50 MASS. EXPERIMENT STATION BULLETIN 402 



2. Plant transpiration is the most effective mechanism returning moisture to 

 the atmosphere from the land^^; and the more cranberry vines, the more water 

 they take from the surface soil. 



3. Heavy vines suspend much of the water from rains so it evaporates very 

 readily. 



4. The more vines, the faster fallen cranberry leaves collect under them (pp. 61 

 and 63). 



Watching Frosts 



It is often best to watch developments when the bog temperature is likely to 

 approach the danger point. A night usually seems fully as dangerous as it is 

 when the first part is calm and clear, and often seems safer than it is when the 

 evening is windy. If it is very clear and calm till after midnight and a wind then 

 rises, it usually is a good sign that a helpful change is at hand, especially if the 

 barometer is falling, for the wind normally falls through the night and most in 

 clear weather. 



Conditions make it necessary to begin flooding some bogs early in the day be- 

 fore an expected frost, and it is always well to prepare for possible trouble by 

 filling bog ditches in the afternoon so as to be able to handle the situation prompt- 

 ly later if it gets too cold early in the night. More water may be put on in the 

 evening or during the night as circumstances require. The lowest bog temperature 

 usually occurs near sunrise. 



Weather Map 



Cranberry growers should subscribe for and learn to use the weather maps 

 published week days, except holidays, by the offices of the Weather Bureau at 

 Boston, Philadelphia, and New York. The most dangerous maps for Massachu- 

 setts, other things being the same, are those showing extensive high pressure over 

 the Great-Lakes region with low temperatures ahead of it in southeastern Canada, 

 New York, and New England and those with a strong high-pressure area ad- 

 vancing from the Hudson Bay region.^'' With the former, the general circulation 

 around the area of high pressure is sure to sustain the flow of cold air from the 

 north over New England and the rising pressure to slow the winds and sharpen 

 the cold; with the latter, there is usually such a quick thrust of a cold dry air 

 mass from the heart of Canada across New England that it is little changed by 

 insolation. 



Weather Instruments 



It is risky to use cheap instruments in frost observing. All bogs to be pro- 

 tected should have at least two standard minimum registering thermometers, 

 one to check the other. These are held by a metal bracket when in use, with the 

 bulb end a little lower than the other, the bracket being attached to a sharp stick 

 driven into the ground (Fig. 10). They are set by holding the bulb end up till 

 the glass indicator falls to the surface of the liquid in the channel. They must be 

 inspected frequently to make sure there is no break in the liquid column and there 



^^Thornthwaite, C. W., and Holzman, Benjamin, The determination of evaporation from land 

 and water surfaces, U. S. Monthly Weather Rev. 67:7, 1939 (copy in the Middleboro library); 

 Veihmeyer, F. J., Evaporation from soils and transpiration, Natl. Res. Council, Amer. Geophys. 

 Union Trans., 1938, 2:612-619. 



B^Smith, John W., Weather Forecasting in the United States, W. B. 583, 1916, pp. 169, 208. 



Such Hudson Bay air masses, though commonly very cold, persist over New England much less 

 often than those from farther west and rather rarely cause more than one cranberry frost. 



