CHANGES ACCOMPANYING BREAKING OF REST PERIOD 21 



outgrew the etherized ones even tho the latter opened a day or two 

 before. These forcing results with apple twigs are very similar to 

 those given by Johannsen 1 for bulbs. 



The results of these respiration experiments are discussed on 

 page 45. 



EXPERIMENTS ON ENZYME ACTIVITY 



It is known that enzymes will become inactive if the products 

 of their work are not utilized in some way or other. 2 As Klebs 3 

 points out, the leaves of many plants continue to elaborate food in 

 autumn for some time after length growth has ceased. As a result, 

 the assimilated food accumulates so that the work of the ferments 

 is greatly hindered until they finally become entirely inactive. As 

 previously stated, Klebs believed that every rest period can be 

 broken if it is found possible to arouse enzymic activity. Do agents 

 which break the rest period have an effect on the enzyme activity 

 of the twigs? The object of the following experiments was to deter- 

 mine just what effect some of the principal rest period breaking 

 agents have on these ferments. 



Experimental Material, Methods, etc. For the most part, 

 one-year-old apple twigs were used in these experiments. In a few 

 cases older wood was made use of. The material was taken from 

 vigorous Jonathan, Ben Hur, Ben Davis, Payne's Keeper, Red June 

 and Nixonite apple trees, growing in the station orchard at Colum- 

 bia, Missouri. The enzyme activity of one-year twigs of Quercus 

 coccinea, Fraxinus Ornus, Forsythia suspensa, and Prunus Persica 

 was also determined. 



Method of Collecting. The method of collecting the one-year 

 twigs and then dividing them into similar lots was the same as here- 

 tofore described. To obtain comparable samples of old wood, alter- 

 nating sections of the same branch were used for treated and for 

 untreated material, respectively. When the enzyme activity of 

 buds alone was to be tested, large branches containing an abundance 

 of spurs were collected. These were then cut into smaller parts. 

 Similar parts growing adjacent to each other were divided into lots 

 to be treated and lots which were to remain untreated. 



1. Johannsen, W. Das Aetherverfahren beim Friihtreiben, etc. Zweite 

 Ann. Jena 1906. 



2. Pfeffer, W. Pflanzenphysiologie Bd. II. 1904. Especially the chapter 

 on Periodicity. 



3. Klebs, G. Ueber die Rhythmik in der Entwickelung der Pflanzen. 

 Bot. Cantbl. 119 (1912) p. 426. 



