. Bulletin of the Illinois State Laboratory of Natural History . at pulses at various seasonsof the year. There is little regularity in their duration oramplitude. When plotted from the means of the tri-dailyreadings of the air temperatures at Havana they do not ex-hibit delimitations as well defined as those, for example, of afully observed plankton pulse. Their amplitude, except inwinter months, rarely exceeds 20° between extremes, and theirduration is usually less than a fortnight between minima. Thatthese fluctuations affect the course of plankton production can-not be doubted. A detailed
. Bulletin of the Illinois State Laboratory of Natural History . at pulses at various seasonsof the year. There is little regularity in their duration oramplitude. When plotted from the means of the tri-dailyreadings of the air temperatures at Havana they do not ex-hibit delimitations as well defined as those, for example, of afully observed plankton pulse. Their amplitude, except inwinter months, rarely exceeds 20° between extremes, and theirduration is usually less than a fortnight between minima. Thatthese fluctuations affect the course of plankton production can-not be doubted. A detailed comparison of the course of produc-tion in 1896 and the thermograph of that year will show that,prcdommantUi, rises of temperature attend or precede rising pro-duction, while declines in heat are often correlated with de-creased production. This may be largely coincidence, or, insome cases, the common effect of cooler, barren flood-waters,especially in the case of the records of channel production. Aclose comparison, however, of the planktograph in Phelps 478. 479 Lake—where flood factors are largely excluded—and the ther-mograph (air) for 1896 will serve to suggest the possibility of acausal nexus between the two phenomena of fluctuations inheat and some of the movements in plankton production. Themany exceptions to any close correlation emphasize, however,the fact that heat is only one of the many factors involved inthe problem, and also indicate the necessity for much fullerplankton data, with closer interval and the proper quantitativerepresentation of the minute foruis now lost by leakage throughthe silk, for any adequate discussion of the problem. Thepresent data serve only to suggest the problem for investiga-tion. The effect of the ice-sheet upon the course of plankton pro-duction is apparent in a number of instances in our most noticeable case was the extermination of the plank-ton in the channel in February, 1895, by the ice-sheet of twomonths duratio
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectnatural, bookyear1876
