WEATHER IN CRANBERRY CULTURE 11 



The Intensit}- of the light which passes through ice varies. The few measure- 

 ments made indicate that as much light penetrates a given thickness of clear ice 

 as of water. However, the ice on flooded cranberry bogs is seldom clear; snow 

 may become included in it when the ice is formed or afterward; and this reduces 

 the intensity of the light which passes through it, although often not in direct 

 proportion to the thickness of the ice since the amount of included snow varies 

 greatly and the more snow in the ice the less the penetration of light. Also, since 

 the amount of light lost by reflection from the ice surface becomes greater as the 

 distance of the sun from the zenith increases, the penetration of light on a clear 

 day is greatest at midday and diminishes progressively the earlier In the fore- 

 noon or the later in the afternoon the measurements are made. More light, also, 

 penetrates on a clear day than on a cloudy one. 



Less light penetrates ice with snow on It than when the snow melts into slush 

 and later freezes into the ice. No measurements have been made of light intensity 

 under Ice with a uniform snow cover, but a few measurements showed that only 

 one-fourth to one-third of the Incident light penetrated one inch of snow. The 

 penetration decreased rapidly as the thickness of the snow cover increased ; only 

 about 5 per cent of the incident light penetrated 4 inches of snow. 



In this connection reference should be made to the practice of sanding on the 

 ice. A layer of sand, even a quarter of an Inch thick, probably excludes all the 

 light from the vines, at least until the sand sinks Into the Ice as the ice melts. 

 Although sanding on the ice may be done a little more cheaply than by other 

 methods, there is a possibility that the shading effect may result in serious Injury 

 to the vines. The probability of injury appears to be greater if the sanding Is 

 done during December or January, when solar radiation Is lowest and cloudiness 

 is prevalent, than if done during the latter part of February or early in March, 

 when solar radiation is greater and the heat of the sun is absorbed by the sand 

 causing the ice to melt rapidly. 



Water colored by organic matter in solution also reduces the intensity of the 

 light received by cranberry vines at different depths in proportion to its color. 

 Though water used for flooding cranberry bogs is generally only slightly colored, 

 sometimes it is quite dark. Measurements show that on a clear day in June the 

 intensity of the light received by vines at a depth of 12 inches in "dark" water 

 may be as little as one-fourth to one-third of that received by vines in water only 

 slightly colored. 



Cloudiness, thick ice, and snow in or on the ice have but little effect on the 

 rate of respiration; consequently the amount of oxygen used daily in respiration 

 varies but little. On the other hand, these conditions, particularly snow on the 

 ice, often so greatly reduce the Intensity of the light received by the vines that 

 photosynthesis goes on very slowly, If at all, and little or no oxygen is given off. 

 If the amount of oxygen given off in photosynthesis during the short daylight 

 period of winter days is less than that used in respiration during an entire 24- 

 hour period, the amount of dissolved oxygen in the water will decrease from day 

 to day. It can increase only when less oxygen is used in respiration than is given 

 off in photosynthesis, and the rate of increase or decrease will be proportional to 

 the amount by which the oxygen given off is greater or less than that used. 



The Oxygen Requirement of Cranberry Vines 

 Under Winter-Flooding Conditions 



Cranberry vines require oxygen for respiration at all times, even in winter. 

 Respiration is greater in parts in which there Is greater physiological activity 

 as In the leaves and in parts of the terminal buds such as the flower buds, the 

 undeveloped new leaves, and the growing point of the uprights. Consequently, 



