- 

 ning of the rest, particularly in woody plants, appears to be wholly 

 due to inner causes, but before the complete state of rest is reached, 

 outer conditions may help to hasten the approach of the period of 

 dormancy. In like manner the ending of the rest may take place 

 from inner causes but may be either hastened or delayed by the 

 environmental conditions under which the plant is growing. For 

 the most part, tho, it may be said that the rest sets in and later passes 

 away, independent of outward conditions. 



Why the length of the rest period varies so greatly among the 

 different species is not known. Apparently tho, this is due to hered- 

 itary causes as all the manifestations of the rest, so far as we are 

 informed, are fairly constant for each species. This is particularly 

 true of woody forms. Even with a constant supply of warmth and 

 moisture many woody plants of the temperate zone pass into a state 

 of rest and shed their leaves. There are no data showing that inves- 

 tigators have tried to prevent the rest of such plants from setting 

 in. Herbaceous forms behave differently. Klebs 1 by certain cul- 

 tural methods, actually prevented the rest period, or at least the 

 winter rest, from beginning with certain herbaceous plants, thus 

 causing them to make an uninterrupted growth thruout the year. 



For the purposes of the present discussion, the rest period may 

 be defined as a phase or stage in which plants are, for the most part, 

 incapable of responding to favorable growing conditions. 



It has been thoroly proven that by means of various treatments, 

 the rest period of plants, as well as seeds, can be broken and the 

 plants and seeds revived, thus causing them to begin growing within 

 a few days or a few weeks. Various rest breaking agents, such as 

 ether, frost and desiccation have been employed. Many other ma- 

 terials have been used with success by various investigators. 



Johannsen 1 succeeded in breaking the rest period of many plants 

 by exposing them to ether or chloroform vapors. Molisch 2 origin- 



1. Klebs, G., Willkiirliche Entwickelungsanderungen bei Pflanzen. pp. 

 129-138, 1903. 



1. Johannsen, W., Das Aetherverfahren beim Friihtereiben mit Besonderer 

 Berucksichtigung der Fliedertrieberei, 1906. 



2. Molisch, H. f Forcing Plants by Warm Baths. Sci. Amer. Sup. 66 

 (1908) Exp. Sta. Rec. 20, p. 640. 



, Radium as a Means of Forcing Plants. Exp. Sta. Rec. 27, 



p. 437. 



