62 A LABORATORY MANUAL OF BOTANY 
greenhouses will afford interesting and instructive work. 
An excellent series of lessons can be planned in studying the 
seasonal changes in societies. The substitution of one soci- 
ety by another may be well studied in any locality where 
there are ponds which become dry for quite a period each 
year. 
In planning work on plant societies, as well as in other 
work, each teacher must adapt his outline to conditions pe- 
culiarly favorable for work in his locality. 
