156 MINNESOTA liOTANICAL STUDIES. 



In many plants only certain parts were affected. In general 

 flowers, flower-bnds and fruit proved less hardy than the vege- 

 tative parts of the same plants. Also, parts in active growth and 

 those well filled with water were less hardy than the same organs 

 in a less active condition. Thus, leaf-buds which had scarcely 

 started were more hardy than those which had progressed fur- 

 ther, half-grown leaves were very tender, while the fully expanded 

 and ripened leaves were more hardy again. In the same manner 

 opening flower-buds and the expanded flowers were more tender 

 than either small buds or ripening fruit. Several peculiar cases 

 of selective killing were noted. Thus, in several plants the pistil 

 was killed w-ithin an otherwise uninjured flow^er-bud. This hap- 

 pened in nearly all the unopened buds of the apple. Often the 

 flowers afterwards expanded as if uninjured. In Sangninaria the 

 ovules were killed within the developing fruit, while the pericarp 

 was uninjured and continued to grow for several weeks. 



Relative Injury to Different Types of Vegetation. (1). Her- 

 baceous Vegetation. — Native perennial herbaceous vegetation suf- 

 fered surprisingly little damage. Less than 50 per cent of these 

 plants were hurt at all, and in these cases injury was mainly me- 

 chanical, or confined to flowers, the edges of unfolding leaves, ripen- 

 ing fruit or similar tender parts. By the middle of May native her- 

 baceous vegetation had an entirely normal aspect. That it had re- 

 ceived no serious check was shown by the fact that until late sum- 

 mer it remained several weeks ahead of the usual seasonal develop- 

 ment. This immunity to injury was not due to any great extent to 

 the more protected position of the herbs but to an actual hardi- 

 ness far in excess of that shown by woody plants. Exotic garden 

 plants did not possess it to any great extent. It was more notable 

 among the plants which form the vegetation of the exposed prai- 

 ries than in the case of the comparatively sheltered herbaceous 

 undergrowth of the forest. In fact, nearly all of the native her- 

 baceous plants which were injured were among those growing in 

 the latter situation. As the actively growing parts of herbaceous 

 plants are not per se any more capable of withstanding hard 



♦About 5 per cent of trees and shrubs were still in a dormant condition, 

 and were uninjured. 



