13() 



MASS. EXPERIMENT STATION BULLETIN 276 



00 *C 'H 





CO o 



J3 (M j; N 



+ .5 + = 



^" b ci o c 



CV rt ^. C ^ 



o o 



o -* 



CO Tt 



W CC » M 



t- o 



= 3 S 3 o 



— :s -5 ^ c 



3 - 3 3 O 



VI m ^ m "^ 



►^ ►:; 



iz; ?^ 



'O o « x> ^ 



