108 1.8.C. Proceedings of the Ninth [N.S., XVIII, 
fertile field confronting us just now; and the work does not 
require either long intensive training, or excessive outlay on 
material equipment. The most accessible problems fall into 
three groups : 
1. Descriptive studies. 
. Response of the vegetation to the periodic climate. 
3. ect of man on the vegetation. 
Descriptive studies will work out the great formations of 
the natural vegetation, and relate them to the climatic factors. 
This will include a study of the successions leading up to the 
climax vegetations. As these studies become more exact, they 
will increasingly require the use of instruments for determining 
the details of the climatic factors and their influence in deter- 
mining distinct types of vegetation. We have the meteorolo- 
gical records available, but they give little clue to local devia- 
tions of moisture, humidity, insolation, temperature, and ex: 
posure to wind, that are so important in causing local differ- 
ences in vegetation. 
Considerable effort has been made in the West toward 
developing exact statistical methods of describing vegetation. 
Perhaps the work of RaunkraER! is best known. “ 
doubtedly such efforts are still unsatisfactory, but they make 
it possible to compare directly the vegetations of widely sep- 
arated areas, and also to distinguish slight differences in local 
areas. It would be a most valuable contribution to have our 
ee types of vegetation studies by such statistical me- 
thods. 
e response of plants to our periodic climate offers 
an equally fruitful field for detailed studies. There is little bo- 
dual plant is one that offers many points of approach, an 
that can be undertaken almost anywhere by anyone sufficient- 
ly interested. 
It is commonly considered that leaf fall is caused by 4P- 
proaching excess of transpiration over water intake. In tem 
perate regions this is brought about by increasing cold slowing 

ce 
' Raunkiazr,C. Recherches statisques sur les formations végé- 
tales. Kg. Danske Vidensk. Selsk., Biol. Meddelelser 13: 1-80. 1918. 
