158 MINNESOTA BOTANICAL STUDIES. 



in 1910 appear to be of less frequent occurrence in the parts of 

 the country from which these plants have migrated. This is the 

 probable explanation also of the comparative tenderness of the 

 herbaceous undergrowth of the forest — plants which have un- 

 doubtedly migrated along with the forest trees. 



Recuperation of the Frozen Plants. — Recuperation from the 

 effects of the frosts was often a slow process and much of the 

 woody vegetation had an abnormal appearance all summer. 



In cases where the injury was slight growth was but little 

 checked and proceeded normally. When there was extensive de- 

 foliation any leaves which escaped often grew to unusually large 

 size, and new growth developed in one of several ways. (1). As 

 would be expected many latent buds on the woody twigs and 

 branches sprang into activity. This was more or less true in 

 all cases of severe injury and was the only possible method of 

 recuperation when all of the new growth had been killed. In 

 some cases these buds started to grow on twigs which themselves 

 had been so severely injured that they later proved unable to sup- 

 port the new growth. This then withered and other latent buds on 

 still older twigs were brought into growth.* (2). When the 

 young twigs were partially but not entirely killed, shoots fre- 

 quently appeared in the leaf axils of the lower nodes of the cur- 

 rent season's growth. In some cases these shoots appeared di- 

 rectly without the production of any scaly buds. In other cases 

 buds with a few scales formed and quickly started into growth. 

 As a result of this the season's growth consisted of a main axis 

 with numerous lateral twigs giving the trees a somewhat fasciated 

 appearance. (3). When the injury was confined to the leaves 

 the terminal bud often continued to develop until a sufficient num- 

 ber of new, leaf-bearing nodes were formed. These long switch- 

 like branches were often considerably longer than the normal 

 growth for one season. Some trees employed one of these methods, 

 some another and some used any one of the three, according to 

 the extent of the injury affecting the particular branch. In a few 

 cases recuperation was very slow — it was after midsummer before 



*Many hackberry and ash trees and some oaks showed this effect. It was 

 probably due to the killing of the phloem and cambium of the old twigs. 



