Ill 



relating to rainfall, evaporation, and temperature. In a series 

 of experiments conducted during the past summer and described 

 in detail elsewhere^ it was demonstrated that, taking the ratio 

 between the amount of water precipitated in the form of rain 

 and that lost by evaporation as a criterion, there is a distinct 

 correlation between the quantity of water theoretically available 

 for plant use during the growing season and the distribution of 

 forest types. In brief, it was found that while during the period 

 of observation the rate of evaporation throughout the state far 

 exceeded the rate of rainfall, there was an appreciable difference 

 in the ratios between loss and gain in different regions. The 

 estimated ratios were as follows : (a) western highland (interior) 

 — .46; {b) central lowland (interior) — .35, coast — .36; (c) 

 eastern highland (interior) — .31. These regions coincide ap- 

 proximately with {a) the northern hardwood area ; ih) the sprout 

 hardwood area dominated by chestnut ; and (c) the sprout hard- 

 wood area dominated by oaks. Similarly temperature suggests 

 a plausible explanation for the restriction of so many southern 

 species to the immediate proximity of the coast, for while the 

 length of the growing season in the interior averages 148 days, 

 it is found that along the shore 177 days normally intervene 

 between the last killing frost of spring and the first killing frost 

 of autumn. It may be worthy of note also that in passing from 

 east to west along the coast — from the shore of the ocean to the 

 shore of Long Island Sound — there is a gradual diminution in 

 the length of the season from 194 days at New London to 159 

 days at Norwalk. The longer growing season in southeastern 

 Connecticut might be urged as a possible explanation for its 

 peculiar flora, but an objection to such a view is the fact that 

 over half of the plants noted above as confined to this section of 

 the state have been found more than ten miles inland, notably 

 at Voluntown where the growing season averages less than 140 

 days. The climate of northwestern Connecticut, on the whole, 

 is cooler than elsewhere in the state, a fact which may be more or 

 less intimately associated with the aspect of the vegetation there. 



1 Evaporation intensity as a determining factor in the distribution of vegetation 

 in Connecticut. Botanical Gazette. In course of publication. 



