THE AMERICAN BOTANIST. 77 



Poison Ivy in England. — According to the Gardening 

 World our common poison ivy (Rhus toxicodendron) is 

 ■often planted in private gardens in Great Britain. 



Willows Used in Pharmacy. — According to the Gar- 

 dening World it is only certain species of willow whose 

 bark yields the salicin of the shops. Experiments have 

 shown that in England the best yield of this product was 

 from Salix triandra,S.. purpurea^ S. rubra andS. decipiens. 



A Seed Problem. — Happening to examine some seed- 

 pods of Baptisia lencophaea recently, our attention was 

 drawn to the fact that the individual seeds are covered 

 •over witJi tiny dots of a resinous substance so sticky that 

 the seeds stick to each other and to the pod in which thej'^ 

 are enclosed. Now the question is, Why this resin ? Are 

 w^e to assume that it is a mere by-product, or of some ser- 

 vice to the seed ? 



Frost and Falling Leaves.— Man\^ plant students 

 are likely to think that the frost is responsible both for 

 the color of autumn leaves and for their falling from the 

 tree. This, however, is a mistake. Frost may make some 

 flight changes in the color of the leaves, but the effect of 

 frost on tender herbage is to wilt rather than to color it. 

 Long before there is a hint of frost in the air the trees and 

 shrubs have begun to move from the leaf into the trunk 

 .such substances as it can use and at the same time begins 

 the formation of a cleavage plane which when complete 

 Avill sever the leaf stem from the twig. It thus happens 

 that trees often cast their leaves before there has been a 

 frost while even after several hard frosts other trees still 

 retain a part of their leaves. There is a phenomenon con- 

 nected with this, however, which seems as yet unexplained 

 and that is the way in which certain trees suddenh'' cast 

 all their leaves. This year, in the region south of Lake 

 Michigan, the night of October 23rd was the crisis. Up 

 to this time many had stood fresh and green but on the 

 morning of the 24th, when there was a heavy frost, every 

 leaf was stripped from them. The Ailanthus became an 

 utter wreck in a single night. The day before, its long 



