METEOROLOGICAL CHARACTERISTICS. 289 



ferns and figs ; the sub-tropical zone, the region of laurels and 

 myrtles ; the warmer temperate zone, the region of broad-leaved 

 evergreen trees ; the cooler temperate zone, the region of decid- 

 uous trees ; the sub-arctic zone, the region of conifers ; the 

 arctic zone, the region of alpine shrubs, and the polar zone, the 

 region of alpine herbs. 



Massachusetts lies within the cooler temperate zone, which 

 is bounded on the north by the isotherm of 41° Fahrenheit, and 

 on the south by that of 54.5°. The average mean annual tem- 

 perature at Amherst, for the last thirty years, is 46.37°. This 

 is the region characterized by extensive forests of deciduous 

 trees in great variety, often intermingled with needle-leaved 

 evergreens. The plains when fertile are covered with rich 

 pasture grasses, and when barren with heather and other low 

 shrubs, while the swamps produce sedges and mosses, and con- 

 tain frequently deposits of peat. The climate is very intense, 

 and characterized by sudden and decided changes. The winters 

 are long and severe, with a mean temperature below 32° and 

 not unfrequently a depression of the thermometer to zero, and 

 even to 20° below. The ground is often bare during one-third 

 of the winter, and is consequently frozen to the depth of from 

 one to four feet. Since the trees are mostly stripped of foliage 

 and all herbaceous plants killed by the frost, the winter land- 

 scape presents a peculiarly dreary aspect, especially in the 

 absence of snow. This extreme severity of the cold season is a 

 great hindrance to the introduction of numerous desirable trees 

 and shrubs, to the growth of which the summer is well adapted. 

 The mean temperature of the three warm months is from 65° 

 to 70°, and there are often five months without frost. The 

 annual fall of rain and snow averages about 45 inches of water, 

 and the distribution of it through the year is tolerably uniform, 

 though droughts are not uncommon and occasionally injurious. 



Those plants which endure the peculiarities of the climate 

 without special care or protection are said to be hardy. It is 

 somewhat remarkable that science has thus far sought in vain 

 for any satisfactory explanation of the peculiar sensitiveness of 

 many species of plants to cold. The wood of the tender orange 

 tree is jjs close-grained and as hard as that of our evergreen 

 kalmias or rhododendrons, with similar leaves, and protected 

 from severe frost will ripen ks fruit and most of its young 

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