166 MASS. EXPERIMENT STATION BULLETIN 206. 



effects of that June's floodings on many other bogs were investigated, and 

 it was found that no notable injury had resulted anywhere except on bogs 

 that had been under water June 17. That day's flooding had done much 

 harm in all the five other cases found. It seemed, therefore, that there 

 was something peculiarly harmful about the weather of the 17th. As that 

 day had been darkly cloudy, comparative experiments in immersing vines 

 in water under shade and in sunshine suggested themselves. Many such 

 tests were made, pieces of cranberry turf with the vines being submerged 

 in some cases in tubs and in other cases in a pond. These tests took place 

 in late June and in July, the first vines being budded and partly in blossom, 

 and the last lots with the bloom gone and bearing small berries. The 

 immersion periods ranged from two to four days. The degree of shade 

 over the shaded lots varied in the different experiments, but in no case 

 did the light seem reduced as much as it is on a real cloudy day. In all 

 these tests the tender parts of the shaded vines were much hurt by the 

 submersion, while the vines immersed without shading were injured little, 

 the contrast between the shaded and unshaded vines in the tests in which 

 the shade was heaviest being striking. 



The uniform result of these experiments seems ample proof that the 

 continued reduction of light by cloudiness is harmful to cranberry vines 

 under water during their rapid summer growth. This being so, dark 

 swamp water is more likely to do harm than clear water, for it reduces 

 the light reaching the plants more; also deep flooding must be worse than 

 shallow, for the deeper the water the more light is cut off. These con- 

 clusions accord with effects of cranberrj^ flowage commonly observed. 

 Bogs flooded with dark water are oftener hurt than others, and Avhenever 

 a bog is hurt either by late holding of the winter water or by reflooding, 

 the parts most deeply submerged suffer most. 



Dr. H. F. Bergman of the Bureau of Plant Industry determined from 

 time to time the oxygen content of the water used in the immersion experi- 

 ments in tubs. In his papers on this work lately published, ^ he gives 

 what is probably the true explanation of the harmful effect of shading, by 

 cloudiness or otherwise, in summer cranberry flooding. Apparently the 

 injury is due to drowning of the more rapidly growing parts of the plant, 

 the oxygen in the water being reduced below the respiratory needs of these 

 parts too long. 



As Dr. Bergman shows, photosynthesis tends to keep up the oxygen 

 content of a bog flowage. One has onlj^ to see the many bubbles of oxygen 

 that form on the leaves of the flooded vines in clear summer weather to 

 appreciate this. As photosjmthesis depends on light, cloudiness greatly 

 reduces it or stops it entirely. On the other hand, respiration, the process 

 that uses up oxygen, goes on without regard to light. Apparently for this 

 reason cloudy weather is much more dangerous than clear weather for 

 flooding the bogs in their season of active growth. The days of the June 



» Ann. Rept. Cape Cod Cranb. Gr. Assoc, 1919-20, pp. 19-30. Amer. Journ. of Bot., 1: 50- 

 58, January, 1921. 



