BERKELEY LIBRARY UNIVERSITY OF CALIFORNIA SCIENCES LIBRARY UNIVERSITY OF CALIFORNIA OK C/^ss WISCONSIN GEOLOGICAL AND NATURAL HISTORY SURVEY. E. A. BIRQE, Director. BULLETIN NO. XII. SCIENTIFIC SERIES NO. 8 THE PLANKTON or f o Lake Winnebago and Green Lake BY C. DWIGHT MARSH Professor of Biology in Rifron College. MADISON, WIS. PUBLISHED BY THE STATE. October, 1903. WISCONSIN GEOLOGICAL AND NATURAL HJSIORY SURYEY. E. A. BIRQE, Ph.D. Sc.D., Director. BULLETIN NO. XII. SCIENTIFIC SERIES NO. 3. THE PLANKTON OF Lake Winnebago and Green Lake BY C. D WIGHT MARSH Professor of Biology in Ripon College. MADISON, WIS. PUBLISHED BY THE STATE. October, 1903. SCIENCE* LIBRARY Mteconsin Geological anD natural Distort Survey. BOARD OF COMMISSIONERS. ROBEET M. LAFOLLETTE, Governor of the State. CHARLES R. VAN HISE, President, President of the University of Wisconsin. CHABLES P. CABY, Vice-President, State Superintendent of Public Instruction. CALVEBT SPENSLET, President of the Commissioners of Fisheries. JOHN J. DAVIS, Secretary, President of the Wisconsin Academy of Sciences, Arts, and Letters. STAFF OF THE SURVEY. E. A. BIEGE, Director of the Survey. S. WEEDMAN, Geologist. Survey of Central and Northern Wisconsin. U. S. GEANT, Geologist. Survey of Southwestern Wisconsin. N. M. FENNEMAN, Geologist. Physical Geography of Lake Region. C. D. MARSH, Biologist. Biology of Lakes. L. S. SMITH, Civil Engineer. Survey of Lakes and Rivers. W. D. SMITH, Field Assistant. E. T. HANCOCK, Field Assistant. Consulting: Geologist. T. C. CHAMBBELIN, Pleistocene Geology. vim CONTENTS. Page CHAPTER I. OUTLINE OF STUDY 1-10 Lake Winnebago and Green Lake 1 Methods of making collections 8 CHAPTER II. ANNUAL DISTRIBUTION OF THE ORGANISMS OF THE PLANKTON , , ,. 11-46 Distribution of C. brevispinosus and C. pulchellus in Wiscon- sin lakes .• 27 The "bloom" 36 Annual distribution of the total plankton 38 Constituents which produce plankton maxima 39 Comparison of amount of plankton in different years 41 Comparison of plankton in Green lake and Lake Winnebago. . 42 Comparison with the plankton of other lakes 43 CHAPTER III. DISCUSSION OF RESULTS 47-59 Value of plankton collections 47 Relative importance of plankton constituents in producing maxima 49 Comparison of plankton and temperature curves 49 Comparison of curves of total plankton with curves of plankton contituents 51 Horizontal distribution 51 Comparison of plankton collections over muddy and stony bot- toms 59 CHAPTER IV. DISTRIBUTION OF SPECIES 60-69 Geographical distribution 60 Comparison of the faunae and florae of different classes of lakes 62 Comparison of plankton of successive years 65 Relative value of deep and shallow lakes for the production of fish 67 LIST OF PAPERS QUOTED 70-71 92 iv CONTENTS. Page APPENDIX. STATISTICAL TABLES 73 Table I. Total volumes of plankton per square meter in Green lake 73 Table II. Total volumes of plankton per square meter in Lake Winnebago 74 Table III. Total volumes of plankton per square meter in va- rious Wisconsin lakes 75 Table IV. Numbers of D. minutus and D. sicilis per square meter in Green lake 77 Table V. Numbers' of D. oregonensis per square meter in Lake Winnebago 78 Table VI. Numbers of E. lacustris per square meter in Lake Winnebago « 78 Table VII. Numbers of E. lacustris per square meter in Green lake 79 Table VIII. Numbers of L. rnacrurus per square meter in Green lake 79 Table IX. Numbers of C. brevispinosus per square meter in Lake Winnebago 80 Table X. Numbers of C. pulchellus per square meter in Lake Winnebago 80 Table XI. Numbers of C. leucfcarti per square meter in Lake Winnebago 81 Table XII. Numbers of C. prasinus per square meter in Green lake 81 Table XIII. Numbers of copepod larvae per square meter in Lake Winnebago 82 Table XIV. Numbers of copepod larvae per square meter in Green lake 82 Table XV. Nos. of Diaphanosoma brachyurum per square meter in Lake Winnebago 83 Table XVI. Numbers of D. hyalina per square meter in Lake Winnebago 83 Table XVII. Numbers of D. hyalina per square meter in Green lake 84 Table XVIII. Numbers of Bosmina per square meter in Green lake 84 Table XIX. Numbers of Eurycercus lamellatus per square meter in Lake Winnebago 85 Table XX. Numbers of Chydorus per square meter in Lake Winnebago 85 Table XXI. Numbers of Leptodora per square meter in Lake Winnebago 86 Table XXII. Numbers of Cypris per square meter in Lake Winnebago 86 Table XXIII. Maximum depth of Wisconsin lakes 87 INDEX.. 91 ILLUSTRATIONS. PLATE PAGE I. Curves of annual distribution of Gloiotrichia per square meter in Lake Winnebago ...... 6 II. Curves of annual distribution of Diaptomus sicilis and Diaptomus minutus per square meter in Green lake . 22 III. Curves of annual distribution of Diaptomus oregonensis per square meter in Lake Winnebago .... 23 IV. Curves of annual distribution of Epischura lacustris per square meter in Lake Winnebago 25 V. Curves of annual distribution of Epischura lacustris per square meter in Green lake 25 VI. Curves of annual distribution of Limnocalanus macru- rus per square meter in Green lake . , . . 26 VII. Curves of annual distribution of Cyclops brevispinosus per square meter in Lake Winnebago .... 26 VIII. Curves of "annual distribution of Cyclops brevispinosus per square meter in Green lake 26 IX. Curves of annual distribution of Cyclops pulchellus per square meter in Lake Winnebago .... 27 X. Curves of annual distribution of Cyclops Leuckarti per square meter in Green lake and Lake Winnebago . 28 XI. Curves of annual distribution of Cyclops prasinus per square meter in Green lake 29 XII. Curves of annual distribution of copepod larvae per square meter in Green lake 29 XIII. Curves of annual distribution of copepod larvae per square meter in Lake Winnebago 29 XIV. Curves of annual distribution of Diaphanosoma bra- chyurum per square meter in Lake Winnebago . 31 XV. Curves of annual distribution of Daphnia hyalina per square meter in Green lake 31 XVI. Curves of annual distribution of Daphnia hyalina and D. retrocurva per square meter in Lake Winebago - **-? VI ILL US TEA TIONS. PT.ATE XVII. PAGE Curves of annual distribution of JBosmina per square me- ter in Green lake 33 XVIII. Curves of annual distribution of Eurycercus lamellatus per square meter in Lake Winnebago .... 34 XIX. Curves of annual distribution of Chydorus sphaericus per square meter in Lake Winnebago .... 35 XX. Curves of annual distribution of Leptodora hyalina per square meter in Lake Winnebago . . . . . 36 XXI. Curves of annual distribution of total plankton in Lake Winnebago per square meter . .'„ . . . 38 XXII, Curves of annual distribution of total plankton, in Green lake per square meter . > • • • • . 38 THE PLANKTON OF LAKE WINNEBAGO AND GKEEN LAKE. CHAPTER I. OUTLINE OF STUDY. The attempt in this investigation has been to make a com- parative study of the plankton of two lakes of different types, with a collateral study of such other lakes as could be easily reached. It was thought that if , after a somewhat careful preliminary study, the plankton of the two lakes could be kept under observa- tion for a considerable period of time, many facts in regard to the annual and geographical distribution of the animals and plants could be secured, and perhaps some generalizations could be reached in regard to the principles controlling such distribu- tion. LAKE WINNEBAGO AND GREEN LAKE. Lake Winnebago was chosen for the type of the shallow lake mainly because of its importance from the standpoint of the pro- duction of fish. It is known to be an enormously productive body of water, and the fishing industry has employed a great many men in Oshkosh. letting has been forbidden by legisla- tive enactment for several years, and, in spite of many infrac- tions of the law, it is generally acknowledged among all but inter- ested parties, that the number of fish has greatly increased in 2 PLANKTON OF WINNEBAGO AND GREEN LAKES. that time. There is now hardly a better lake in the state for fishing for sport for some kinds of fish. The perch are espe- cially large and handsome, and the black bass are numerous and gamy, although rarely exceeding three or four pounds in weight. Pike, too, are caught in large numbers, and white bass are abun- dant in the spring. Lake Winnebago is some 28 miles long by 10 or 12 broad in its greatest width. There has never been an accurate hydro- graphic survey of the lake, but it is probable that it is nowhere over about 25 feet in depth. It is evident to a superficial ob- server that the plant life during the summer is very large, and it has been assumed that the abundant production of fish is correlated with the plant growth. The principal inlet of the lake, the Fox river, enters it about midway of the western shore, and leaves it as its outlet, at the northern end. Thus the lake may be considered simply as an expansion of the river. Connected with the Fox and its principal tributary the Wolf, is a number of lakes and streams which receive the drainage of a large section of the northeastern part of Wisconsin, extend- ing from the southern boundaries of Marquette, Green Lake, and Fond du Lac counties to the southern parts of Forest and Oneida counties. Many of these lakes are merely expansions of the rivers, and although covering areas of considerable size, are for the most part, very shallow. Lake Buttes des Morts, Lake Winneconne, Lake Poygan, and Lake Puckaway are the most prominent of these lakes ; their shores are for the most part low and swampy, and their depth rarely exceeds 10 or 15 feet. There are a few deeper lakes in this drainage area : Stone lake is between 75 and 80 feet in its greatest depth; the Waupaca lakes, though small in area, are in some cases from 60 to 95 feet in depth, and Green lake, with a maximum depth of 237 feet, is the deepest lake in the state. The deep lakes, as would be expected, are more distinctly cut off from the other parts of the drainage area than the shallow lakes. In the case of the shallow lakes, many open one into the other so that there is no distinct line of separation between OUTLINE OF STUDY. 3 them. It would be expected that this separation of the deeper lakes would have some effect on the character of their fauna and flora, besides the effect produced by the difference in envir- onment. The east shore of Lake Winnebago is, for the most part, high, and in some places rocky. At the south end the shore is swampy, — in fact it is rather difficult to distinguish between lake and shore. At this end the Fond du Lac river flows in, and there is a gradual encroachment of the shore line upon the lake. The west shore of the lake is low, but not, to any con- siderable extent, swampy, and is gradually being dotted over with summer cottages. At the north end of the lake are exten- sive sand beaches. The material of the lake shores is glacial drift, so that everywhere the shores are lined with boulders washed out of the drift by the waves. The bottom of the lake is generally composed of a fine mud filled with organic matter. In many cases, however, a bottom of boulders extends quite a distance from shore. Off Stony Beach this rocky bottom extended perhaps a half a mile from shore, and then is succeeded by a mud bottom without any dis- tinct change in depth. In other cases the bottom near shore is composed of sand or red clay. Before this work was undertaken, very little was definitely known of the plankton of Lake Winnebago. Only occasional collections had been made. It seemed necessary therefore to make a continuous series of collections lasting over a consider- able period in order to get a basis of comparison. It was neces- sary, too, that there should be an opportunity to examine the living collections, as many things are sure to be overlooked in preserved material. Accordingly a summer station was established at Stony Beach, a small summer resort about two miles south of Osh- kosh. Comfortable quarters were found in an old hotel build- ing, the dining room being fitted up as a laboratory. The laboratory equipment and a working library were brought from Eipon College. A row boat was provided for the regular daily work, and, through the kindness of Mr. Chas. Schreiber of Osh- 4. PLANKTON OF WINNEBAGO AND GREEN LAKES. kosh, we had the use of a sail boat for longer trips. Through the courtesy of Mr. M. W. Feck and Mr. D. Jack of Fond du Lac, we were provided with transportation in their gasoline yacht for an extended trip through Lakes Buttes des Morts, Winneeonne, and Foygan. Acknowledgment should be ren- dered, too, for unnumbered services rendered by Mr. D. O. Fernandez of Oshkosh. The location proved to be particularly convenient, as Stony Beach is reached by an electric line from Oshkosh and yet is so far removed from the city that under ordinary conditions it is not probable that this part of the lake is contaminated by the city sewage. Systematic work on Lake Winnebago was commenced the fifth of July, 1899. During July and August, with the excep- tion of a few days spent on other lakes, daily plankton collec- tions were made at at least two locations. For these daily col- lections a station was selected about a mile from the shore on the muddy bottom common to all the deeper parts of the lake, and another nearer shore on the rocky bottom. This was with a two-fold object, first to have two stations some distance apart in order to get an average of plankton, and second to! determine whether there was any decided difference in the plankton over the mud and over the rocky bottom, for the fishermen think that some fish have a decided preference for the stony bottom. Some days a considerable number of collections was made, the locations being widely distributed over the lake. During the summer the collections extended over a distance of some twelve or fourteen miles on the west shore of the lake; many were made in the central region of the lake, and some on the east shore. A number of collections, for comparison, were made on other lakes synchronously with those on Lake Winnebago, my assist- ant remaining on that lake while I did the work at other loca- tions. After the month of August the collections were kept up at intervals of about two weeks, the collections being made ordinarily at the two regular summer stations off Stony BeacL OUTLINE OF STUDY. 5 These collections were continued through a period of two years and a half. Collections at a similar interval of two weeks were also made on Green lake. Green lake was selected for comparative work, partly because of its convenient location, but mainly because its conditions are so different from those of Lake Winnebago>. Green lake is situated in Green Lake county, about 25 miles west of the southern end of Lake Winnebago. It is about 7% miles long, with a maximum width of 2 miles. Nearly the whole lake is over a hundred feet in depth, and the western part has a maximum depth of 237 feet. The shore slopes are, for the most part, very abrupt, only a small part of the shore being swampy. The waters of Green lake are exceedingly clear, rarely being markedly discolored by vegetable growths, while in Lake Winnebago during most of the year the water is much dis- colored. On account of the small depth, of Lake Winnebago, storms disturb its water to the very bottom over most of its area, while in the depths of Green lake there is a large body of water which is never appreciably affected even by the severest storms. Because of its depth Green lake has a distinct uthermocline" during the summer months, and the water at the bottom has an annual range of temperature of only about ten degrees Fahren- heit. Lake Winnebago, on the other hand, has, during the sum- mer, a, nearly uniform temperature from top to bottom. Lake Winnebago, because of its slight depth, and the fact that the whole body of water is so easily affected by storms, becomes wanned much earlier in the spring than does Green lake, and cools off with corresponding rapidity in the fall. The result is that Lake Winnebago is covered with a thick coat of ice long before Green lake is frozen over. Green lake is seldom covered with ice before the first of January, and parts of the lake sometimes remain open through the whole winter. As a result of the late freezing, the ice never reaches the thickness on Green lake that it does on Lake Win- nebago. Because of its great depth, and the consequent exist- ence of a thermocline in Green lake in summer, this body of water has a true "abyssal" fauna, organisms which can exist 0 PLANKTON OF WINNEBAGO AND GREEN LAKES. only in the peculiar environment of uniform low temperature and little or no light. Lake Winnebago, on the other hand, can- mot be said to have an abyssal fauna, the animals of the bottom in the deeper parts of the lake not differing appreciably from those of the littoral region. With such differences in physical conditions we should ex- pect corresponding differences in fauna and flora. The writer has already suggested in a former publication (Marsh 797, 181) that lakes may be divided into the two classes of "deep" and "shallow," the dividing line between the two classes being at about forty meters. Later (Marsh, ?99, 171) I was led to think that the limit should be placed at a lower figure, — per- haps thirty or thirty-five meters. It would be better, doubt- less, to make the main classification of lakes depend upon the existence or non-existence of a thermocline. In the shallow ]akes there is no thermocline. Taking the presence or absence of a thermocline as the basis of classification, the depth limit between deep and shallow lakes would not be definite but would bear a constant relation to the area and character of the shore ; for the thermocline is much more marked in small lakes with high shores. Deep lakes are susceptible of a two-fold classification into the large and the small. In the small deep lakes the abysssal water stagnates, and the conditions of life become so hard that an abyssal fauna can hardly be said to exist. In the large deep lakes, on the other hand, the movement of the surface waters under the influence of the winds produces slow return currents along the bottom which serve to relieve the condition of stagna- tion, and permit the existence of a somewhat abundant abyssal fauna. Green lake and Lake Geneva have the characteristics of large deep lakes, while Elkhart and the Waupaca lakes are types of small deep lakes. On the whole this seems to me the most satisfactory classi- fication of lakes, and in this paper I shall use the terms "deep," "shallow," "large deep," and "small deep," as indicated above. While, as will be seen later, faunal and floral distinctions do -- (0 GO O CD O CO OUTLINE not follow absolutely this classification, yet they have a close relation to it. Green lake may be considered the typical deep lake of Wis- consin, and, as observations have been carried on upon its fauna and flora for a number of years, it was natural to select it for comparison with Lake Winnebago. Collections were made on as large a number cf lakes in other localities as time would permit. Some of these lakes were se- lected because they had apparently different conditions from those prevailing on Lake Winnebago and Green lake, but others were taken for the express reason that their conditions seemed to resemble very closely those of the lakes which were made the standards of work. Inasmuch, as will be shown later, experience has shown that plankton collections are really significant only as averages can be obtained of a considerable number of collections, and that single collections may be very misleading, so far as possible an attempt was made to visit a certain number of lakes repeatedly, rather than to make a large number of single collections from different bodies of water. Unfortunately the time at command did not permit of as many of these trips as was desirable, so that in some cases single collections only could be made: as it was important that there should be as wide a basis of com- parison as possible, it seemed better to make these single collections than no collections at all. The author clearly recog- nizes, however, that it would have been much better had it been possible to work a circuit of a considerable number of lakes continuously. If lakes could be classified into a series of a few types, of course, it would be necessary only to take one of each type. But, so far, no entirely satisfactory classifica- tion, from the standpoint of the fauna and flora, has been pro- posed, so that one can not be certain when he limits his work to a few lakes, that he may not miss some important principles of distribution which are only exemplified in the bodies of water which he has not examined. Four somewhat extended trips, in four successive years, were made to lakes in the forest region of Wisconsin, including lakes 8 PLANKTON OF WINNEBAGO AND GREEN LAKES. in Shawano, Forest, Oneida, and Langlade counties. The first of these trips was made in September, the last three in the mid- dle of August. To some of these lakes visits were made at other times. Such collections, as intimated before, while giv- ing a very imperfect idea of the f aunal and floral conditions of these bodies of water, are yet very valuable as a matter of com- parison. In this work the objects kept in view have been the following: 1st. Lists of the fauna and flora. Inasmuch as the work has been done entirely by one person, with the aid of an as- sistant for a part of the time, and my exact systematic knowl- edge is very largely confined to the entomostraca, it is not to be expected that this list will be complete. It will, however, serve to show such important differences as may exist between the fauna and flora of Lake Winnebago, Green lake, and the other lakes. 2nd. A quantitative study of the plankton which should give a clear idea of the annual variations, and of the quantita- tive difference between the plankton of Lake Winnebago and Green lake. 3rd. A qualitative study of the plankton in order to deter- mine the variations in its components in the course of the year. 4th. It was hoped that the studies of the above topics would furnish material for some exact additions to our knowledge of the distribution of the animals and plants of the plankton, and might help in the solution of the very complex problem of the relation of the plankton to the fish. METHODS OF MAKING COLLECTIONS. In settling upon the methods which should be used in mak- ing the collections, it was necessary to choose a method which would be practicable in a permanent station, and yet which should not involve so cumbersome apparatus that it could not readily be carried from place to place without making too much of a burden of weight. This latter consideration made the pump impracticable. Moreover, I am inclined to agree with OUTLINE OF STUDY. 9 the conclusions reached by Reighard (Reighard '98) that it is very doubtful if the pump gives one a representative collection of a column of water. In deep waters, of course, the pump in- volves very unwieldy apparatus. In shallow waters, especially for making collections at specific levels, the pump is a useful adjunct to plankton apparatus. In the opinion of the author no method has yet been devised that serves the purpose so well as a vertical net. It is very much to be desired that the net should have a wide opening, as is stated by Reighard. Port- ability was so necessary in my case, however, that size had to be sacrificed. The undoubted fact that nets vary in their collect- ing ability because of the clogging of the meshes, especially in silt laden waters, was deemed in these researches as of minor importance, partly because the waters examined were for the most part fairly clear, and partly because, as will be seen later, the author attaches very little importance to exact measure- ments of the plankton, but relies for results on averages. The net used was of the pattern of Hensen, the upper cone being of copper, with an opening 10.5 cm. in diameter. The net was of bolting silk, attached below to a removable bucket, of a form devised by Professor Birge. The net was drawn from the bottom to the surface, the net washed down from the outside, and the bucket, by the aid of a wash bottle filled with alcohol, emptied directly into the collecting bottle. I made it a rule to make three collections at each station, and in stating results the three collections were averaged. To determine the gross amount of plankton it was decided to use the centrifuge. The objections to the method of settling in graduated tubes have been well stated by other authors. (Ward '95, Kofoid '97.) The lack of exactness in plankton measurements does not warrant the labor of the gravimetric method. It was decided to use the centrifuge, as being the best method yet devised. For this purpose the ordinary uri- nary centrifuge was used, with tubes graduated to tenths of a centimeter. After a little experience it was decided to ran the centrifuge in the following way: 1st, two revolutions of the crank ; 2nd, two revolutions in the reverse direction ; 3rd, a 10 PLANKTON OF WINNEBAGO AND GREEN LAKES. continuous run of % niin. ; 4th, y2 min. in the opposite direc- tion ; 5th, one minute straight ahead. The centrifuge was run at from 1200 to 1500 revolutions per minute, any greater rapidity heing almost certain to break the tuhes. It was found that the work was most successful when the percentage of alco- hol in the collected material was rather high. This method has some inaccuracy, as well as the method by settling, for the different kinds of material are not equally well thrown down. Some of the algae, in spite of long continued running of the centrifuge, will always lie in a more or less flocculent mass on top, and in some cases, even after being thrown down, will afterwards rise into the supernatant liquid. The supernatant fluid, even when apparently perfectly clear, always contains a little of this plant material. The amount is so small, however, that it has no evident effect on the measurements of the plank- ton. The examination of the plankton was by the method ex- plained in my former paper. (Marsh '97, p. 188.) At first all the counting was done by means of the dissecting lens, but later, for the smaller forms, a compound microscope was used, with a stage especially arranged to receive the counting plate. Only the Crustacea were counted exactly, with the exception of Gloiotrichia, of which a, careful count was made. But notes were mad© of the occurrence of the other forms and a rude esti- mate of the numbers made and recorded under the terms "few," "many," "very many," and "nos." ANNUAL DISTRIBUTION OF THE ORGANISMS. CHAPTER II. ANNUAL DISTRIBUTION OF THE ORGANISMS OF THE PLANKTON. Asterionella gracillima Heib. Asterionella occurs in both lakes through the entire year. In Lake Winnebago there seems to be a minimum in June, July, and August, but no very pronounced maximum period. In Green lake there is a similar paucity of numbers in the summer months and a strong maximum in February, March, and April. This winter maximum was first noticed in 1900 when Asterionella was found in such numbers as to make a layer of water two feet in thickness almost opaque, — the water having a milky appearance. This winter increase was con- firmed in the two succeeding winters, and it would seem to be a fair inference that its maximum in Green Lake occurs regu- larly in the winter. Cyclotella flocculosa (Koth) Kg. Cyclotella is never found in any numbers in Green lake. I have found it only in November, January, February, and May. In Lake Winnebago, in the years under observation, Cyclo- tella was at its maximum of development in the fall months, September, October, and November. In 1900 there was an in- crease in May, and in 1901 in the last of April. I think, then, that we may say that Cyclotella in Lake Winnebago has two maxima, the principal one in the fall with its greatest develop- ment about the first of November, and the other one less pro- nounced about tbi> first of May. 12 PLANKTON OF WINNEBAGO AND GREEN LAKES. Melosira. Melosira is found in very small numbers in Green lake, and no inferences can be drawn as to its annual distribution. In Lake Winnebago its appearance seems somewhat erratic, but there is evidence of two maxima, one in May, and one in September. Synedra, pulchella Kiitz. Synedra pulchella occurs in Lake Winnebago in 'all the months of the year. In 1900 there was evidence of a spring maximum in May and a fall maximum in October. In the other years there was no pronounced increase at any time. In Green lake it is practically absent in July and August, and only few are found in September, October, and Novem- ber. Large numbers are present in December, January, and February, and there is another increase in April and May. Synedra acus var. delicatissima Grun. This variety occurs in both Green lake and Lake Winnebago, but in much greater abundance in Green lake. I have found it in Lake Winnebago in February, March, April, and June. In Green lake I have found it in nearly every month of the year, but it is in the winter that it especially flourishes, being very numerous from January to May. With Asterionella it forms one of the most important elements of the winter plank- ton of Green lake. Fragilaria. I have not found Fragilaria in Lake Winnebago in July, August, September, or October, and only once have I found it at any time very abundant, — that was in the middle of May, 1900. In Green lake it occurs at the same times, my only large col- lection being at the middle of May, 1901. ANNUAL DISTRIBUTION OF THE ORGANISMS. 13 Stephanodiscus. Stepharwdiscus I have not found at all in Green lake. In Lake Winnebago it may occur from February to July, with a maximum at some time in the spring. In 1900 there were two important periods of large numbers, one the middle of May, and one the last of June. In 1901 the first increase came the last of April and the second the first week in June. Other diatoms were noticed in the plankton, but none in suf- ficient numbers to be of any importance in the total amount. Navicula. Navicula was found in Green lake a few times and occurred in Lake Winnebago in many of the collections, especially in the winter months. Surirella and Pleurosigma. Surirella and Pleurosigma were found a few times in Lake Winnebago. Nassula. Nassula, also, was noted in the flora of Lake Winnebago. COMPARISON OF RESULTS ON ANNUAL DISTRIBUTION OF DIATOMS WITH WORK OF OTHER AUTHORS. I find very few recorded facts in regard to the annual dis- tribution of the various genera of diatoms. Apstein (Apstein '9 6) finds the two maxima of Melosira much as I do. His maxima for Asterionella do not correspond to my results. Whipple (Whipple ?94), in a discussion of the growth of diatoms in surface waters, comes to the conclusion that the growth of diatoms is directly connected with the phenomena of stagnation, that in deep ponds there are two well defined periods of growth, — one in the spring and one in the fall : that in shallow ponds there is usually a spring growth but no regu- 14 PLANKTON OF WINNEBAGO AND GREEN LAKES. lar fall growth, and that other growths may occur at irregular intervals as the wind happens to stir up the water ; that the two most important conditions for the growth of the diatoms are a sufficient supply of nitrates and a free circulation of air, and that both these conditions are found at those periods of the year when the water is in circulation. Whipple gives facts in re- gard to the annual distribution of diatoms in Massachusetts ponds which seem thoroughly to substantiate his contention, I have already referred to this work in a former paper (Marsh '99 ), accepting these conclusions. In looking over the occur- rence of the diatoms in Green lake and Lake Winnebago I find nothing to contradict this theory in the occurrence of Cyclo- tella, Melosira, Synedra, Fragilaria, or Stephanodiscus. The occurrence of Cyclotella in Lake Winnebago especially seems to confirm his statements. The occurrence of Asterionella in Green lake, however, dif- fers distinctly from his results in Massachusetts waters. His general conclusion in regard to Asterionella is that its two max- imum periods come after the spring and fall overturning when the spores, — if diatoms have spores, — are brought to the sur- face accompanied by the food materials that have been forming in the abyssal waters during the stagnation period. Now in Green lake the maxima, as found in three winters, came in the depth of winter when the lake was covered with eighteen inches or more of ice, and at a period midway between the two overturnings of the water. It is evident that Whipple's ex- planation does not apply in this case. Why there should be this enormous production of Asterionella in mid-winter I do not at all understand. Yoigt (Voigt '02) reports Asterionella as having a similar winter maximum in Trammer-See and Ede- berg-See. Closterium. Two or three species of Closterium occur in both lakes as occasional members of the plankton. They cannot be considered as true limnetic species, but rather as migrants from the littoral flora. ANNUAL DISTRIBUTION OF THE ORGANISMS. 15 Pediastrum. I have found Pediastrum in Lake Winnebago in every month of the year except March and April. It is most abundant in the summer and fall months but seems to have no pronounced maximum. S taurastrum*. Staurastrum is found in Lake Winnebago from May to No- vember but never in any considerable numbers. s Eudorina. Eudorina I have found in small numbers in June and July. Merismopedia. Merismopcdia was found in small. numbers through the sum- mer and fall of 1899 in Lake Winnebago. In 1900 it was found only in the fall months, continuing to the middle of Feb- ruary. In 1901, too, it did not appear until fall except in a single collection in June. Clathrocystis aeruginosa Henfr. I have never found Clathrocysiis in the plankton of Green Lake. In Lake Winnebago it occurs throughout the summer, appearing as early as June, and sometimes remaining as late as October. I have found it in great numbers in Lake Buttes des Morts in August. It appears in the same month in Peli- can lake and the Eagle River lakes. It does not appear to be a constituent of the plankton in the deeper lakes. Anabaena. Andbaena is one of the most important constituents of the summer plankton. It occurs in Green lake, sometimes in noticeable amount, so that little ridges of it are thrown upon the shore by the waves. It is in the shallow lakes, however, that it nourishes in especial abundance. It appears in Lake Winnebago as early as May, and may be found as late as Octo- 16 PLANKTON OF WINNEBAGO AND GREEN LAKE 8. ber. It reaches its greatest abundance in July and August. The numbers in September are ordinarily very small. Yet I have found it in Pelican lake in great numbers in the latter part of September. Aphanizomenon. ApJianizomenon occurs in Lake Winnebago associated with Anabaena, its period of growth being very similar although it does not appear so early nor remain so long. While I have not counted Anabaena and Aphanizomenon , and so cannot state their maximum period with any exactness, I get the impression that Anabaena reaches its maximum earlier than Aphanizomr enon. It is found in other shallow lakes associated with Ana- baena. Oscillaria. Oscillaria is not a constituent of the plankton in either Green lake or Lake Winnebago. In some of the shallow lakes, how- ever, it is very abundant at certain times in the summer. This is notably so in Shawano lake where it seems to assume the importance that Anabaena and Aphanizomenon do in Lake Winnebago. Lingbyj,. Lingbya is associated with Anabaena and Aphanizomenon in Lake Winnebago, especially in July, sometimes in large numbers, but is of less importance than the other two genera. Gloiotrichia echinulata Richt. Gloiotrichia has no importance in the plankton of Green lake. In Lake Winnebago it is found in great numbers in July and August. In the summer of 1899 (Plate I) there was a rapid increase from the first of July to the middle, fol- lowed by a decrease, from which there was again a -rise to a maximum about the twelfth of August. In 1900 there was a single maximum early in July. The total production of GloiotricJiia in 1899 was much greater than in 1900. ANNUAL DISTRIBUTION OF THE ORGANISMS. tf The collections of Gloiotrichia. in the other lakes of the state were made on only a few dates so that a comparison of num- bers would be subject to revision after a more complete knowl- edge of those lakes. So far as appears, however, Gloiotrichia occurs ir vastly greater abundance in Lake Winnebago than in. the other bodies of water from which collections were made. The only exception to this was a very large collection of Gloiotrichia made on Pelican lake August 12, 1902. Other collections made on Pelican lake in preceding years, however, did not indicate so large a production of this plant as in Lake Winnebago. Sphaerella lacustris (Girod) Wittrock. This organism I have found a fairly constant constituent of the plankton of Green lake. During the first year it occurred in the collections from September until the next June. Dur- ing the second year it was found from early in August until the last of December. In the third year it appeared through the fall months, and after that the collections were discontinued. Its maximum of appearance seems to be from September to January. In Green lake it seems to be distinctly characteristic of the cold season. I have not found this form in Lake Winnebago, but it does occur in a number of the other lakes, generally in small num- bers, but in August, 1900, I found large numbers in Shawano and Pelican lakes. Although it is found in the plankton more in the colder sea- son, it does not follow that it lives in Green lake only at that time, for I have found it in enormous numbers in Dartford Bay in boats that were standing half full of water in the summer. Dindbryon. Dinobryon occurs in both Green lake and Lake Winnebago. In Green lake the largest collections have been in May, June, and July, but it may occur in any month. In Lake Winnebago I have never found it in July and Au- gust, but it comes in with September, is found in small numbers 15 PLANKTON OF WINNEBAGO AND GREEN LAKES. in the fall and winter, and reaches a maximum of numbers in Miarch. In the European lakes, according to Apstein and Zacharias, this genus occurs from April or March to August, but it would appear from my collections that it may be found in our lakes at any time except that in Lake Winnebago it fails at the hottest time of the year. It would seem to be a fair presumption that the heat of mid-summer is unfavorable to its growth although it has been found in Green lake in great numbers in July. Synum uvella Ehrenberg. I have found Synura in Green lake only in two collections made in May, 1901. In Lake Winnebago it sometimes forms an important ele- ment in the winter plankton. I have found it in the months f romi November to April, with the largest nuanbers in January, February, and March. It seems to be very distinctly confined, in its development, to the months when the lake is covered with ice. Uroglaena. I have not found Uroglaena as a constituent of the plankton of either Green lake or Lake Winnebago. I did find it, how- ever, in large numbers in the plankton of the Eagle River lakes in 'August, 1901 and 1902, and it seems probable that in some shallow lakes it may be in the summer an important element in the plankton. Cemiium Jiinmdinella 0. F. Miiller. Only once did I find Ceratium in Lake Winnebago in any considerable numbers, — in a collection made August 22, 1900. It cannot be said ever to form an important part of the plank- ton of this lake. It may be found at almost any time of the year but always in small numbers. In Green lake it is distinctly a summer form. It is almost entirely absent except in the months from July to October, in- clusive. In the summer of 1899 its maximum was reached ANNUAL DISTRIBUTION OF THE ORGANISMS. ^9 the last of July, in 1899 its greatest development was early in October, and in 1901 it reached a maximum about the mid- dle of September. The total production in 1901 was much greater than in the preceding years. Codonella lacusiris Entz. Codonella does not occur in Green lake. In Lake Winne- bago it is found most abundantly in the winter months, although it occurs at other times of the year. It is never pres- ent in sufficient numbers to affect the total plankton. Epistylis galea Ehrenberg. Epistylis was found in small numbers in the plankton c^. Lake Winnebago in the fall of 1900 and 1901. I found it also in the plankton of Birch lake in August, 1900. Anuraea coclilearis Gosse. Anuraea cochlearis is found at all times of the year in both lakes. There is no uniform maximum period. Apstein states for Plb'ner See that the greatest numbers are found in July. Seligo finds for various lakes maxima in May, June, July, and September. The largest single collection in Green lake was made in Au- gust, while the largest collection in Lake Winnebago was made in January. The occurrence of the species, however, was very erratic, and I can draw no conclusions as to its annual period- icity. Anuraea aculeata Ehrenberg. Anuraea aculeata was found in Green lake only in two col- lections,— in July and December, 1901, and then in very small numbers. In Lake Winnebago it was pretty constantly in the plankton from October or November until the next May. The largest single collection was in January, 1900. Thus Anuraea aculeata would appear to be a distinctly winter form. Tnis agrees with the statements of Seligo and Voigt, but Apstein has found it a summer form. 20 PLANKTON OF WINNEBAGO AND GREEN LAKES. I have, however, found it in other lakes in the summer. It occurred in August, 1901, in both Shawano and Stone lakes in small numbers. In August of both 1900 and 1901 it was found in large numbers in Birch lake, I have found it also in Cedar lake in March and June. It is evident then that Anuraea aculeata may occur at any time of the year, and I see no reason why in Lake Winnebago it should be limited to the colder months, for the conditions of Shawano lake are very similar to those of Lake Winnebago. Anuraea quadridentata Ehrenberg. Anuraea quadridentata I have not found in Lake Winnebago. It appeared in Green lake in 1901 from February through the month of April. Polyarthra platyptera Ehrenberg. Polyarthra is a perennial form in Lake Winnebago. Gen- erally speaking the numbers are greater from July to October, but in one year there was a very large production in February and March. In Green lake it occurs from June through the month of October. I have never found it in the winter months. The European authors speak of Polyarthra as a perennial. The occurrence in Green lake would seem to be somewhat pecu- liar, and I cannot see what circumstances in Green lake should be more unfavorable to it than in Lake Winnebago. Triarthra longiseta Ehrenberg. Triarthra is never found abundantly in either lake. In both it is found from June to November, and only occasionally in the winter months. Notholca longispina Kellicott. NotJiolca longispina is much more numerous in Green lake than in Lake Winnebago. In both lakes it may occur at any time of the year, with no pronounced maximum period. The largest single collection in Green lake was in February, 1900. ANNUAL DISTRIBUTION OF THE ORGANISMS. 21 In general, the collections of the fall and winter months were larger than those of the summer. The conditions of a deep lake seem to he more favorable to the production of NotJiolca longispina than those of a shallow one. Seligo states that it was found in greater numbers in the deeper of the Stuhmer lakes. NotJiolca foliacea Ehrenberg. Notholca foliacea is not a common member of the plankton of these lakes. T have found it in Green lake only once, on May 4, 1901. In Lake Winnebago I found it in collections made in the middle of February and in the middle of March, 1901. Asplanchna sp. An undetermined species of Asplanchna was found in Green lake in January and March, 1900. In the same winter it was found in Lake Winnebago as early as November and was a fairly constant member of the plankton until the middle of March. Syncliaeta pectinata Ehrenberg. Synchaeta pectinata occurred in Green lake in the winters of 1900 and 1901. In the winter of 1900 it was found in the months of February, March, and April. In 1901 it was found from January to March. It was found in a single collection also in October, 1900. In both winters the largest numbers were in the collections made on the twenty-third of February. In Lake Winnebago it is also a winter form with a somewhat more extended period of occurrence than in Green lake. I have found it in the months from October to April, inclusive, and in a single collection in June, 1901. This occurrence of Synchaeta pectinata corresponds fairly well with the results obtained by European investigators. Ap- stein finds it a perennial form, with its maximum in the win- ter months. He states, however, that in his counting he has not distinguished the species of Synchaeta, and it would seem possible that pectinata did not occur in the summer months. 22 PLANKTON OF WINNEBAGO AND GREEN LAKES. Seligo says that S. pectinata occurs through the whole year with a maximum in September. Voigt (Voigt '02 ) says that 8. pectinata is generally absent in the summer months, but is found in the fall, winter, and spring, while other species occur in the summer. Conochilus volvox Ehrenberg. Conochilus was found in Lake Winnebago in the summers of 1899 and 1901. In 1899 it reached its greatest numbers in the last week in July. In 1900 I found the largest numbers July 9. In 1900 a few were found in October and November. I have not found it in any of the collections from Green lake, nor does it seem to be distributed very generally in other lakes. In September, 1899, I found it in Birch lake, in June, 1900, in Cedar lake, Washington county, in August, 1900, in Pelican and the Eagle River lakes, and in August, 1901, in consider- able numbers in one of the Clover Leaf lakes. While it is not at all uncomimon in the summjer months, its distribution seems to be somewhat erratic. Apstein finds a much longer period for Conochilus, but states that it is irregular in its maximum period. Voigt (Voigt '02) states that the period for Conochilus vol- vox extends from August to November, but other species of Conocliilus may occur in the winter months. Diaptomus minutus Lilljeborg and sicilis Forbes. D. oregonensis does not occur in Green lake but its place is taken by D. minutus and D. sicilis. In a former paper (Marsh 79T) I discussed the annual distribution of these Diap- tomi, and the curves given in Plate II, while they modify the conclusions reached at that time, do not do so in any material way. As in my former work, I did not in the counting dis- tinguish between the two species, but, in every case, careful ex- amination was made as to the presence of the two species. I have very little to add to the statement already made (Marsh '97, 193) in regard to the annual distribution of these two species. D. minutus occurs in the months from July to Decem- S "H. — ? ~| ?l §,*§ y. -: HH Ld m *S P < 8 5 0) 0) 85 0) 0) ANNUAL DISTRIBUTION OF THE ORGANISMS. 23 ber, inclusive. D. sicilis is found from the last of September or first of October until the first of July. D. sicilis is rarely present in the summer months as D. minutus is seldom found in the. winter and spring months. In considering the curve, then, it must be remembered that the summer maxima are for minutus while the winter maxima are for sicilis. In Novem- ber and December and again the last of June the species are found together in the plankton. In the three years under ob- servation the greatest production of minutus was not far from the first of August with a smaller fall maximum the last of September or first of October. This differs from the only com- plete curve in my former paper in that then the greatest maxi- mum was in September. D. sicilis reaches its greatest numbers in February and March. It may be remarked that this maximum of D. sicilis corre- sponds with the maximum period of development of Asterio- nelldj but whether there is any causal relation between the two I am unable now to say. Diaptomus oregonensis Lilljeborg. Diaptomus oregonensis is the only form of the genus found in Lake Winnebago, and is the common form in the greater majority of Wisconsin lakes. The curves of annual occurrence are shown in Plate III. It will be noticed that in the first summer there were three marked maxima, the last of July, the middle of September, and the first of November. There was then a rapid decline, a constant winter minimum during January, February, and nearly through the month of March, when there commenced a slow increase in numbers. In the second year the maxima were in the middle of August, the early part of November, and a heavy maximum in the next June. In the third year the summer maximum occurred the first of September with a fall maximum the early part of No- vember. In comparing the three years the uniformity of the November maxima is very remarkable. With the July maxi- mum of 1900 there is nothing to correspond in the other years. 24 PLANKTON OF WINNEBAGO AND GREEN LAKES. We can say, in general, that Diaptomus oregonensis occurs in its greatest abundance during the months from June to Novem- ber, inclusive, that it is found only in very small numbers from the latter part of November until the last of March; that it has a constant fall maximum and one or more mid-summer maxima which occur between the last of July and the first week in September. So far as I know there are no preceding obser- vations on the annual periodicity of D. oregonensis except those recorded by Birge (Birge 79T). The curves of D. gracilis and D. graciloides as recorded by Apstein, Steuer, and Seligo correspond in general with these curves, but differ in details. Especially noticeable is the state- ment of Apstein that the maximum of D. graciloides in Lake Plon occurs in the winter. In comparing my results with those of Birge, while there is a general resemblance in the curves, there are certain marked differences. He states that in Lake Mendota the smallest catches of the year were made in the latter part of April, and he infers that the conditions of life are harder for them after the going out of the ice. In Lake Winnebago there was a distinct increase during the month of April with a drop during the first half of May. I am unable to explain this increase, but it does not appear that the going out of the ice worked any hardship in the case of the Lake Winnebago Diaptomus. In Lake Mendota there seems to have been no increase corre- sponding to the November maximum of Lake Winnebago. It is possible that this fact has some bearing upon the question of the effect of temperature upon the species. Birge (Birge '97, 326) states that the reproduction of D. oregonensis is more promptly checked by a fall of temperature than is that of any other species. Of course there is no question of the truth of the general proposition that the reproduction of this Diaptomus is dependent upon higher temperatures. The general charac- ter of the curves shows that at once. If, however, it were par- ticularly sensitive to a decline in temperature, should we not expect fall reproduction to stop soonest in the lake that cools off the most quickly? Lake Mendota has a maximum depth 0) O> ANNUAL DISTRIBUTION OF THE ORGANISMS. 25 of about eighty feet, while the maximum depth of Lake Win- nebago is only about twenty-five feet, and because of its greater extent is doubtless much more affected by the winds. It seems to me that if the species were especially sensitive to tempera- ture we should expect the fall maximum in the deeper lake rather than in the shallower, as seems to be the case. Epischura lacustris Forbes. Epischura is distinctly a summer form. As shown in the curves (Plates IV and V) it appears sometimes as early as May and may be found as late as December or even January. In Green lake the larval forms appear in February and March. This is not indicated on the curves of the Epischura plate, as in the counting the Epischura larvae were not distinguished from those of the other copepods. The period of maximum devel- opment occurs in July or August. It will be noticed that the spring increase occurs a little later in Green lake than in Lake Winnebago, and that the summer maxim am of Green lake is also a little later than that of Lake Winnebago. Epischura remains in Green lake, too, later into the fall than it does in Lake Winnebago. This is without doubt due to the fact that Green lake warms up so much more slowly, and cools off in the fall with corresponding slowness. The curves conform quite closely with the results given in my '97 paper, except that in the winter of '95 there was a large rise in March. This difference is accounted for by the fact that in the '95 collections a distinction was made between the Epischura larvae and the other copepod larvae. The annual occurrence of Epischura in Lake Winnebago re- sembles very closely the results given by Birge for lake Men- dot a. , The. nearest European relative of Epischura,, Heterocope, is stated by Apstein to occur from July to November, with a max- imum in the summer, thus showing a resemblance in its period- icity to Epischura. 26 PLANKTON OF WINNEBAGO AND GREEN LAKES. Limnocalanus macrurus Sars. Limnocalanus only occurs in deep lakes, so it is not found at all in Lake Winnebago. In Green lake it is found at all times of the year. In my former paper (Marsh '97) I stated that its maxima were in May and November. The curves from the present series of observations (Plate VI) seem to confirm the former results, although the spring maximum occurs as early as April in some years, in others as late as June, and in the summer of 1900 the greatest number during the year was in July, although there had been a marked rise in April. Dur- ing the winter months most of the individuals are larval forms. It will be noticed that the maxima of Limnocalanus are not very widely different from the smaller numbers found at other times. This is doubtless due to the habits of this species, which, as I have shown before, prefers a low temperature of the water, and during the summer months is found to very little extent above the thermocline. In the winter it is found at all depths. While, for the sake of the lower temperature, it suc- ceeds in adapting itself to the stagnant conditions of the deeper waters of the summer, it does not flourish at that time as it does when, the temperature being favorable, it can find a home at any depth. Cyclops brevisplnosus Herrick. C. brevispinosus is found in both Green lake and Lake Win- nebago. The curves (Plates VII and VIII) show that it should be ranked as a summer form, although it may be found at all times of the year. In the three summers under observa- tion there was a marked increase the latter part of July or the first of August. In 1902, however, the greatest number of the year was found about the middle of September. In Green lake apparently there may be expected a great in- crease in the latter part of June or in July. In December, 1902, however, I took the largest collections of the whole pe- riod of two and a half years. These results correspond with the results reported for Green lake in my former paper (Marsh. '97). S 8 L\ \ \ CO 9 cp s S .2 8 W > 3 3 i s 5 K CO 8 (A W m os • • 02 c! 8 § "(0 CD 28 9O ;8 ? j r^ a H § 0) 0> I I 0) O *- 0) O O 00 0) 0) :. ANNUAL DISTRIBUTION OF THE ORGANISMS. 27 Birge reports for Lake Mendota that the largest collections were made in May. This does not correspond to the results of either Green lake or Lake Winnebago, although in one year there was a considerable rise in Lake Winnebago in May. In gen- eral it may be stated that C. brevispinosus is a perennial form, flourishing especially in the months from May to October. Cyclops pulchellus Koch. Cyclops pulchellus does not occur in Green lake. In Lake Winnebago it is found from early October to the last of June. As the curves show7 (Plate IX) it has no very pronounced maximum, but it is evident that it is present in the greatest numbers in May or June. This species is then, in Lake Winnebago, distinctly a winter species. DISTRIBUTION OF C. brevispinosus AND C. pulchellus IN WIS- CONSIN LAKES. While I have found C. pulchellus in Lake Winnebago only in the months from October to June, inclusive, it is the com- mon limnetic form in some other lakes. This is notably so in the Great lakes. In certain of the Wisconsin lakes, so far as my observations have gone, C. pulchellus is always present as the limnetic form as C. brevispinosus is in Lake Winnebago and Green lake. I have gone over very carefully the list of lakes, from which I have had collections, to determine, if possible, what is the factor which makes one lake a brevispinosus lake and another a pulchellus lake, but so far without entire success. The following lakes, so far as I know, always have C. pul- chellus: Lake Geneva, Elkhart, Chain o' Lakes, Cedar lake Washington county, Birch lake, Stone lake, Sand lake, Lake Michigamme, and Long lake Fond du Lac county. All other examined lakes have brevispinosus. All the lakes hav- ing pulchellus, with the exception of Sand lake, are of the deeper lakes, and Sand lake has a maximum depth of fif- teen meters, thus being one of the deeper lakes of this type. 28 PLANKTON OF WINNEBAGO AND GREEN LAKES. On the other hand all of the lakes having brevispinosus, with the exception of Green lake, are of the shallow lake type. In- asmuch as pidchellus is found in the colder waters of the Great lakes, it would be a natural inference to suppose that its pres- ence in Lake Winnebago in winter had immediate relation to the winter temperature of the water, and that it might be found during the summer in other lakes where the water retains a low temperature through the year. It seems impossible, however, to establish any such rule. Generally speaking it is true that in the shallower lakes brevispinosus is the common limnetic form, while in the deeper lakes, which have a marked thermo- cline in the summer we find C. pulchellus, but the exceptions are so startling as to destroy most of the effect of the generaliza- tion. Cyclops Leuckarti Sars. C. Leuckarti occurs in both Green lake and Lake Winnebago, but at somewhat different periods. In Lake Winnebago it is perennial, but the numbers in win- ter are very small. It is found in considerable numbers from April to the last of October. It is apparent from the curves of frequency (Plate X) that its maximum period is in July and August, although in one year there was a great increase in May. In Green lake, on the other hand, it appears to have a fall maximum, although the total numbers observed were so small as to make one careful about drawing any -exact inferences. The cause of the difference in the curves of the two lakes is difficult to state. If the maximum of Green lake occurred somewhat later than that in Lake Winnebago it might be thought that the difference was due to the fact that the deeper body of water is heated more slowly, but in the curve of 1900 the maximum in Green lake is late in the fall, so that this can not be considered the real reason. 86 0) d> o) o o £ g CD 0 0) ® °> I" •S 85 0) O T- '*" o) 6 T- 0) O O co o> ov h i S >. o t § IV 8 (0 (0 CD OO CD ~* 9 ? (D (0 28 8 fr' a o. i i CD 8 g ANNUAL DISTRIBUTION OF THE ORGANISMS. 29 Cyclops prasinus Fischer. C. prasinus occurs in Lake Winnebago only in very small numbers, so that a curve of annual occurrence would mean very- little. I have found it in every month of the year except in March, April, and May. The largest numbers I have found in September and October. In Green lake (Plate XI) it is a perennial form, but occurs in considerable numbers only from July to November, inclu- sive. In 1899 there were marked maxima the first of August and the first of October. In 1900 there was a similar increase in August, a few days later than the preceding year, and a fall maximum the first of November. In 1901 there was only one maximum and that occurred just after the middle of Septem- ber. C. prasinus then seems to be distinctly dependent upon the summer temperature for its period of greatest development. COPEPOD LARVAE. Under this head were counted, not only nauplii, but all forms of immature copepods which were not sufficiently advanced in structure to be specifically determined. Inasmuch as it is im- possible to determine the species of these larvae, it is difficult to explain the maxima of the curves (Plates XII and XIII) as due to the increase of particular copepods. It is only by comparing these curves with those of the various species that we can conjecture to what species a given maximum is due. In many cases these maxima are doubtless due to more than one species. A glance at the plates shows that the total numbers of larval forms in Green lake are considerably larger than in Lake Win- nebago as only once in the two years and a half under observa- tion did the number in Lake Winnebago much exceed that in Green lake. This is no more than would be expected from the fact that the copepods play a much more important part in the plankton of deep water lakes than they do where the water is shallower. In Lake Winnebago larval forms are found at all times of 30 PLANKTON OF WINNEBAGO AND GREEN LAKES. the year with two pronounced maxima, one in the spring and one in the summer or early fall. In the summer of 1899 the summer increase was distributed from July to December, with no great rise at any time. In the summer of 1901 there was a single maximum in the middle of July, while in 1902 this maximum did not come until the first of September. In the spring of 1900 there was, about the first of April, the largest number found at any time in the whole period under observa- tion. In the next year, 1902, the maximum came about the middle of June. It is extremely difficult to correlate these curves with those of the mature copepods. The summer increase is doubtless largly composed of Diaptomus oregonensis and Cyclops brevis- pinosus, with some specimens of Cyclops Leuckarti and Epis- chura. A comparison of the summer curves of these species shows a very close relation with the curves of larvae. The win- ter larvae are probably entirely of Cyclops pulchellus. The spring maximum is composed of the three species, Cyclops Leuckarti, Cyclops pulchellus, and Dwptomus oregonensis. In Green lake the curves resemble in general those of Lake Winnebago, with the exception of the marked increases in the winter months. In the three summers under observation there was a single maximum coming in the successive years in July, August, and September. I know of no reason why there should have been this difference. In the summer the larvae probably belong to all the species of copepods except D. sicilis, Limno- calanus, and Episcliura. The rises in the winter months are due largely to the two latter forms. I have found larval E pis- chum only in February and March. The increase in October and November is because of the coming in of Diaptomus sicilis. The rise in the curve in May and June is doubtless largely due to the increase in D. minutus, which later forms one of the chief elements in the plankton. Diaplianosoma brachyurum Liev. Diaphanosoma is distinctively dependent for its development upon the high temperature of the summer months. In Lake X uJ « z IB 3 £ £ < o fc A .S: « BULLETIN APR. 1 o' E &a a QC 2 i 2: 2 a: m s O - fl: 0) A oT M z -3 899- 19O 9OO-19O O 0) B 0) ^ V / / ^ | rC; 1 i«e a. g ri & ..- -- . .(-• ----- >^ s ^ & _O i « ji — __— - • — — ^*= ~- z _ • __ — • — • , — • — ES • -^^- _/ \ ^v. \ \ \ £ ^ >rS "cj: 5 s OS' •g to | 8 BQ C £ 8 00 § (C 1 a 5 0' ANNUAL DISTRIBUTION OF THE ORGANISMS. 3} Winnebago (Plate XIV) it appears as early as the middle of May and reaches its maximum in July or August, then rapidly diminishes, to disappear entirely the last of October. In Green lake it does not appear ordinarily until into July, and reaches its maximum in August or September. Here, too, it disappears the last of October. These results compare very closely with those reached by Birge for Lake Mendota and those noted by the European authors, Apetein, Fric and Vavra, Burkhardt, Steuer, and Seligo. It will be noted that the season for Diaphanosoma in Green lake is later than in Lake Winnebago, as we would expect, be- cause of the more rapid warming of the shallower body of water. The total number in Lake Winnebago, too, is greater, and the maximum much more sharply marked. Daphnia liyalina Leydig and D. retrocurva Forbes. Under this head I have placed all the common limnetic Daph- nias, without attempting a closer specific distinction. In Green lake I think the form is retrocurva, while in Lake Winnebago both hyalina and retrocurva are found. In Green lake Daphnm may be found at all times in the year but between January and the last of May only in occasional specimens. Its principal time of life is between the first of June and the last of December. The results of the three summers given in Plate XY, compared with the curves of my former paper (Marsh '97), do not give sufficiently uniform results to in- dicate maxima occurring' with any great regularity. In the sum- mer of 1899 there were two distinct maxima, one the middle of July and one about the middle of October. In 1900 the two maxima were the last of August and the first of November, while in 1901 there were three maxima, all less pronounced than in the preceding years, one in July, one the latter part of August, and one the first of November. The curves would seem to indicate the common occurrence of two pronounced maxima, one in July or August, and one in October or Novem- 32 PLANKTON OF WINNE3AGO AND GREEN LAKES. ber. The curves of my '97 paper indicate the same general principle. In Lake Winnebago (Plate XVI) the maxima during the summer months bear a fairly close resemblance to those of Green lake, but there is, in addition, a pronounced maximum in May or early June. This spring maximum may be due to the increase of hyalina, as Birge's results would indicate the ex- istence of a spring maximum for this species. A comparison of the work of Birge on Lake Mendota and the published results of the European authors Zacharias, Apstein, Burckhardt, Seligo, and Steuer shows ^hat the occurrence of limnetic Daplinia is very similar the world over, the winter months having the minimum of production, and the greatest numbers appearing in the summer and fall. The absence of the spring maximum in Green lake is doubtless due to the slow warming of the deep body of water. Daphnia pulex var. pulicaria Forbes. This species I have not found at all in Green lake. In Lake Winnebago it appeared May 11, 1900, and was found in large numbers in June and then entirely disappeared. In 1901 I found it in a single collection, — that of June 8. When it occurred it was in the bottom waters, and was very noticeable because of its size. It is possible that scattering in- dividuals at other times were counted as Tiyalina, but if it oc- curred at all it must have been in very small numibers. Birge (Birge '97) has discussed in detail the occurrence of this species in Lake Mendota, stating that it occurs there in num- bers only in the odd numbered years. This does not seem to be true in Lake Winnebago. He also states that it is confined to the region of the thermocline, being limited above by the high temperature of the water and below by the impurity of the bottom waters. If this were true it would explain the dis- appearance of this species in Lake Winnebago in summer, be- cause this lake has no thermocline, and the whole body of water is heated to a high degree. It would seem that the conditions 5 Cft O 00 0) I 8 J[ ANNUAL DISTRIBUTION OF THE ORGANISMS. 33 in Green lake would be peculiarly favorable for Daphnia puLir carlo,, but I have never found it, although my collections have now covered a considerable number of years. In the other lakes examined in this investigation I found Daphnia pulicaria only in Shamrock and Pansy of the Clover Leaf lakes and in Pelican lake in two years. In the Clover Leaf lakes it occurred below the thermocline. Its occurrence in Pelican lake was somewhat unexpected, as this lake has no thermocline, and the species was found in August, after the lake was thoroughly warmed up. In former collecting trips I have found Daphnia pulicaria in the deep waters of Lake Beulah in July and August, and Pro- fessor Birge (Birge '97) has already noted that it is common in the deep waters of the Oconomowoc lakes, which probably should be classed with the small deep lakes. Bosmina. In Lake Winnebago I have not found Bosmina at all in the months of July and August. In 1899 it did not appear until the first of December, and very few were found in the winter months. There was a very large increase about the first of June. Then it abruptly disappeared and reappeared the last of September. There was a fall maximum the first of Novem- ber, and then a rapid decline. During the winter months there were very few, and no marked increase until the first of June, 1901, when there was an increase corresponding to that of the preceding year. It then disappeared and was found again the first of October, when it commenced to increase with great rapidity. In Green lake, as shown by the curves (Plate XVII) Bos- mina occurs at all times of the year. Comparing these curves with the curves in my former paper (Marsh '97) it would ap- pear that we may expect Bosmina to have a fall maximum in November or December. After this maximum there is a sharp decline and the number then grows gradually smaller until June or July, when generally there is a slow increase 3 34 PLANKTON OF WINNEBAOO AND GREEN LAKES. followed by a rapid rise in the fall, which may come as early as September, but more commonly occurs in October or Novem- ber. In 1900, by far the largest number of the year occurred in July. Nothing like this appeared in the other years, al- though there was an increase in July, 1899. I think it can be said safely that Bosmina has two annual maxima, one in the late spring or early summer, and one late in the fall. In comparing the two lakes under consideration we find that the spring maximum occurs earlier in Lake Win- nebago than in Green lake, probably due to the fact of the more rapid warming of the water in the shallow Lake Winnebago. In. some years the spring maximum fails to appear in Green lake. The fall maximum seems, on the whole, to appear in Green lake somewhat later than in Lake Winnebago. If this maximum is dependent on some conditions following the fall cooling of the water, this later appearance in Green lake is easily explained. But so little is known of the life history of Bosrmrui that one would hardly feel safe in hazarding an ex- planation. In comparing my results of the annual distribution of Bos- mina, there seems to be a good deal of discrepancy, but prob- ably the differences can be explained either by differences in local conditions or by the fact that most of the statements have been based on observations carried on for only a comparatively short, time. No other observations, so far as I know, have been published in America, and the statements of European authors would indicate that in some cases there were two distinct max- ima, but not in others. Eurycercus lamellaius O. F. Miiller. Eurycercus lamellatus does not occur in the limnetic plank- ton of Green lake, but in Lake Winnebago (Plate XVIII) it was an important element of the summer plankton in 1899 and 1900. Curiously enough I found it in only one collection in 1901, — that of June 8. In the summer of 1899 it was found in great numbers about the middle of July, but had almost dis- g c. 8 CD 00 CO (0 (0 O O •-* O 3 I I ^ M 3 g r * * 6 ^ i g $ < p 0 0) 0> di 6 - ANNUAL DISTRIBUTION OF THE ORGANISMS. 35 appeared by the first of August. There was a rapid increase the last of August, another decrease and a rise again about September 20. It then decreased until the middle of Octo- l>er, and had entirely disappeared in December. In July and August it was perhaps the most noticeable element of the plank- ton, its greater specific gravity causing it to settle first in the centrifuging process. In 1900 it appeared as early as MarcL, but did not commence to increase until well into June, and reached a single maximum about the first of August, then der creased rapidly and disappeared about the first of October. In 1901 it is evident that some untoward circumstances must have prevented its development. In the collections made early in July, 1899, Eurycercus was much more abundant over the mud bottom well out in the lake than it was over the stony bottom nearer shore. Late in July the conditions were reversed, that is, Eurycercus was more nu- merous over the stony bottom nearer shore. An attempt was made to correlate this fact with the movements of fish, but not with entire success. It was found that while Eurycercus waa prevalent, it was an important article of food for the sheeps- lieads, and apparently there was some movement of the sheeps- heads corresponding to the change in position of the greatest numbers of Eurycercus, but the observations were not suffi- ciently numerous so that any final statement could be made. Chydorus sphaericus O. F. Miiller. Chydorus occurs only occasionally in Green lake. In the summer of 1899 none were found. Considerable numbers were found in October of 1900, and it continued in small numbers in the collections until January, but was found in none of the later collections. In Lake Winnebago (Plate XIX) it appears, to be a perennial form. In the summer of 1899 it had a sharp maximum early in August. It then declined rapidly and only few were found until July of 1900, when there was a sudden and great increase. A still greater increase occurred about the first of November. 36 PLANKTON OF WINNEBAOO AND GREEN LAKES. I have made no systematic collections from other lakes, but I have found Chydorus in great numbers in Stone, Sand, and Pelican lakes in September. I think we may say this, — that Chydorus is a perennial form, reaching its greatest numbers in the months from July to No- vember, with its maximum probably in October or November, but with sometimes a very marked increase also in July. Leptodora hyalina Lilljeborg. Plate XX shows the annual distribution of Leptodora in Lake Winnebago. It was entirely absent from both lakes from November until May. In Lake Winnebago it occurs as early as the beginning of May, but in Green lake it does not appear until into July. It disappears in Green lake, too, early in September. In both lakes its principal occurrence is in the months of July, August, and September. The occurrence in Lake Winnebago corresponds very closely with Birge's state- ment in regard to Lake Mendota, although he has found them there as late as December. The observations of Burckhardt, Steuer, and Seligo in Eu- rope in regard to this species show that the occurrence there is very nearly the same as in this country. Cypris. An undetermined species of ostracod was found in both Green lake and Lake Winnebago collections. In Green lake it was found in September and October of two years and in Feb- ruary and March of one year. In Lake Winnebago its range seems to have been from the first of April to the last of Septem- ber. It was very much more abundant in the summer of 1899 than in that of 1900. It was not at any time present in suf- ficient numbers to play any noticeable part in the total amount of plankton. The Bloom. The phenomenon of the "bloom" or the "working of the lakes," or the "breaking of the meres" as it is called in Great .(£> 00 8(0 • A (O e]>od larvae were prominent, but here again Asterionella wras perhaps the most important. The maximum of the first of August, 1900, was due to several entomostraca, as in the case of the preceding year. Daphnia was less abundant than in 1899 but formed perhaps the most important factor in the larger maximum of Sept. 1. In March again occurs a winter maximum, as in 1900, but the total is much less. This was caused, as the year before, mainly by the enormous increase in Asterionella, associated with great num- bers of Synedra pulchella and Synedm acus var. delicatissima. In the summer of 1901 there was a single maximum in the latter part of July in which, as in the former years, Diaptomus minutus played a very prominent part; at this time, too, Cera- tium and Dinobryon were very numerous. In the winter of 1902 there was again an increase as in the two preceding years caused in part by the numbers of Diapto- mus sicilis, but more by the enormous numbers of Asterionella and Synedra pulchella. COMPARISON OF AMOUNT OF PLANKTON IN DIFFERENT YEARS. It will be seen, by a glance at the curves, that the total amount of plankton varies quite widely in the years under considera- tion, and the question arises whether there may be plankton poor years and plankton rich years. Three summers would hardly give material to decide such a question, but it may be noticed that the summer production in 1901 was distinctly less in both lakes than in the preceding years. It is interesting to notice in this connection, the plankton collections made in a 42 PLANKTON OF WINNEBAGO AND GREEN LAKES. series of northern lakes about the middle of August in 1900 and 1901. In all the lakes the collections of 1901 were much smaller than in 1900. It would seem probable then that the summer of 1901 was a plankton poor summer. I do not know what reason can be assigned for this fact. It is a somewhat significant fact, however, that the curve of mean temperature for 1901 differs distinctly from the mean in that it rises sharply to a maximum in the middle of July and then declines rapidly, instead of continuing at practically the same height through most of August as is commonly the case. It is possible that the short duration of the extreme hot weather of summer may have had some effect in reducing the amount of plankton. COMPARISON OF PLANKTON IN GREEN LAKE AND LAKE WINNEBAGO. In comparing the curves of the two lakes, perhaps the most noticeable difference is the enormously greater summer produc- tion in Lake Winnebago. This is due to the very much greater production of plants in the shallower lake. Green lake varies from the mean much less during the year than does Lake Win- nebago. The winter production in Green, lake is absolutely considerably greater than in Lake Winnebago. This, as has been pointed out before is due both to the greater number of entomostraca, and to the enormous production of Asterionella in Green lake, accompanied sometimes by a corresponding in- crease in the species of Synedra. I can only conjecture as to the cause of the greater winter production in Green lake, but I think it is possibly connected with the fact that it is very late before it is frozen over. Lake Winnebago, because of its slight depth, is cooled off early in the fall and is covered with ice while Green lake is still open and exposed to aeration. The actual amount of water in Lake Winnebago is small as compared with its superficial dimensions, and its supply of oxygen must be much smaller than that of a body of deep water like Green lake: thus it seems to me that the conditions for animal life ANNUAL DISTRIBUTION OF THE ORGANISMS. 43 must be much less favorable in Lake Winnebago in winter than in Green lake. I have very little to offer in the way of proof of this suggestion ; it is significant, however, that the only other lake from which I have winter collections, — Cedar lake, Wash- ington Co., — has an amount of plankton intermediate Between Green lake and Lake Winnebago. Because of its smaller size Cedar lake must be earlier than Green lake in freezing over, and bcause of its greater depth, — nearly 100 feet, — the amount of water as compared with its area is much larger than in Lake Winnebago, and we might expect a larger production of plank- ton than in that lake. COMPARISON WITH THE PLANKTON OF OTHER LAKES. The other lakes connected with the Fox river, namely Lake Poygan, Lake Wineconne, and Lake Buttes des Morts, resemble Lake Winnebago very closely in the plankton, but the amount is not so great. Of the other lakes, Pelican and Shawano were particularly rich in plankton. Shawano, at the time of one set of collections, had more plankton than Lake Winnebago. Peli- can, in three of the four years in which examinations were made, was considerably richer than Lake Winnebago. Both Shawano and Pelican are shallow lakes and comparable with Lake Win- nebago in their genejal characteristics. Sand lake in 1899 had about the same amount of plankton as Pelican, but much less in the three succeeding years. Stone, Birch, Cedar, and the Waupaca lakes may, in a general way, be classed together, all having considerably less plankton than the shallower lakes. The Eagle River lakes are connected by wide thoroughfares so that they resemble each other very closely, but the larger ones seem to have the greater amount of plankton. The same thing is true of the Waupaca chain of lakes. In the case of the large collections which were made in all these lakes, it was the plants also that formed the prominent part of the plankton. In Table III have been listed the volumes of plankton as ol> 44 PLANKTON OF WINNEBAGO AND GREEN LAKES. tained in the various lakes of the state. In addition to what has just been said in comparing the results with those in Green lake and Lake Winnebago, something should be said of the lakes as compared with each other. The collections on the northern lakes were made in the course of four rapid trips in four suc- cessive years. The collections of 1899 were made in the latter part of September, and those of the succeeding years about the middle of August. The collections were practically synchro- nous in each year, and a comparison of the figures is interesting, although, as I have said in another part of this paper, one must be careful about drawing inferences from a small number of collections, and it is only averages upon which one can place much reliance. In the following table, in which I have listed the lakes of this circuit for the sake of comparison, I have placed first Birch and Stone lakes which belong distinctly to the class of small deep lakes, next Sand lake, which is intermediate between the two classes, then the Clover Leaf lakes, which, although shal- low, yet because of their small size, have a marked thermocline; the rest of the list belong distinctly to the shallow lake type. As the Eagle River lakes do not differ materially in the amount of their plankton, I have listed only one, the largest, — Eagle lake. 1899. 1900. 1901. 1902. Birch 80.97 114.24 79.25 59.50 Stone 71.4 171.36 52.36 54.55 Sand 205.16 152.32 63.43 124.95 Clover Leaf: 90 44 59.50 71.4 114.24 33 80 92.11 107.10 35.70 232.05 Bass 53 55 Silver 63 78 Summit . 107 10 Tinner 214.2 Eagle 233 24 185.64 345.10 122.09 466.48 376.04 517.65 Shawano . . .... 114.24 107.10 ANNUAL DISTRIBUTION OF THE ORGANISMS. 45 When one examines this table, the degree of uniformity in successive years is somwhat surprising, for we must expect an- nual variations in the maxima of the total plankton. I have already called attention to the fact that all the collections of 1900 were larger than those of 1902. This was especially marked in the case of Birch, Stone, and Sand lakes, and was largely due in each case to the greater number of Crustacea, es- pecially of the Diaptomi; in Sand lake there was also a larger number of the algae in 1900, but it was in the Crustacea that there was the greatest difference. The large collection in Shamrock in 1902 was due in the main to the comparatively large number of Daphnia pulicaria; the great size of this form makes it, when present, an impor- tant factor in the total plankton. In the distinctively shallow lakes, Eagle, Pelican, and Shawano, the uniformity in the successive years was very marked, the differences being hardly greater than might be ex- pected from hauls made on successive days in the same year. It will be noticed that the uniformity in the case of the shallow lakes is much greater than in the deep lakes. In comparing the lakes with each other at each period of col- lection we find that Pelican has the greatest amount of plank- ton in the last three years, but was outranked by Sand lake in 1899. This large amount of plankton in Sand lake in 1899 was due to the abundance of "bloom," in which the most prominent plant was Anabaena. I think this is an exceptional record for Anabaena for, as I have stated before, the plants of the bloom flourish especially in warm weather, and we should not expect them late in September. The time of the collection, too, had been preceded by cold weather, and on the day of the- collection ice had formed by the roadside in the morning. Eagle lake was a constant second to Pelican in the years un- der examination. In regard to the other lakes there seems to be no fixed order of precedence. In comparing the years 1900 and 1901 it is interesting that 46 PLANKTON OF WINNEBAGO AND GREEN LAKES. the relative difference is much greater in the case of the deep lakes than is true of the shallow lakes. I have already remarked, in comparing the plankton of Green lake with that of Lake Winnebago, that Green lake has the greater amount of plankton in the winter, and I^ke Winnebago the greater amount in the summer. I think we may say that this general comparison holds in regard to all deep and shallow lakes. The deep lakes because of the later date of freezing, the larger amount of water, and hence the larger amount of available oxygen, will have a greater amount of winter plank- ton, while the shallower lakes will in summer have the greater amount of plankton because of the favorable conditions for plant growth produced by the higher temperature of the water and the relatively large area of the bottom that is reached by the sunlight. DISCUSSION OF RESULTS. 47 CHAPTER III. DISCUSSION OF RESULTS- VALUE OF PLANKTON COLLECTIONS. It is a little difficult to state just what value should be placed on the measurement of plankton collections in limnology. It is, of course, evident that such collections give material for the qualitative determination of the fauna and flora, so that lakes can be compared with each other with reference to the distribution of forms. Care must be taken in this, however, unless the lakes are under examination for a long period of time, for, while in general the annual appearance of any form will be at about the same time in all lakes, nevertheless this appear- ance is subject to considerable variation, partly from differences in local conditions, and partly from differences in other condi- tions of environment ; I think there is no doubt that the algae of the "bloom:" may differ in their maximum periods not only days, but perhaps weeks, when the lakes appear to have similar condi- tions. Thus it may happen that a form may be abundant in one lake, and absent or present in small numbers in another at any given time, but later or earlier it may be abundant in the second lake. The absence of a form at a particular time is not always proof that the form is never present. For example, Diaptomus sicilis might easily be overlooked in the fauna of Green lake if we were to depend entirely on summer collec- tions, or Cyclops pulcliellus in Lake Winnebago if no winter col- lectons were made. As has been indicated already, also, 48 PLANKTON OF WINNEBAGO AND UREEN LAKES. forms may be very abundant in one year and either entirely lacking or present in small numbers in another. So even for qualitative determinations, it is necessary, if one would be strictly accurate, to make collections not only at all seasons of the year, but for a series of years. When one makes plankton measurements, and compares one lake with another from such records, the results are valuable, but it must be recognized that they are subject to certain sources of error. It has been already indicated that the horizontal dis- tribution of the plankton is remarkably uniform. Yet this uni- formity is subject to wide variations, so that inferences from single plankton collections might be very erroneous. Safety in drawing conclusions lies only in averages, and the larger the number of collections from which those averages can be drawn the safer are the conclusions. It follows, I think, that refinements in plankton measurement are unprofitable. It must be acknowledged that the measure- ment by settling is inaccurate, and that the use of the centri- fuge, while more accurate, nevertheless still leaves a large margin of error. Of course measurement by weighing is exact, but the results hardly justify the labor necessary. I would not have it understood, from what has just been said, that I would throw discredit on plankton measurement, for this paper is evidence of the importance I attach to it, but I wish to emphasize the fact that such measurements never can have the merit of exactness, for allowance must always be mja.de for error. It is very desirable if lakes are to be compared with each other in regard to the amount of plankton, that they should be under continuous observation for a long time, preferably for a term of years, for there may be considerable differences in the plankton of successive years. DISCUSSION OF RESULTS. 49 RELATIVE IMPORTANCE OF PLANKTON CONSTITUENTS IN PRODUCING MAXIMA. In Lake Winnebago and shallow lakes of a similar type it ia evident that the great maxima are produced by plants. We have found in the discussion of the Lake Winnebago plankton that certain cladocera, like Eurycercus, sometimes form an im- portant part of the plankton, but it may be said generally that all large maxima are dependent for their size on plants. In deep lakes of the type of Green lake, the Crustacea, as com- pared with the plants, are much more abundant than in the shal- low lake, but even here, too, the plants, especially the diatoms, are to a considerable extent responsible for the maxima. This is shown very strikingly in the March maxima of Green lake. It will be noticed, too, that when Crustacea are largely imr portant in producing plankton maxima, it is not as a rule the result of the development of a single kind, but the result of the simultaneous development of several kinds. In the discussion of the total plankton of the lakes in the northern part of the state, I have stated that the August plank- ton of the shallowr lakes in successive years is more uniform than that of the deep lakes. This is explained, I think, by the greater relative importance of the Crustacea in the deep lakes, for there is greater variation in the maxima of the Crustacea than in those of the "bloom." In plankton collections cover- ing a period of years, we may expect the curves for the shallow lakes to show much greater uniformity than those of the deep lakes because of the greater importance of the vegetable part of the plankton. COMPARISON OF PLANKTON AND TEMPERATURE CURVES. The temperature curves of the lake waters are similar to the mean curves of the localities in which the lakes are situated, with of course fewer variations and with a summer maximum at a somewhat later period. The summer maximum of the sur- 50 PLANKTON OF WINNEBAGO AND UREEN LAKES. face in Green lake ordinarily comes in the early part or middle of August, while the annual mean of this part of the state has its maximum about the middle of July. Lake Winnebago, bo- cause of its slight depth, warms up more quickly and cools with corresponding quickness. In comparing the temperature curves with the total plankton curves we find only a general resemblance. The greatest amount of plankton, generally speaking, is found in the hottest months. K^membering what I have said before, that the plank- ton is largely dependent for its amount on the plants, this is what would be expected, inasmuch as a high temperature is fa- vorable to plant growth. In some cases a maximum seems to follow the period of highest temperature, but this, is by no means always the case. Inasmuch as plants are more impor- tant in the plankton of the shallow lakes, it follows that the plankton of such lakes follows the temperature curve more closely than does that of the deep lakes. The deep lakes have annual conditions more closely approaching uniformity, hence the variations during the year are less marked, and as they never reach the high summer temperature of the shallow lakes, they never have such a large production of plants like Gloio- irichia, Anabaena; and Lingbya. The fact, too>, that the Crustacea form so much greater pro- portion of the plankton in the deep lakes, makes the correspond- ence with the temperature curve less, for some of the Crustacea have winter maxima. In comparing the annual curves of the Crustacea, it appears that the summer maxima of most of them came somewhat earlier in 1899 than in 1900. This does not seem to be true of the general plankton. I have been interested to know what made the difference, but I am not sure that I have detected the real reason. The maxima of the general plankton, as has been said, are largely dependent on the plants rather than the ani- mals. It would seem then, that the cause which made the 1899 summer maxima of Crustacea greater than those of 1900 must liave been something that would affect Crustacea but would not DISCUSSION OF RESULTS. 51 affect plants. A comparison of the temperature curves of the two years shows that the summer maximum came somewhat earlier in 1899 than in 1900. This might explain the earlier maxima of the Crustacea, but I do not quite undestand why the plants should not have been equally affected. COMPARISON OF CURVES OF TOTAL PLANKTON" WITH CURVES OF PLANKTON CONSTITUENTS. As has already been noted, the curves of plant production follow very closely the curves of total plankton, for it is to plants that the great differences in the amount of plankton are due. There are some marked exceptions to this general rule, like the great maxima of certain of the diatoms. In general terms it may be said that the curves for animals also follow the total plankton curves, most of them reaching their maxima in the summer months. There are many excep- tions, however. Some of the Crustacea are perennial in their occurrence, and some have winter maxima. Somte of the roti- fera, too, occur only in the winter mjonths. Generally speak- ing, it is in the deep lakes that we find more of those animals having winter maxima, although there are some exceptions. Some of the Lake Winnebago rotifera, for instance, are found only in the winter season. It is evident, however, that the greater uniformity of conditions in the deep lakes would make winter production more possible. HORIZONTAL DISTRIBUTION. One of the questions to which especial attention was paid was the matter of the uniformity of horizontal distribution. I discussed this question in some detail in a former paper (Marsh J97, pp. 218-223) expressing my own belief that the numbers of Crustacea might vary widely in different parts of a lake, and that they might, at some times, be aggregated to- 52 PLANKTON OF WINNE3AGO AND QREEN LAKES. gether in swarms, but I did not attempt to explain the reason of the existence of swarms. I also stated my belief that single plankton collections might give erroneous impressions, and that an accurate measure of plankton could only be obtained by averaging a considerable number of collections. Reighard (Reighard ?98) acknowledges the uniformity of distribution of the individual constituents of the plankton. Yung (Yung '99 ), as the result of his studies on the plankton of Lake Leman, states positively that the horizontal distribution varies within wide limits and that there is no doubt of the ex- istence of aggregations of organisms in certain localities. The causes of these aggregations he states are diverse, but intimates that sometimes currents may accomplish this. Steuer (Steuer '01) states that in his opinion there is no further call for discussion, but that it must be admitted that under similar physical conditions the^o will be uniformity in horizontal distribution. He does not, nowever, give the reasons for this opinion. While I felt quite sure that my position on the question wasy in the main, correct, it seemed to me desirable to make a con- siderable number of collections to test the correctness of my statement in a somewhat conclusive way. Two questions presented themselves for solution. First, the comparative amounts of the plankton at different parts of the lake at any given time. Second, if it was proved that there was a difference in horizontal distribution, is this a fairly con- stant difference between any two localities, or is it one that may vary from day to day or from hour to hour ? To answer the first question, at several times collections were made at a considerable number of locations on the same day. The following table will show the results. In preparing this table, I have listed no collections where less than four locations were tested. In most cases the figures for the plankton were tiie average of three collections. Erratum: Page 52, line 6, for " uniformity" read " irregularity." DISCUSSION OF RESULTS. 53 Table showi.ig comparative amounts of plankton at different parta of the lakes at given times. Name of Lake. Date. Amount of Plank- ton. Coll. No. Lake Winnebago ........ 1899 July 10 142 8 99 22 Lake Winneba^o July 10 154 7 99 24 Xake Winnebago July 10 59.5 99 25 Lake Wiiipebacro July 10 101 15 99 27 July 10 83 3 99.28 Lake ^Vinneba^o July 11 41 65 99 SO Lake Winnebasro Ju!y 11 62 48 99 31 Lake Winnebago . July 11 59 5 99 32 L?ke Winnebt.o'o . ... July 11... 107 1 99 33 Lake Winnebago July 18.. . 130 9 99 62 Lake Winnebago July 18 107 1 99.65 Lake Winnebago July 18 172 55 99 66 Lake Winneba^o July 18 163 74 99. 65 Lake Winnebago July 18 139.94 99 67 July 18..- 72 83 99.68 July 18 119 99 69 Lake ^Tinnftbaoro July 22 215 85 99 87 Lake Winnebago July 2-2 206 11 99.fc8 Lake Winnebago July 22 ,333 2 99.89 Lake Winneba^o . July 22 130 9 99 90 Lake Winnebago July 22 141 70 99 91 Lake Winnebago July 22 126 85 J-9 92 Lake Winnebago July 27 201 85 99 118 July 27 226 1 99 122 July 27 194 45 99.124 Lake Winnebago July 27 261 8 99 . 125 Lake Winnebago July 27 224 2 99.126 Lake Winn°bago Aug. 4 130.9 99 160 Lake Winnebago Aug. 4 83.3 99.161 Lake Winnebago .... Aug. 4 124 95 99 162 Lake Winnebago . Aug. 4 91 15 99 163 Lake Winnebago Aug. 22 166 6 99 223 Lake Winnebago Aug. 22 151 7 99 22 i Lake Winoebago Aug 22 . .. 154 7 99 224 Lake Winnebago Aug. 22 154.7 99 226 Lake Winnebago Auff 22 130 9 99 228 Lake Winnebago Aug. 22 190.4 99 229 Lake Buttes des Morts .... Aug. 24 95 2 99 230 Lake Buttes des Morts Aug. 24 66 64 99 231 Lake Buttes des Morts Aug. 24 107.1 99 232 Lake Buttes des Morts Au». 24 130 9 99 233 Lake Buttes des Morts .... Aug 24 114 24 99 234 Lake Buttes des Morts Aug 24 59 5 99 235 Cedar lake, Washington Co. . . Aug. 4 124 95 99 154 Cedar lake, Washington Co. . . Aug. 4 119. 99.155 Cedar lake, Washington Co. . . Aug. 4 ... ... 130 9 99.155 Cedar lake, Washington Co. . . Aug. 4. ... ... 130.9 99.158 Cedar lake, Washington Co. . Aug. 4.. 130 9 99.159 54 PLANKTON OF WINNEBAGO AND GREEN LAKES. Table showing comparative amounts of plankton at different parts of the lakes at given times — continued. Name of Lake. Date. Amount of Plank- ton. Coll. No. Cedar lake, Washington Co. . . 1900 Mar. 24 57.6 0.16 Cedar lake, Washington Co . . Mar. 24 59.5 0.17 Cedar lake, Washington Co. . . Mar. 24 90.44 0.18 Cedar lake, Washington Co . . Mar. 24 83.3 0.19 Cedar lake, Washington Co. . . Mar. 24 71.4 0 20 Cedar lake Washington Co Mar 24 59 5 0 21 Cedar lake, Washington Co. . . Mar. 24 9.52 0.22 Lake Poygan 1899 July 23 111.15 99.93 Lake Poygan July 23 85.20 99.96 Lake Poygan July 23 87.35 99.97 Lake Poygan July 23 81.40 99.98 Lake Poygan July 23 107.1 99 99 Lako Poygan July 23 111.15 99 100 Lake Poygan Auar 6 123.76 99 166 Lake Poygan Auff 6 95.2 99.168 Aug. 6 23.8 99.169 Lake Poygfin Au^. 6 62.36 99 170 Lake Poygan Lake Poygan Aug. 6 Aue. 6 95.2 92 34 99.171 99.172 Aug. 6 53.55 99.173 Lake \Vinueconne Ausr 6 95.2 99 176 Lake Winneconne Aug 6 89 25 99.177 Lake Winneconne Aug 6 86 28 99.178 Lake Winneconne Aug. 6 81.33 99.179 Lake ^/inneoonne Au<* 6 107.1 99 180 Lake Winneconne Lake ^^inneoonn^ Aug. 6 July 24 110.08 101 15 99.181 99.109 Lake ^^inneconne July 24 130.9 99.110 Lake \Vinneconne July 24 117.10 99 111 Lake Winneconne July 24 114.24 99.112 Lake Winneconne July 24 i 112.57 99.113 Shawano lake Aug. 8 119. 99.186 Shawano lake Aug. 8 130.9 99.187 Shawano lake . ... Aug. 8 249 9 99.188 Shawano lake Aug. 3 220.15 99.189 DISCUSSION OF RESULTS. 55 The stations where these collections were made were chosen much at random, with the exception of those in Cedar lake, which were for the most part in the limnetic region. In many cases the stations of a given date were widely separated. In lakes Poygan and Winneconne they were scattered from one end of the lake to the other. In Lake Winnebago most of them were within two or three miles of the laboratory at Stony Beach. The route traversed on July 18, however, must have covered 16 or 18 miles. In looking over the table, the amount of uniformity is cer- tainly very striking. This is especially true of the collections in Cedar lake on Aug. 4, 1899, when five collections varied only from 119 to 130.9. These collections were all made in the lim- netic region, and the depths at the different stations did not vary greatly. The collections made in Cedar lake on March 24, 1900, were made through the ice, and the depth at the different stations varied from six meters to thirty-one meters. Collections 0.18, 0.19, and 0.20 were made at a depth of thirty-one meters, the depths at the other stations being as follows: 0.16 thirty meters, 0.17 twelve, and 0.22 six. There would seem in these collections to be a connection between the depth and the amount of plank- ton. This is perhaps, as would be expected, for the tempera- ture conditions in winter are practically uniform for all depths, and as temperature is one of the most important factors limit- ing distribution we might infer that increasing depth, under such conditions, would tend to increase the amount of plankton. Winter collections made on Green lake at other dates, not listed in the foregoing table, seem to confirm this generalization that during the winter months in a deep lake the amount of plankton varies, in a general way, with the depth. These facts in regard to the winter plankton led me to look over my notes to see whether there was evidence of any similar difference in the summer. My only available collections for this purpose were those made on Green lake, for the collections from Lake Winnebago were nearly all taken from what was 56 PLANKTON OF WINNEBAGO AND GREEN LAKES. practically a uniform depth, and the collections from other lakes were not numerous enough to have much bearing on the question ; it is interesting to notice, however, that in collections made in Birch lake in September, 1899, and August, 1900, which were made at different depths, the amount of plankton varied with the depth. It appears from the Green lake collec- tions that there is a distinct relation between the depth and the plankton, the amount of plankton increasing with the depth, but this difference is much less marked in summer than in winter. I do not remember to have seen any statements by other authors of the effect of depth on plankton. It is known, of course, that there is a difference in amount between littoral and limnetic plankton, but I think it is without doubt true, that in the limnetic plankton, depth is a factor in distribution, the variation in accordance with depth being most clearly marked in the winter. It does not follow, of course, that the deeper lakes necessarily have the greater amount of plankton — this certainly is not true, but simply that depth, in any given lake, is a factor to be considered in horizontal distribution. In the collections from Lake Winneconne, the uniform- ity is very marked. In this case the collections were made at different locations over the lake, and may be considered as typical of the whole lake. This is true in this lake, however, that the conditions vary little in different parts of the lake, and we would expect greater uniformity. In Lake Poygan the conditions are much as in Lake Winne- conne, both lakes being expansions of the Fox river: it is shal- low, the depth varying but little, with low swampy shores. We should expect, of course, a somewhat different fauna and flora in the weeds alongshore from that existing in the limnetic re- gion. But in the limnetic region, where the collections were taken, the winds and the currents must produce all the changes in environment. While the plankton differed more in Poygan than in Winneconne, yet, if we throw out 99.169, the variation is not very great. This collection was made in a place BUT- DISCUSSION OF RESULTS. 57 rounded by weeds, and it was noted at the time of the collection that the water was remarkably clear, although in most parts of the lake it was quite opaque because of the presence of vegetable matter. In Shawano lake the variation was somewhat greater than in Winneconne and Pbygan. Shawano varies more in its depths, but otherwise the conditions are much as in other lakes. It was from the collections made on Lake Winnebago, how- ever, that I hoped for the most conclusive results. These were made in considerable numbers and at such widely separated lo- calities that it seemed to me it would be a fair test of the uni- formity of horizontal distribution. I have placed in the foregoing table the amounts of plankton obtained in Lake Winnebago on seven different days when col- lections were made at several locations. The amount of uni- formity is certainly very remarkable, and was, I must confess, somewhat disheartening to me, for I had a theory to maintain. The variation does not, in any case, exceed the limits which Hensen says are compatible with uniformity, as he defines the term. In former papers (Marsh '97, and Marsh '01), I have dis- cussed this subject in detail, but the results of these collections in Lake Winnebago and adjoining waters have led me to modify somewhat the opinions then expressed, although I think they were, in the main, correct. There seems to be no question that in Lake Winnebago the horizontal distribution of the plankton is practically uniform. How then can I explain the results of collections as given in my former paper (Marsh '97) ? In the former paper I was discussing only Crustacea, and came to the conclusion that some of them were at times present in aggregations which might be called swarms. These aggrega- tions have been noticed by other observers, as for example Birge (Birge '97, 371). I acknowledge now that I have, in the past, attached too much importance to Crustacea as an element in the plankton. As will be shown later, the controlling element in the amount of 58 PLANKTON OF WINNEBAGO AND GREEN LAKES. plankton is the vegetable material. This is especially true in shallow lakes in which the Crustacea form', relatively a much smaller part of the plankton than they do in the deep lakes. The conclusions which I reached in my former papers were very largely derived from work on Green lake, in which the crus- tacea are more abundant than in Lake Winnebago, not only rel- atively to the vegetable organisms, but absolutely. It would follow that aggregations of Crustacea would affect the total plankton much more in the deep lakes. In lakes like Lake Winnebago Crustacea seldom form a controlling part of the plankton except when large numbers of certain of the cladocera are present, and then the total may be appreciably affected. For instance, in the collections listed for July 10, '99, tihe larger totals were caused by the presence of Eurycercus which was present in unusual numbers, and the evidence from my col- lections seems to show that Eurycercus occurs in moving aggre- gations or swarms that perhaps move under the influence of slow currents. The collections from the deeper lakes, like Green, lake and Stone lake, show greater differences when taken on the same day at different localities than do the collections from shallow lakes. In these deeper lakes the Crustacea form! a larger pro- portion of the plankton. My conclusions then are as follows: 1. I must acknowledge that the uniformity of horizontal dis- tribution is greater than I had formerly supposed. 2. Variations in uniformity, when general conditions remain the same, are largely due to variations in the numbers of erus- tacea. 3. Inasmuch as Crustacea, in deep water lakes are not only more abundant relatively to the plants, but are absolutely more numerous, it follows that the horizontal distribution of the plankton in deep water lakes will be less uniform than in shal- low water lakes. Large variations in the horizontal distribution of the plankton in shallow lakes will only be noticed, under ordi- nary conditions, when, for some reason, there is a local aggro- DISCUSSION OF RESULTS. 59 gallon of some of the larger cladocera, such as Daphnia or Eurycercus. 4. In winter the horizontal distribution of plankton in deep water lakes will bear a more or less close relation to the depth. This is explained by the fact that temperature is one of the most important factors in the control of the distribution of the plankton, and in winter the uniform temperature of the whole depth of water makes possible a larger production of plankton in deep water than in shallow. COMPARISON OF PLANKTON COLLECTIONS OVER MUDDY AND STONY BOTTOMS. As intimated earlier in this paper, in the regular collections on Lake Winnebago, one series was made over the muddy bot- tom, well out in the lake, and another over the stony bottom nearer shore. The average of the collections made in the summer of 1899, when they were made daily through lihe months of July and August, seems to show that the collections over the muddy bottom were decidedly larger than those over the stony bottom. This difference may be explained by the different effect of the character of the bottom! on the plankton, or by the effect of the slight difference in depth. I have shown elsewhere that the depth has an influence on the amount of plankton, and it is entirely conceivable that in the averages of a large number of collections, a difference of a meter or so in depth may have had a marked effect on the amount. Inas- much as the greatest depth at which collections were taken was only about five meters, a difference of a meter would mean a difference of twenty per cent., which might have a decided in- fluence on the amount of plankton. I am., therefore, inclined to explain the difference between the muddy bottom and the stony bottom as; due rather to the difference in depth than to the dif- ference in the character of the bottom. PLANKTON OF WINNEBAGO AND GREEN LAKES. CHAPTER IV. DISTRIBUTION OF SPECIES. GEOGRAPHICAL DISTRIBUTION. The ease with which plankton forms can be carried from place to place makes it unlikely that any lake will have a pecu- liar fauna or flora. The agencies by which this distribution is brought about have been fully discussed in other papers. Except, then, as the physical conditions are distinctly differ- ent, we should expect uniformity rather than diversity. As has been intimated already, ther^ is a distinct difference be- tween the constituents of the plankton of the Great Lakes and of smaller bodies of water, and in the smaller bodies there is a marked difference between the deep lakes and the shallow lakes. I have already discussed the distribution of Cyclops brevispi- nosus and Cyclops pulchellus, the first, as a rule, being confined to the shallow lakes and the latter to the deep ones. Diaptomus oregonensis is common to all the shallow lakes. Diaptomus minuius is not found in Lake Winnebago and the lakes immediately connected with it ; it occurs in the deep lakes, but is not strictly confined to them, as it may be found in others, especially in those that are further north. Cedar lake, Washington county, is peculiar in being the only lake in the state in which I have found Diaptomus siciloides. This is common in the states to the south and west of us, and it seems probable that it may be found in other lakes in Wisf- consin. Pelican lake is, I believe, the only lake of any size, which does not have large numbers of Diaptomus. I made a large num- DISTRIBUTION OF SPECIE 8. Q$ her of collections at different times without finding- a single specimen of this genus, and I had concluded that it was en- tirely absent from the lake, but in 1900 I found two or three individuals. This absence of Diaptomus is one of the most pecu- liar facts in distribution which I have run across. Pelican lake is a large body of water, with a maximum depth of about twelve and a half meters and with a large amount of plankton. It is considered a fine fishing lake, and one would expect an abundance of the ordinary Crustacea of the plankton. In the collections on the northern lakes work was carried on in two distinct drainage areas and I was interested to see whether any difference in the faunae and florae of the two areas could be detected. As I expected, there was no difference ex- cept that due to the difference in depth and general physical conditions of particular lakes. Generally speaking, the result of these collections was to con- firm the statements made by other authors and myself that there is practical uniformity in the fauna and flora of lakes over wide extents of territory, except as differences in depth produce con- ditions of especial character. It is strange, however, that with this general uniformity there should be cases of isolation like- that of Diaptomus siciloides in Cedar lake or of failure of oc- currence like the lack of Diaptomus in Pelican lake. In the discussion of the means by which organisms are dis- tributed from lake to lake I am inclined to think that too much: importance has been attached to the work of water fowl. Whiler doubtless, it is a proven fact that water fowl carry organisms, seeds, and eggs, from lake to lake, I imagine this is a very minor factor in distribution. It is a fact that communicating- bodies of water are pretty certain to have the same fauna and flora. This is very noticeable in the lakes in Michigan which are connected with Lake Michigan, for their faunae are iden- tical with that of the larger lake. The same is true of Lake Winnebago and its connecting waters. When lakes are pretty distinctly separated from each other, there is likely to be a dif- ference in fauna and flora. In other words "isolation" plays- $2 PLANKTON OF WINNEBAGO AND GREEN LAKES. a large part in producing differences in lake faunae. The chance planting of certain forms may determine the character of the fauna for a long period. Everything in Green lake would seem to> favor the growth of Cyclops pulchellus as the limnetic form of Cyclops. That it does not exist there, it seems to me, must be simply because it has not been planted, and there is no way it can reach that lake except through the agency of water-fowl. Diaptomus siciloides in some way got a foothold in Cedar lake, and remains there because of its isolation and is not carried to other lakes, because there are not suitable connect- ing bodies of water. I have noted in a former paper (Marsh '95), that Diaptom/as Reigliardi was found only in a few lakes in the northern part of the southern peninsula of Michigan. If water-fowl readily carried entomostraca from one body of water to another, it would seem very strange that this species should not appear in the lakes in northern Wisconsin, instead of being confined to such a narrow habitat. It is noticeable, too, that Diaptomus Reiyhardi in Michigan is, for the most part, found in lakes closely connected with each other. It appears, then, that isolation caused by the physical con- figuration of the country will tend to produce distinct differ- ences in plankton constituents, in spite of the other causes which may be at work to distribute animals and plants. COMPARISON OF THE FAUNAE AND FLORAE OF DIFFERENT CLASSES OF LAKES. The preceding subject leads naturally to the question of the fauna! and floral distinctions between the different classes of lakes. The classification, as made in the earlier part of this paper, was based on physical distinctions which must affect the environment and produce characteristic differences in the animals and plants. As a matter of fact it was such differences which first led me to suggest the division of lakes into deep and shallow. DISTRIBUTION OF SPECIES. 63 In the discussion of the annual occurrence of the various or- ganisms, these differences have already been noticed in detail, but it may be well to present them in a summarized form. In the case of plants the distinction between the different classes of lakes is more quantitative than qualitative, for the lit- toral conditions of deep lakes are such as to permit a great variety of forms, although they do not allow any large multipli- cation of numbers. So that while the plant production in the shallow lakes is vastly more prominent than in the deep lakes, most of the species of the shallow lakes can be found in greater or less numbers in the deep lakes. Clathrocystis and allied forms, and Oscillarw, however, may be considered peculiar to shallow lakes. Gloiotrichia, too, is a shallow lake form, but not exclusively so, as it occasionally occurs in large numbers in a deep lake. Anabaena is the ordinary form of the "bloom" of the deep lakes but it is not peculiar to them, but is even more abundant in the shallow lakes. Of the protozoa, Ceratium is character- istic of the deep lakes. It occurs in shallow lakes, but in lim- ited numbers. I do not find that Dinobryon can be considered as characteristic of any class of lakes, although European, au- thors have made the distinction between Chroococcaceae and Dinobryon lakes. So far as our Wisconsin lakes are concerned, Dinobryon can not be said to be characteristic of any class of lakes. Of the rotifers, Notholca longispina, while found in both classes of lakes, is found characteristically in the deep lakes; there it is common and sometimes in great numbers. Conochilus, while not found in all shallow lakes, seems, never- theless, to be pretty well confined to this type. Of the other rotifers, it can hardly be said that they are characteristic! of either class of lakes. Of the Diaptomi, D. sicilis belongs distinctly to the large deep lakes although it may be found as a migrant in some of the Michigan lakes, connected with the Great Lakes. D. minutus belongs to the large deep lakes but not exclusively so, for in northern Wisconsin and northern Michigan it may be found in (54 PLANKTON OF WINNEBAOO AND GREEN LAKES. some of the shallow lakes. D. Aslilandi has never been found outside the Great Lakes, and certain bodies of water immedi- ately connected with them. D. oregonensis is typical of the shallow lakes, but occurs in some lakes that would naturally be classed with the deep lakes, like Lake Mendota. Episcliura lacuslris is not confined to any class of lakes, but is more common in the deep lakes. Limnocalcmus macrurus is found only in the large deep lakes. Of the lakes within the limits of Wisconsin, only Green lake and Lake Geneva seem to furnish the necessary environment of low temperature with a certain amount of circulation. I have already discussed the distribution of Cyclops brevi- spinosus and Cyclops pulchellus. Of the species of Cyclops^ C. pulchellus is, generally speaking, characteristic of the deep lakes. The other species are common to both classes of lakes. C. brevispinosus, C. pulchellus •, and C. prasinus are limnetic in habit, C. Leuckarti is common to both the limnetic and the lit- toral regions, while C. fuscus, C. albidus, and C. serrulatus are littoral species. Of the cladocera, Lepiodora, Daphma hyalina,, Bosmina, Diaplianosoma, and Chydorus are common to all classes of lakes, but Bosmina is much more numerous in the deep lakes, and Lepiodora and Diaphanosoma are found in greater num- bers in the larger lakes. Daphnia pulicaria is found for the most part in the small deep lakes, while Eurycercus, which oc- curs in such numbers in the plankton of Lake Winnebago, is never found in the limnetic collections of the deep lakes. Peculiar to the abyssal fauna of Green lake are Mysis and Pontoporeia which are also abundant in the abyssal fauna of the Great Lakes. To sum up, while most of the constituents of the plankton are common to all classes of lakes, some few species are confined strictly to one class of lakes, while some of the others may be- considered characteristic of one class, although found in small numbers in other classes. The following may be considered characteristic of the deep lakes: Ceratium, Notholca longi- DISTRIBUTION OF SPECIE8. 35 spina, Diaptomus sicilis, Cyclops pulchellus. Peculiar to the large deep lakes are Limnocalarws macrurus, Mysis, and P07fc- toporeia, all being forms favored by the deep water conditions of the lakes of this class. Diaptomus Aslilandi should be added to the forms found only in large deep lakes, although it is not common to all large deep lakes, but is peculiar to the Great Lakes. Daphnm pulicaria may, I think, be considered a distinctive form of the small lakes, although sometimes found in lakes that perhaps would not fall in this class. The following may be considered as distinctively shallow lake forms: Clatlirocystis, Oscillaria^ Diaptomus oregonensis, and, perhaps, Eurycercus. The cladocera are much more abun- dant both in numbers and in species in the shallow lakes than in the deep lakes, but the forms are not peculiar, as they are generally littoral forms which have become limnetic in the lakes where the littoral and limnetic environments are very similar. COMPARISON OF PLANKTON OF SUCCESSIVE YEAES. It is evident that the plankton varies greatly in one year aa compared with another, and that the variation has no immedi- ate connection, in many cases, with differences in annual tem- perature. I take it that the variations may be explained by the relations of the organisms to each other. It has been a favorite notion of many biologists, in which I have shared, that the balance of life in a lake undisturbed by man is maintained with a good degree of exactness; that the animal production is based, in amount, on the plant production, and that the number of predaceous animals is conditioned on the numbers of the animals that serve as their prey. It would follow, of course, that in a lake where there were great possi- bilities in the way of plant growth, there would be a correspond- ingly large number of animals. From this has arisen the com- mon inference that it is the shallow lakes, in which the amount of vegetation is greatest, that are the best for the production of QQ PLANKTON OF WINNEBAGO AND &REEN LAKES. fish. It has also been inferred, — I have made the statement myself, — that inasmuch as in a state of nature there must be brought about an equilibrium between plant and animal growth, it is possible that man in his work of fish planting may disturb this equilibrium so as to interfere with the highest productive- ness of a lake; for it seems apparent that if an equilibrium be- tween plants and animals is once established, the introduction of any considerable number of either plant-eating or predaceous animals would bring in an element that would disturb nature's balance. The result of my work on these lakes leads me to think that this idea is very far from correct. Of course, it is true that in the long run a balance will be reached, but there may be wide swings of the pendulum on either side of this con- dition of equilibrium. It is evident that the maxima, under similar conditions of light and temperature, are not reached at the same time in different years, nor is the annual rotation of forms the same in different years. Some animals, according to Birge, seem to have biennial periodicity, but others, in which this is certainly not the case, appear in great numbers in some years and not in others. There is great variability in the an- nual records of a lake. It is apparent that certain forms, un- der favorable conditions, — conditions which it is frequently im- possible to define, — seem to get, such a start in the competition of life that they are produced in great numbers in some years, while in others they may hardly appear. Some animals, if the expression may be used, seem at times to get a momentum which carries them on to great production. When one stops to think of it this is no more than would be expected. Just as weeds overrun a farm, so certain forms of aquatic vegetation may, overtop everything else in a given year's production. The con- dition of a lake cannot be compared with that of a forest un- touched by man, for in the forest the vegetation is largely per- ennial, while in the lake the vegetation disappears each year, and in the annual reappearance it is conceivable that some form, from some little changes in the environment, may get a start that will shut off other forms. Thus, in spite of the fact that DISTRIBUTION OF SPECIES. (Jf the conditions of water are more stable than those of the land, there will be, in some ways, greater variability in the annual productiveness of the water. The changes in the vegetation will have a greater or less influence in controlling the animals, but in some cases, the animals seem to grow almost independ- ently of the plants. Examples of this apparently erratic production are seen in the comparison of the Gloioirichia curves in Lake Winnebago in the summers of 1899 and 1900, and in animals in the Diap- iotnus curve of 1901 in Lake Winnebago as compared with thafc of the preceding years, or the Diaphanosoma curve of 1899 as compared with the succeeding years. It is apparent that the balance of life is maintained much more evenly in deep lakes than in those that are shallower. It is to be noticed, too, that in the shallow lakes there is al- ways an overproduction of plants in the summer as compared with the animals. This has been remarked by many other authors. The overproduction becomes so great at some times in mid-summer that the water through the decay of the plants may become actually poisonous to the fish. RELATIVE VALUE OF DEEP AND SHALLOW LAKES FOR THE PRO- DUCTION OF FISH. If lakes are to be ranked for fish production in accordance with their amount of plankton, the shallow lakes must be con- sidered vastly the most valuable. As has been stated before, this is generally considered to be the fact. It seems to me, how- ever, that this difference, if it exists, has been much overstated. Fish are dependent for their food, for the most part, on the animal part of the plankton, not on the plants. It is the ento- mostraca that furnish the basis of food for fishes. Now4, in Green lake the1 entomostraca are not only more numerous than in Lake Winnebago relatively to the plants, but are also abso- lutely more numerous. They are at least as numerous in the summer, and during the winter there is a considerable produc- (53 PLANKTON OF WINNEBAGO AND GREEN LAKES. tion when they have almost disappeared in Lake Winnebago. May it not be, then, that Green lake may have as much of that ptart of the plankton that is useful for food for fishes as Lake Winnebago? I have not facts, from my study of Wisconsin lakes, to prove this, but it seems to me to be at least a reasonable conjecture. It is a somewhat significant fact to me that Stone lake is considered one of the best fishing lakes in the northern part of this state, and it is one of the deeper lakes, being nearly eighty feet in depth. It is true that Green lake is not a par- ticularly good lake for fishing at the present time, but this is probably because it is, to a considerable extent, "fished out." There is doubtless a difference between large and small deep lakes in favor of the larger lake in productiveness. As I indi- cated in a former paper (Marsh, '97, p. 180), this may be ex- plained by the more complete stagnation in the abyssal waters of the small deep lake. In the larger lake, in which the winds have better play, the waters are piled up by the prevailing winds at one end of the lake and return, in part, at least, by bottom currents, thus aerating to some extent the abyssal re- gions. This may explain the productiveness of Stone lake, for it is a long, narrow body of water extending in a direction from north to south and frequently violently disturbed by southwest winds which prevail in this location. It is probable that its abyssal regions are much less stagnant than, for instance, those of the Chain o? Lakes which are still deeper, but smaller, and surrounded by elevations which cut off the wind. I do not think it probable that, under similarly favorable conditions, deep lakes are ever as productive as the shallower ones, but I think the difference between the two has been much exagger- ated. In a deep lake the littoral, limnetic, and abyssal regions are quite sharply distinguished. There is, of course, no distinct dividing line between the littoral and limnetic regions, and the organisms of one may be found in the other, and yet the differ- ence between the fauna of the central regions of a lake and its shore is very marked. In a very shallow lake there is no true DISTRIBUTION OF SPECIES. (59 abyssal fauna, and in a pool the distinction between the limnetic and littoral regions is lost. In Lake Winnebago, as I have indicated in a former paper (Marsh '99, p. 181), in spite of its great size there is an inter- mingling of littoral and limnetic forms. Cladocera like Eury- cercus which are ordinarily considered strictly littoral are com- mon in the limnetic regions, and, on the other hand, limnetic forms like Diaptomus and the limnetic species of Cyclops may be found in the littoral region. In this lack of distinction be- tween the limnetic and littoral forms, Lake Winnebago is like an enormously overgrown puddle. PLANKTON Of WINNEBAGO AND GREEN LAKES. • LIST OF PAPERS QUOTED. APSTEIN, '96. Das Susswasserplankton ; Methode und Resul- tat© der quantitativen Untersuchung. C. Apstein. Kiel und Leipzig. BIRGE.. '97. Plankton Studies on Lake Mendota, II. The Crustacea of the plankton, July, 1894-Deo., 1896. E. A. Birga Trans. Wis. Acad. Vol. XI, pp. 274-448. BURCKHARDT, '00. Quantitative Studien liber das Zooplank- ton des Vierwaldstattersees. G. Burckhardt. Mittheil. der Naturforschenden Gesellschaft Luzern. 3 Heft. FRIG UND VAVRA, '94. Untersuchungen iiber die Fauna der Gewasser Bohmens. Fric und Vavra. Achiv der natur- \vissenschaftlichen Landesdurchforschung von Bohmen. IX Band. Ero. 2. KOFOID, '97. On Some Important Sources of Error in the Plankton Method. C. A. Kofoid. Sci. K S., Vol. VI, pp. 829-832. MARSH, '95. On the Cyclopidae and Oalanidae of Lake St. Clair, Lake Michigan, and certain of the inland lakes of Michigan. O. D. Marsh. Bull. Mich. Fish Com. No. 5. MARSH, '97. The Limnetic Crustacea of Green Lake. C. D'. Marsh. Trans. Wis. Acad., Vol. XI, pp. 189-224. MARSH, '99. The Plankton of Fresh Water Lakes. C. D. Marsh. Trans. Wis. Acad., Vol. XIII, pp. 163-187. HEIGHARD, '98. Methods of Plankton Investigation in their Belation to Practical Problems. J. Reighard. Bull. U. S. Fish Com., Vol. XVII, pp. 169-175. SELIGO, U. SCHROEDER, '00. Untersuchungen in den Stuhmer Seen. Nebst einem Anhang; das Pflanzenplankton preussischer Seeen. A. Seligo u. B. Schroeder. Danzig. STEUR, '01. Die Elntomostrakenfauna der aalten Donau" bei Wien. Adolph Steur. Zoolog. Jahrb. XV Band, Heft. LIST OF PAPERS QUOTED. 71 VOIGT, '02. Einige Ergebnisse aus den Untersuchungen ost- holsteinischer Seen. Max Voigt. Forschungsber. aus der Biolog. Station zu Plan, pp. 47-61. WARD, '95. A New Method for the Quantitative Determina- tion of Plankton Hauls. H. B. Ward. Proc. Amer. Mic. Soc., Vol. XVT1, pp. 255-260. WHIPPLE, '94. Some Observations on the Growth of Diatoms in Surface Waters. G. C. Wnipple. Technology Quar- terly, Vol. VII, pp. 214-231. YUNG, '99. Des Variations Quantitatives du Plankton dans le Lac Leman. E. Yung. Arch. Sci. Phys. et Nat Geneve. T. VIII, p. ,344-364. APPENDIX. 73 APPENDIX. TABLE I. — Record of total volumes of plankton per square meter in Green lake. These statistics are of limnetic plankton, averages being made when more than one collection was made at a given date. Date. Vol. in Date. Vol. in Date. Vol. in ccm. ccm. ccm. 1899. 1900. 1901. July 16.... 38.67 July 2.... 181.36 Apr. 1.... 77.35 July 31.... Aug. 25.... 103.29 34.75 July 16.... Aug. 4.... 71.4 104.72 Apr. 20.... May 4.... 32.37 22.13 Sept. 18.... 35.7 Aug. 13.... 64.26 May 18.... 47.6 Oct. 11.... 65.45 Sept. 3.... 142.8 June 1 40.46 Oct. 19.... 57.6 Sept. 15.... 53.55 June 22 59.5 Oct. 31.... 43.55 Sept. 29.... 51.65 July 8.... 61.88 Nov. 27.... 71.4 Oct. 16.... 53.55 July 20.... 76.16 1900. Oct. 27.... 49.98 Aug. 3.... 45.22 Jan. 13.... 50.69 Nov. 10.... 47.6 Aug. 27.... 30.7 Jan. 20.... 65.45 Nov. 24.... 47.6 Sept. 18.... 43.32 Feb. 23.... 197.54 Dec. 21.... 35.7 Oct. 19.... 35.7 Mar. 22.... 197.54 1901. Nov. 9.... 30.94 Apr. 20..,. May 5.... 95.2 107.1 Jan. 14.... Jan. '26 19.01 33.8 Dec. 9.... 1902. 29.75 May 21.... 122.81 Feb. 9.... 53.55 Feb. 19.... 46.17 June 2.... 226.1 Feb. 23.... 54.74 Sept. 12.... 77.35 June 16 399.84 Mar. 9.... 73.78 Sept. 13.... 71.4 PLANKTON OF WINNEBAGO AND GREEN LAKES. TABLE II. — Record of total volumes of plankton per square meter in Lake Winnebago. Statistics prepared as for Green lake. Date. Vol. in Date. Vol. in Date. Vol. in ccm. ccm. ccm. 1899 1899 1900 July 5. 71.4 Aug. 11.... 124.95 Aug. 22 316.55 July 6. 71.4 Aug. 12.... 90.20 Sept. 8.... 523.6 July 7. 119. Aug. 14.... 147.32 Sept. 22.... 152.12 July 8. 111.15 Aug. 15.... 133.76 Oct. 6.... 99.01 July 10. 108.29 Aug. 16.... 116.38 Oct. 20.... 66.64 July 11. 67.69 Aug. 17.... 111.03 Nov. 6.... 40.46 July 12. 136.85 Aug. 19.... 120.19 Nov. 21.... 18.8 July 13. 86.28 Aug. 21.... 128.52 Dec. 5.... 6.43 July 14. 111.79 Aug. 22.... 158.51 1901 July 15. 116.86 Aug. 26.... 144.22 Jan. 5 8.92 July 17. 124.24 Aug. 28 83.30 Jan. 19.... 7.26 July 18. 136.61 Aug. 30.... 176. IS Feb. 2.... 11.30 July 19. 137.92 Aug. 31... 95.2 Feb. 16.... 9.52 July 20. 183.26 Sept. 16 368.9 Mar. 2.... 17.13 July 21. 268 70 Oct. 7.... 92.82 Mar. 16.... 8.33 July 22. 191.83 Oct. 21.... 162.55 Mar. 30.... 6.54 July 25. 138.04 Nov. 4.... 99.92 Apr. 13.... 8.57 July 26. 162.75 Nov. 25.... 59.98 Apr. 27.... 16.94 July 27. 220.39 1900 May 11.... 35.22 July 28. 210.63 Jan. 1.... 33 32 June 8 29.75 July 29. 232.53 Jan. 27.... 65.17 June 25.... 42.84 July 30. 193.26 Feb. 17.... 30. July 12.... 172.55 July 31. 239.19 Mar. 3.... 10 47 July 27... 233. Aug. 1. 173.5 Mar. 17.... 7.38 Aug. 24.... 99.72 A ug. 2 . 146.61 Mar. 27.... 20 94 Sept. 13.... 127.09 Aug. 3. Aug. 4. 194.92 107.58 Apr. 28.... May 11.. 46.65 78.30 Sept. 28.... Oct. 12.... 79.73 32.74 Aug. 5. 101.15 May 24.... 180.40 Nov. 2.... 83.3 Aug. 7. 138.75 June 9.... 202.3 Nov. 16.... 23.8 Aug. 8 . 138.75 June 25.... 128.5 1902 Aug. 9. 114.95 July 9.... 138.04 Aug. 16.... 204.68 Aug. 10. 170.41 July 28.... 145.11 Sept. 2 .... 123.76 APPENDIX. 75 TABLE III. — Record of total volumes of plankton per square meter in various Wisconsin lakes. Name of Lake. Date. Vol. in ccm. Bass .... Sept. 25,1899.. 53.55 80.97 114.24 79.25 59.50 21.42 85.68 128.52 129.47 70.21 10:4.72 49.98 90.44 59.50 71.4 114 24 33.80 92.11 107.10 35.70 232.05 233.24 185.64 345.10 197.54 140.42 404.6 290.36 119. 428.4 309.4 172.55 452.2 83.3 214.2 48.74 122 09 466.48 376.04 517.65 97.23 77.06 87.11 64.26 205.16 152.32 63.43 124.95 179.93 Riroh Sept 22,1899 Birch Aug 11,1900 . Birch Aug. 7,1901 ... Birch Aug. 15,1902 Sept. 23,1898 Buttos des Miorts Buttes des Morts Aug. 24,1899 Buttes des JN^orts May 30,1900 Cedar, Washington Cedar, Washington Cedar, Washington Cedar, Sheboygan c Clover Leaf lakes: Golden Rod county Aug. 4,1899 county Mar. 24,1900 county Jan. 29,1900 Oct. 15,1898 Aug 9, 1900 Golden Rod Aug 10, 1901 Golden Rod Aug 10,1902 Pansy Aug 9 1900 Pansy AUO-. 10,1901 Pansy Aug. 10,1902... Shamrock Au». 9,1900 Shamrock Aug. 10,1901 Shamrock Aug. 10,1902 Eagle River lakes: Eagle Aug. 14,1900 Aug. 12, 1901 Eagle Aug. 13,1902 Aug. 14,1900 Otter Otter Aug 12,1901 . . Link Au°- 13,1902 ... Duck Aug. 14,1900 Duck Aug. 12,1901 Duck Aug. 13,1902 Yellow Birch Aug. 14,1900 Aug. 12,1901 Yellow Birch Yellow Birch Aug. 13,1902 Elkhart Oct. 1,1898 Long, Forest county Michigamme, Mich. Pelican Aug. 10,1900 Nov. 27,1902 Sept 24, 1899 . . Aug. 14,1900 Pelican Aug. 12,1901 Pelican Povsran Aug. 12,1902 July 23,1899 Poygan Aug. 6,1899 Aug. 6,1899 Povsran May 30,1900 Sand Sept 23,1899 Sand Aug. 11,1900 Sand Aug. 11,1901 Sand Aug. 11,1902 Shawano . . Aug. 8,1899.. 76 PLANKTON OF WINNEBAGO AND GREEN LAKES. TABLE III. — Continued. Name of Lake. Date. Vol. in ccm. Shawano Aug. 9,1900.. 114.24 Shawano Aug 8,1901. 107 10 Silver, Forest county Sept 22,1899. . 63 78 Stone. Sept. 23,1899 71 4 Stone . Aug. 12,1900.. 171 36 Stone . Aug. 11,1901. ... 52.36 Stone . Aug. 12,1902. . . 54.55 Summit Sept. 25,1899.. 107.10 Waupaca lakes: Rainbow July 29,1899 111.15 ItfcCrossen July 29,1899 73.30 Round July 29,1899 107 . 10 Columbian July 30,1899 104. Beasley's July 30,1899 95.2 Winneconne July 24,1899 110.91 Winneconne Aug. 6,1899 94.6 Winneconne Aug. 24,1899 64.26 Winneconne May 30,1900 17.6 APPENDIX. 77 TABLE IV. — Numbers of Diaptomus minutus and Diaptomus sicilis per square meter in Green lake. Date. No. Date. No. Date. No. 1899. 1900. 1901. July 16.... 163,744 July 2.... 159,936 Mar. 9.... 66,640 Aug. 1.... 706,384 July 16.... 198,016 1 Apr. 1.... 121,856 Aug. 25 Sept. 18.... 134,470 205,156 Aug. 4 Aug. 18.... 634,032 289,408 Apr. 20.... May 4.... 32,368 57, 120 Oct. 4.... 280,840 Sept. 3.... 447,440 May 18.... 34,272 Oct. 19.... 241,808 Sept. 15.... 127,568 June 1 47,600 Oct. 31.... 25, 704 Sept. 29.... 198,016 June 22.... 177,072 Nov. 27.... 32,368 Oct 16.... 171,360 July 8.... 215, 152 1900. Oct. 27.... 102,816 July 20.... 293,216 Jan 13.'... 28,560 Nov. 10.... 43,792 Aug. 3.... 205,632 Jan. 20 10,472 Nov. 24.... 38,556 Aug. 27.... 60,928 Feb. 23.... 78,064 Dec. 21.... 87,584 Sept. 18.... 116,144 Mar. 22.... 228,480 1901. Oct. 19.... 95,200 Apr. 20.... May 5 34,272 146,608 Jan. 14.... Jan. 25.... 79, 968 55,216 Nov. 9.... Dec. 9.... 53,312 72,352 May 21.... 91,392 Feb. 9.. 106,624 1902. June 2.... 47,600 Feb. 23.... 137,088 Feb. 19.... 110,432 June 16 158,032 PLANKTON OF WINNEBAGO AND GREEN LAKES. TABLE V. — Numbers of Diaptomus wegonensis per square meterin Lake Winnebago. Date. No. Date. No. Date. No. 1899. 1900. 1901. July 5-11.. 12,138 Mar. 3. 238 ;Jan. 5 357 July 12-18.. 12, 852 Mar. 17. . 476 Feb. 12.... 595 July 19-25.. 44,030 Mar. 27. . 952 Feb. 16.... 357 Ju.26-Aug.l 54, 978 Apr. 28. . 7,616 Mar. 2.... 238 Aug. 2-8.. 33, 320 May 11. . 952 Mar 16.... 714 Aug. 9-15.. 21,420 May 24. . 16,184 April 13.... 5,712 Aug.16-22.. 21,896 June 9. 16,184 April 27.... 9,044 Aug.23-29.. 16,184 June 25. . 19,992 May 11.... 2,380 Aug. 30- July 9. . 18,564 June 8 48,552 Sept. 5.... 19, 992 July 28. . 20,944 June 25 952 Sept. 16... 37,128 Aug. 22. . 34,272 July 12... 21,896 Oct. 7.... 8,092 Sept. 8. . 19,516 July 27.... 11,186 Oct. 21.... 17,136 Sept. 22. . 15,232 Aug. 24.... 94, 486 Nov. 4.... 39,984 Oct. 6. . 5,712 Sept. 13.... 119,000 Nov. 25.... 9,758 Oct. 20. . 11,424 Sept. 28.... 7,616 1900. Nov. 6. . 21,182 Oct. 12.... 15,708 Jan. 1.... 714 Nov. 21. . 7,616 Nov. 2.... 44,006 Jan. 27 .... 952 Dec. 5. . 2,856 Nov. 16.... 32,368 Feb. 17.... 238 TABLE VI. — Numbers of Epischura lacustris per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1899 1900 July 5-11. 714 Aug. 16-22. 476 June 9.... 6,188 July 12-18. 13,566 Aug. 23-29. 1,428 June 25 238 July 19-25. 2,656 Aug. 30- July 9.... 5,950 July 26- Sept. 5 952 July 28.... 476 Aug. 1 31,178 Sept. 16 476 Aug. 22.... 238 Aug. 2- 8. 1,428 1900 Sept. 22.... 238 Aug. 9-15. 1,666 1 May 24.... 714 APPENDIX. 79 TABLE VII. — Numbers of Epischura lacustris per square meter in Green lake. Date. No. Date. No. Date. No. 1899 1900 1900 July 16.... 3,808 July 2.... 2,856 Nov. 10.... 3,808 Aug. 1.... 17,136 July 16.... 1,904 1901 Aug. 25.... 1,904 Aug. 4 22, 848 June 22.... 1,904 Sept. 18 .... 238 Aug. 18 ... 3,808 July 8.... 3,808 Oct. 4.... 13, 328 Sept. 3.... 13,328 Aug. 3 952 Oct. 19.... 3,332 Sept. 15 .... 1,904 Aug. 27.... 1,428 Oct. 31.... 3,808 Sept. 29 476 Oct. 19.... 8,468 Nov. 27.... 238 Oct. 27 .... 2,142 TABLE VIII. — Numbers of Limnoealanus macrurus per square meter in Green lake. Date. No. Date. No. Date. No. 1899 1900 1901 July 16.... 3,808 July 2.... 1,904 Apr. 20.. . 4,760 Aug. 1.... 24,752 July 16.... 47,600 May 4.. . 9,520 Aug. 25.... 952 Aug. 4.... 9,520 May 18.. . 3,808 Oct. 4 .... 7,616 Aug. 18.... 5,712 June 1.. . 7,616 Oct. 19.... 3,094 Sept. 3.... 17,136 June 22.. . 22,848 Oct. 31.... 238 Sept. 15.... 952 July 8.. . 714 Nov. 27.... 7,616 Sept. 29.... 1,904 July 20.. . 952 1900 Oct. 16.... 1,904 Aug. 3.. . 952 Jan. 13 238 Oct. 27.... 476 Aug. 27.. . 5,712 Feb. 23.... 952 Nov. 24.... 19,040 Sept. 18.. . 3,808 Mar. 22.... 7,616 1901 Oct. 19.. . 1,904 Apr. 20.... 36,176 Jan. 14.... 476 Nov. 9.. . 3,904 May 5.... 8,468 Jan. 25 5,712 Dec. 9.. . 238 May 21.... 15,232 Feb. 23.... 13,328 1902 June 2.... 1,428 Mar. 9.... 6,664 Feb. 19.... 7,616 June 16 9,520 Apr. 1.... 12,376 80 PLANKTON OF WINNEBAGO AND GREEN LAKES. TABLE IX. — Numbers of Cyclops brevispinosus per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1899 1900 July 5-11. 8,806 Sept. 16.. _ 7,140 Sept. 22.... 1,904 July 12-18. 13,090 Oct. 7.... 2,380 Nov. 6.... 1,904 July 19-25. 5,236 Oct. 21.... 476 1901 July 26- Nov. 4 — 952 Mar. 30.... 238 Aug. 1 13,328 1900 July 12.... 10,472 Aug. 2-8. 17,612 May 11.... 5,712 July 27.... 19,992 Aug. 9-15. 5,236 July 9.... 12,376 Aug. 24.... 15,232 Aug. 16-22. 5,750 July 28.... 20,944 Sept. 18.... 30,464 Aug. 23-29. 6,664 Aug. 22.... 1,904 Sept. 28.... 19,992 Aug. 30- Sept. 8.... 2,856 Oct. 12.... 3,808 Sept. 5 5,236 TABLE X. — Numbers of Cyclops pulchellus per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1900 1901 Nov. 4.... 5,712 May 24.... 8,568 Mar. 30... 238 Nov. 25.... 6,664 June 9.... 1,904 April 27... 3,808 1900 Oct. 20.... 5,712 June 8... 7,616 Jan. 27.... 7,616 Nov. 6.... 952 June 25... 3,808 Mar. 3.... 238 Nov. 21.... 1,428 Sept. 28... 3,880 Mar. 17.... 7,616 1901 Oct. 12... 952 April 28.... 3,808 Jan. 19.... 238 Nov. 2... 15,232 May 11 18,088 APPENDIX. 81 TABLE XI. —Numbers of Cyclops Leuckarti per square meter in Lake Winnebago. Date. No. Date. I No. Date. No. 1S99 July 5-11.. July 12-18.. July 19-25.. July 26- 4,998 16, 136 13,804 1898 Sept. 16.... Oct. 7.... Oct. 21.... Nov. 4 17,136 3,094 476 238 1900 July 28.... Aug. 122.... Sept. 8.... Sept. 22 18,088 10,472 9,996 7,616 Aug. 1 Aug. 1-8 . Aug. 9-15. Aug. 36-22. 16,660 17,136 17,612 11, 424 1900 Mar. 17.... May 11 May 24 952 25,704 2,856 Oct. 6.... Oct. 20.... 1901. July 12 1,904 2,856 952 Aug. 23-29. Aug. 30- Sept. 5 11,424 21,420 June 9 June 25 July 9.... 1,904 952 32,368 Aug. 24.... Sept. 13.... Sept. 28.... 12,614 19,040 1,904 TABLE XII. — Numbers of Cyclops prasinus per square meter in Green lake. Date. No. Date. No. Date. No. 1899 1900 1901 July 16 ... 28,560 July 16.... 22,848 Apr. 1. 13,328 Aug. 1.... 104,720 Aug. 4 112,336 Apr. 20. 5,712 Aug. 25.... 23,672 Aug. 18.... 60,928 May 4. 3,808 Sept. 18.... 55,216 Sept. 3.... 59,024 May 18. 3,808 Oct. 4 .... 112,336 Sept. 15.... 34,272 June 1 . 7,618 Oct. 19.... 62,832 Sept. 29.... 38,080 June 22. 9,520 Oct. 31.... 41,888 Oct. 16.... 65,212 July 8. 1,904 Nov. 27.... 19,040 Oct. 27 .... 85,680 July 20. 19,040 1900 Nov. 10.... 72,352 Aug. 3. 15,232 Jan. 20 1,428 Nov. 24.... 26,656 Aug. 27. 39,984 Feb. 23.... 15,232 Dec. 21.... 9,520 Sept. 18. 74,256 Mar. 22.... 22, 848 1901 Oct. 19. 30,464 May 5.... 19,040 Jan. 25 13,328 Nov. 9. 20,944 May 21.... 15,232 Feb. 9 .... 13,328 Dec. 9. 32,368 June 2 .... . 17,136 Feb. 23.... 15,232 1902 June 16 11,424 Mar. 9.... 9,520 Feb. 19.... 17,136 July 2 .... 1,904 1 PLANKTON OF WINNEBAGO AND Q-REEN LAKES. TAALE XIII. — Numbers of copepod larvae per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899! 1900 1901 July 5-11. 11, 186 Mar. 17 ... 40,222 Jan. 19.. . 1,904 July 12-18. 74,970 Mar. 27.... 45,696 Feb. 2.. t 952 Julv 19-25. 69,498 Apr. 28.... 367,472 Feb. 16.. . 1,904 July 26- May 11.... 297,976 Mar. 2.. . 952 Aug.l 8,568 May 24.... 115,906 Mar. 16.. . 1,190 Aug. 9-15. 50,93-4 June 9 12,376 Apr. 13.. . 17, 136 Aug. 16-22. 43,078 June 25 49,980 Apr. 27.. . 57, 120 Aug. 23-29. 34,510 July 9.... 31,416 May 11.. . 30, 464 Aug. 30- July 28.... 129, 472 June 8.. . 118,048 Sept. 5 51,408 Aug. 22.... 101,150 June 25.. . 15,232 Sept. 16.... 6,664 Sept. 8 .... 42,840 July 12.. . 5,712 Oct. 7.... 49,504 Sept. 22.... 25,704 July 27.. . 3,808 Nov. 4.... 32,368 Oct. 20.... 2,856 Aug. 24.. . 27,608 Nov. 25.... 48,552 Nov. 6.... 8,568 Sept. 13 ... 48,744 1900 Nov. 21.... 1,428 Sept. 28 ... 39,508 Jan. 1 12,376 Dec. 5.... 1,904 Oct. 12.. . 21,896 Jan. 27.... 13,804 1901 Nov. 2.. . 22,848 Feb. 17.... 18,088 Jan. 5 952 Nov. 16.. . 20,944 Mar. 3.... 21,896 TABLE XIV. — Numbers of copepod larvae per square meter in Green lake. Date. No. Date. No. Date. No. 1899 1900 1901 July 16.... July 2.... 1,904 April 1.... 11,424 Aug. 1.... 249,424 July 16.... 100, 912 April 20.... 5,712 Aug. 25.... 69,258 Aug. 4.... 172, 261 May 4 13,328 Sept. 18.... 73,304 Aug. 18 .... 310,352 May 18.... 62,832 Oct. 4 .... 28,560 Sept. 3.... 137, 088 June 1 319,872 Oct. 19.... 9,520 Sept. 15.... 67,544 June 22 32,368 Oct. 31.... 34, 176 Sept. 29.... 57, 120 July 8.... 84, 152 Nov. 27 ... 72,352 Oct. 16.... 1,904 July 20.... 118,048 1900 Oct. 27.... 36, 176 Aug. 3.... 144,704 Jan. 13 47,600 Nov. 10.... 36, 176 Aug. 27 180, 880 Jan. 20 28,560 Nov. 24.... 51,408 Sept. 18.... 317, 968 Feb. 23.... 20,944 Dec. 21.... 196,112 Oct. 19.... 28,560 Mar. 22.... 19,040 1901 Nov. 9.... 22,848 April 20.... 22,848 Jan. 14.... 45,696 Dec. 9 74,256 May 5 .... 1,904 Jan. 25 32,368 1902 May 21.... 59,024 Feb. 9.... 95,200 Feb. 19.... 38,080 June 2 .... 81,872 Feb. 23.... 51,408 June 16.... 142,800 Mar. 9.... 20,914 APPENDIX. 83 TABLE XV. — Numbers of Diaphanosoma brachyurum per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1899 1900 July 5-11.. 14,280 Sept. 16.... 1,428 Oct. 6.... 7,616 July 12-18.. 28,322 1900 1901 July 19-25.. 194,208 May 11. . 238 May 11.... 476 July 26- May 24. . 4,760 July 12.... 9,520 Aug. 1 116,620 June 9. . 238 July 27.... 12,376 Aug. 2- 8. 32,368 June 25. . 952 Aug. 24.... 22,848 Aug. 19-15. Aug. 16-22. 30,464 19,992 July 9. . July 28. . 1,428 12, 852 Sept 13.... Sept. 28 952 2,142 Aug. 23-29. 5,712 Aug. 22. . 39, 984 Oct. 12.... 714 Aug. 30- Sept. 8.... 17, 850 Nov. 2.... 3,808 Sept, 5 11,424 Sept. 22.... 4,284 1 TABLE XVI.— Numbers of Daphnia hyalina per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1900 1900 July 5-11. 16,660 Jan. 1 238 Nov. 21.... 4,284 July 12-18 30, 464 Jan. 27.... 2,142 Dec. 5.... 476 July 19-25. July 26- 38,060 Apr. 28.... May 11.... 952 18,088 1901 May 11.... 476 Aug. 1 105,196 May 24.... 100, 198 June 8 22,848 Aug. 2-8. 12,376 June 9.... 13,328 June 25 5,712 Aug. 9-]5. 42,840 June 25 14,280 July 12.... 17, 136 Aug. 16-22. 44,268 July 9 ... 952 July 27.... 8,568 Aug. 23-29. 40,936 July 28.... 6,664 Aug. 24.... 10,472 Aug. 30- Aug. 22.... 43,792 Sept. 12.... 2,856 Sept. 5 40,936 Sept. 8.... 51,646 Sept 28.... 4,998 Sept. 16.... 14,756 Sept 22 ... 16, 184 Oct. 12.... 1,904 Oct. 7.... • 476 Oct. 6.... 3,808 Nov. 2.... 14,518 Oct. 21.... 5,712 Oct. 20 .... 5,236 Nov. 16.... 4,284 Nov. 4.... 7,140 Nov. 6.... 36, 176 Nov. 25 4,284 PLANKTON OF WINNE3AGO AND GREEN LAKES. TABLE XVII. — Numbers of Daphnia hyalina per square meter in Green lake. Date. No. Date. No. Date. No. 1899 July 16.... Aug. 1.... Aug. 25.... Sept. 18.... Oct. 4.... Oct. 19.... Oct. 31.... Nov. 27 13,328 93,396 4,760 3,094 22,848 26,894 1,190 1,428 1900 July 36.... Aug. 4.... Aug. 18.... Sept. 3.... Sept. 15.... Sept. 29.... Oct. 16.... Oct. 27 6,664 19,010 15,232 59,024 3,808 20,914 15,232 17, 136 1901 June 22 July 8.... July 20.... Aug. 3.... Aug. 27.... Sept. 18.... Oct. 19.... Nov. 9 952 7,616 19,040 6,664 26,656 24, 752 3,808 13, 328 1900 Nov 10 39, 984 Dec. 9 238 June 16 July 2.... 476 1,904 Nov. 24.... 9,520 TABLE XVIII. — Numbers of Bosmina per square meter in Green lake. Date. No. Date. No. Date. No. 1899 1900 1901 July 16.... 53,312 June 2 9,520 Jan. 25 19, 040 Aug 1.... 3,808 June 16.... 7,616 Feb. 9.... 7,616 Aug. 25.... 2,380 July 2.... 635,936 Feb. 28.... 11,424 Sept. 18.... 23, 800 July 16.... 325,584 Mar. 9.... 3,808 Oct. 4.... 24, 752 Aug. 4.... 12,376 Apr. 1.... 3,808 Oct. 19.... 24,752 Aug. 18.... 5,712 May 4 .... 1,904 Oct. 31.... 38,080 Sept. 3 .... 1,904 June 22 5,712 Nov. 27.... 173,264 Sept. 15 .... 13,328 July 8.... 7,616 1900 Sept. 29 .... 5,712 July 20.... 3,808 Jan. 13.... 114, 240 Oct. 16.... 1,904 Aug. 3.... 9,520 Jan. 20.... 79,968 Oct. 27.... 5,712 Sept. 18.... 7,616 Feb. 23.... 74,256 Nov. 10.... 59,024 Oct. 19.... 3,808 Mar. 22.... 138,992 Nov. 24.... 20, 944 Nov. 9.... 118,048 Apr. 20.... 36, 176 Dec. 21.... 19,040 Dec. 9 165,648 May 5.... 9,520 1901 1902 May 21.... 4,760 Jan. 14.... 3,8C8 Feb. 19.... 30,940 APPENDIX. 85 TABLE XIX.— Numbers of Eurycercus lamellatus per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1899 ' 1900 July 5-11.. 23,086 Aug. 23-29. 39,270 June 9 238 July 12-18.. 66,402 Aug. 30- June 25 12,852 July 19-25.. 22, 134 Sept. 5 19,040 July 9.... 10,948 July 26- Sept. 16.... 40, 460 July 28.... 40,460 Aug. 1 8,568 Oct. 2L.... 4,046 Aug. 22.... 20,944 Aug. 2- 8. 952 Nov. 4.... 238 Sept. 8 .... 4,284 Aug. 9-15. 1,428 1900 1901 Aug. 16-22 3, 332 Apr. 28 238 June 8 238 TABLE XX. — Numbers of Chydorusper square meter in Lake Winne- bago. Date. No. Date No. Date. No. 1899 1900. 1900 July 5-11. 19, 516 Jan. 27... 238 Dec. 5.... 1,904 July 12-18. 9,520 Mar. 27.... 476 1901 July 19-25. 2,856 Apr. 28.... 2,856 Jan. 5 238 July 26- Aug. 1 16,184 May 24.... June 9 1,904 3,208 Apr. 27.... May 11.... 952 1,904 Aug. 2-8.. 11,900 July 9.... 952 June 8 .... 2,142 Aug. 9-15. 28, 560 July 28.... 118,048 July 12.... 4,760 Aug. 16-22. 1,904 Aug. 22.... 6,664 July 27.... 21,896 Aug. 23-29. 238 1 Sept. 8 14,280 Aug. 24.... 1,904 Sept. 16.... 952 Sept. 22.... 18,088 Sept. 28.... 476 Oct. 21.... 476 Oct. 6.... 7,616 Oct. 12.... 952 Nov. 4 .... 2,618 Oct. 20.... 34,272 Nov. 2.... 3,808 Nov. 25.... 4,522 Nov. 6.... 133,518 Nov. 16.... 2,856 1900 Nov. 21.... 10,472 Jan. 1 — 952 86 PLANKTON OF WINNEBAGO AND GREEN LAKES. TABLE XXI. — Numbers of Leptodora per square meter in Lake Winnebago. Date. No. Date. No. Date. No. 1899 1899 1900 July 5-11. 714 Aug. 30- Sept. 8 .... 357 July 12-18. 952 Sept. 5 714 Sept. 22.... 238 July 19-25. 1,901 Sept. 16.... 1,904 Oct. 20.... 238 July 26- 1900 1901 Aug. 1 1,666 May 21.... 238 May 11.... 714 Aug. 2- 8. 952 June 9 238 June 8 .... 476 Aug. 9-15. 238 June 25.... 714 July 12.... 1,428 Aug. 16-22. 238 July 28.... 238 Aug. 24.... 238 Aug. 22-29. 476 Aug. 22.... 476 TABLE XXII. — Numbers of Gypris per square meter in Lake Win nebago. Date. No. Date. No. Date. No. 1899 1899 1900 July 5-11. 1,428 Aug. 23-29. 11,186 June 25.... 476 July 12-18. 10, 510 | Aug. 30- July 9.... 16,184 July 19-25. 53,788 Sept. 5 9,520 Aug. 22.... 1,904 July 26- Sept. 16.... 17,612 1901 Aug. 1 714 1900 June 8 714 Aug. 2- 8. 5,712 May 11.... 952 June 25 9,520 Aug. 9-15. 15,232 May 24.... 7,6L6 July 12 ... 952 Aug. 16-22. 16,422 June 9 2,856 APPENDIX. 87 TABLE XXIII. — Maximum depths of Wisconsin lakes. NOTE — It has been found, by experience, that the popular ideas in regard to the depths of lakes are utterly unreliable. Consequently, although only a small number of the Wisconsin lakes have been accurately sounded, it seems best to append a table of those depths that are known, to serve as a matter of reference. In 1897 a reconnaissance of a considerable number of the Wisconsin lakes was made by the author as preliminary to the study of the lakes undertaken by the Natural His- tory Survey of Wisconsin. Although this was a hasty trip, considerable care was taken to determine the greatest depths of the lakes visited, and where subsequent detailed sur- veys were made, it appeared that the record of the preliminary trip was quite accurate. Under the auspices of the Survey detailed hydrographic surveys were afterwards made of the following lakes : Lake Geneva, the Oconomowoc lakes, Lake Beulah, Elkhart lake, the Waupaca lakes, Delavan lake, the Lauderdale lakes, Green lake, Lake Mendota, and Lake Monona. The figures given for these lakes, then, are authoritative. The figures given for the other lakes are the result of only a cursory examination, with the probability that the deepest parts of the lakes were examined, but with the possi- bility of some error. The depths are the result of a personal examination by the autho r and were not obtained by any hearsay evidence. Name. Township. Range. County. Depth. Bass lakes . . ... 33 N. . . X E.. Langlade Feet. 19.5 Beaver Beulah 8N 4N XVIII E.... XVIII E.... Waukesha Wai worth 47.6 55.5 Mill 51.5 Round 40. Upper . . 67. Birch. 36 N. XV E Forest 61 7 Booth 4 N XVII E Wai worth 25.4 Buttes des Morts Cedar 18&19N 16 N. XV & XVI E XXXI E . Winnebago Sheboveran 9.7 39 Cedar UN.. IXX E.. Washington.. . 104 7 Clover Leaf 26 N. . . . XV E Shawano . . . Golden Rod 37 4 Grass .... 48.7 Shamrock 35.7 Crooked Delavan D'Eneveu 7N... 2N 15 N XVIIE.. XVIE XVII E Waukesha Wai worth Fond du Lac 16. 36.7 52 Eagle River lakes .... 39 &40N X & XI E... Vilas & Oneida. Catfish 16 6 Duck 16 2 Eagle . . . 49.7 Otter 29.2 Yellow Birch 15.5 East Troy.... . . 4 N . XVIII E Wai worth . 16 5 Elkhart 16 N. ... XXI E Sheboygan 113 2 Fowler . Garvin Genesee, North 8N 8N 7 N. XVII E XVIII E XVII E Waukesha Waukesha ... W^aukesha 50. 36.1 36 4 Genesee, South 7 N XVII E Waukesha 47.6 88 PLANKTON OF WINNEBAGO AND GREEN LAKES. TABLE XXII. — Maximum depths of Wisconsin lakes — Continued. Name. Township. Range. County. Depth. IN.. XVI, XVI E Walworth Feet. 142. Green 15 & Id N XII & XII E Green Lake.... 237. 6N X & XI E... Dane 46 6 Lac LaBelle 8N XVII E Waukesha .... 46.6 Laud^rdalo 4 N XVI E Walworth Green 56.8 Middle 50. Mill 50. Little Green 15 N . XIII E . Green Lake . . . 26. Lonsr 14 N .... XIX E Fond du Lac. . 45.5 Long 34 N.... XV E.. Forest 16.2 M^edicine 38 N XI E Oneida 13 T^lendota 7 & 8 N IX E Dane 84 !Monona 7 N IX & X E Dane 74. Mouse 8 N XVIII E.. Waukesha 66.3 Nagawicka 7 N XVIII E.. Waukesha 94.5 Nashotah Upper 7 N XVII E Waukesha 51.2 Nashotah, Lower .... Nenialibin, Upper 7 N 7 N XVII E XVII E Waukesha Waukesha 46.2 62. Nemahbiii, Lower .... North 7 N 8 N XVII E ..... XVIII E . Waukesha Waukesha . . 35.4 73.6 Oconomowoc 7 N XVII E . . Waukesha 62 6 8 N XVII & Otis 7 N.. XVIII E.. XVII E Waukesha Waukesha . . . 94. 28.3 Pelican 35 N . X &XIE.. Oneida 40 6 Pewaukee 7 N XVIII & Pine 8 N.. XIXE.... XVIII E.... Waukesha Waukesha . . 45.3 90. Powers 1 N. XVIII & Poyaran . . 19 & 20 N XIXE.... XIII, XIV Walworth and Kenosha 32.5 Sand 35 & 36 N & XV E ... XIII E . Winnebago & Waushara . . . Forest 11.4 48.7 27 N.... XVI, X VII E Shawano 17.9 Silver 36 N .. XIV E Forest 19.5 Silver 7N XVI E Waukesha 44. Sprint* . . 15 N.... XIII E Green Lake . . . 42.2 Stone 35 & 36 N XIII E Forest 76.4 Summit 33 N X E Langlade . ... 16.2 Tomahawk 38 & 39 N VI & VII E Oneida & Vilas 45.5 Twin 1 N XIX E . Lake Mary 26. Vieux Desert 42 N XIX E Vilas 19.5 Waubesa 6 & 7 N X E... Dane 36.6 Waupaca 21 & 22 N XI E Bass 9. Beaslev . . 52. APPENDIX. TABLE XXII. — Maximum depths of Wisconsin lakes. — Continued. Name. Township. Range. Connty. Depth. Waupaca: Columbian Feet. 66 6 Dake 28 5 Long 77 7 70 Marl 60 46 6 Mud 32. Otter 40 Pope 40 6 .Rainbow ... 95 1 Round 66.7 Taylor 55 7 Winnebafyo 15 & 20 N XVII & Winneconne 19 & 20 N XVIII E.. XV E Winnebago and Pond du Lac Winnebago . . . 25.1 9 7 INDEX. Abyssal fauna, 5. Anabaena, annual distribution of, 15. Annual distribution of the organisms of the plankton, 11. Anuraeaaculeala, annual distribution of, 19. cochlearis, annual distribution of, 19, quadridentata, annual distribu- tion of, 20. Aphanizomenun, annual distribution of, 16. Apstein, 13, 18, 19, 21, 22, 24, 25, 32. A splanchna, annual distribution of, 21. Asterionella, annual distribution of, 11,14. Balance of life more easily maintained in deep lakes, 66. Birge, 9, 24, 25, 26, 32, 33, 57. Bloom, discussion of, 36. Bosmina, annual distribution of, 33. table of numbers per square me- ter in Green lake, 84. Burckhardt, 32, 36. Buttes des Morts, 2. Centrifuge, use of, 9. Ceratium hirundinella, annual distribu- tion of, 18. Characteristic species of deep and shallow lakes, 62. Chydorus, table of numbers per square meter in Lake Winnebago, 85. sphaericus annual distribution of, 35. Classes of lakes, comparison of faunae and florae , 62. Classification of lakes, 6. Clathrocystis, annual distribution of, 15. Cloxterium, annual distribution of, 14. Codonella, annual distribution of, 19. Collections, on Green lake, times of, 5, 7. on Lake Winnebago, loca- tions of, 4. method of making, 8. Conochilus volvox, annual distribution of, 22. Copepod larvae, annual distribution of, 29. Counting plankton, method used, 10. Crustacea, important in total plankton in « deep lakes, 49, 50. Cyclops brevispinosus, annual distribution of, 26. table of numbers per square meter in Lake Winne- bago, 80. and C. pulchel- lus, local distri- bution in Wiscon- sin lakes, 27. Leuckarti, 'annual distribution of, 28, table of numbers per square meter in Lake Winnebago, 81. prasinus, annual distribution of, 29. table of nnmbers per square meter in Green lake, 81. pulchellus, annual distribution of, 27. table of numbers per square meter in Lake Winnebago, 80. and C. brevispinosus, local distribution in Wisconsin, 27. Cyclotella, annual distribution of, 11, 14. Cypris, 36. table of numbers per square meter in Lake Winnebago, 86. Depth, a factor in horizontal distribution, 56. Depths of Wisconsin lakes, 87. Diaphanosoma brachyurum, annual dis- tribution of, 30. tab'e of numbers per square meter in Lake Winnebago, 83. 92 INDEX. Dinobryon, annual distribution of, 17. Daphnia hyalina, annual distribution of 81. table of numbers per square meter in Green lake, 84. table of numbers per square meter in Lake Winnebago, 83. jowZezvar. pulicaria, annual dis tribution of, 32. retrocitrva, annual distribution of, 31. Deep lakes, definition of, 6. Diaptomus, rare ia Pelican lake, 60. gracilis, annual distribution compared with D. oregon- ensis, 24. graciloides, annual distribu- tation compared with D. oregonensis, 24. minutus, annual distribution of, 22. minutus and D. sicilis, table of numbers per square meter in Green lake, 77. oregonensis, annual distribu- tion of, 23. table of numbers par square meter in Lake Winnebago, 78. Reighardi, distribution of, 62. sicilis, annual distribution of, 22. siciloides, in Cedar Lake, 60- 62. Diatoms, comparison of annual distribu- tion in Green lake and Lake Winnebago with results of other authors, 13. Distribution, annual of the organisms of of the plankton, 11. annual of species, 60. Elkhartlake, 6, 27. Epischura lacustris, annual distribution of, 25. table of numbers per square meter in Green lake, 79. table of numbers per square meter in Lake Winnebago, 78. Epittylis galea, annual distribution of,' 19. Eudorina, annual distribution of, 15. Eurycercus lamellatus, annual distribu- tion of, 34. table of numbers per square meter in Lake Winne" bago,85. Fauna of different classes of lakes, 62. Fish, relative value of deep and shallow lakes for the production of, 67. Flora of different classes of lakes, 62. Fragilaria, annual distribution of, 12, 14. Geographical distribution of species, 60. Qloiotrichia, annual distribution of, 16. Green lake, 6, 7. comparison with Lake Win- nebago, 5. description of, 5. plankton compared with that of Lake Winnebago, 4. Heterocope, annual distribution of, 25. Horizontal distribution, 51. conclusions in re- gard to, 58. depth a factor in, 56. table of collec- tions, 53. Isolation important in producing differ- ences in lake faunae, 61. Kofoid, 9. Laboratory on Lake Winnebago, 3. Lakes, classification of, 6. Lake Geneva, 6, 27. Lake Winnebago, 6. character of work on, 4. comparison with Green lake, 5. description of, 2. plankton compared with that of Green lake, 42, why chosen, 1. Lakes visited other than Green lake and Lake Winnebago, 7. Lakes of Wisconsin, maximum depths, 87. Large deep lakes, 6, arge deep lakes more productive than small deep lakes, 68. Larvae, copepod, annual distribution of, INDEX. 93 Larvae copepod, table of numbers per square meter in Green lake, o2. table of numbers per square meter in Lake Winnebago, 82. Leptodora, table of numbers per square meter in Lake Winnebago, 86. Leptodora hyalina, annual distribution of, 36. Limnocalanus macrurus, annual distribu- tion of, 26. table ot num- bers per sq. meter in Green lake, 79. Lingbya, annual distribution of, 16. Marsh, 6, 10, 14, 22, 23, 31, 33, 51, 57, 62, 68, 69. Maxima of plankton, constituents produc- ing, 39. Measurement of plankton, method used, [9. Melosira, annual distribution of, 12, 14. Mendota, annual distribution of C. brevi- spinosiis in, 26. annual distribution of Z>. ore- gonesis in, 24. Merismopedia, annual distribution of, 15. Methods of making collections, 8. Nassula, occurrence in Lake Winnebago, 13. Navicula, annual distribution of, 13. Net, collecting, form of, 9. Notholca foliacea, annual distribution of, 21. longispina, annual distribution of, 20. Object of .study, 8. Oscillaria, annual distribution of, 16. Pediastrum, annual distribution of, 15. Pelican lake, Diaptomus rare in, 60. Plankton, amount in different years, 41. ' collections, value of, 47. comparison of collections over muddy and stony bottoms, 59. comparison of successive years, 65. constituents producing maxi- ma, 39. Plankton, constituents, relative import- ance of, 49. curves, comparison with curves of constituents, 51. curves, comparison with temper- ature curves, 49. maxima^ produced largely by plants, 49. method of examining, 10. method of measuring, 9. of Green lake, compared with that of Lake Winuebago, 42. of other Wisconsin lakes com- pared with Green lake, and Lake Winnebago, 43. table of total volumes per aq. meter in Green lake, 73. table of total volumes per sq. meter in Lake Winnebago, 74. total annual distribution of, 38. total volumes per sq. meter in various Wisconsin lakes, 75. Pleurosigma, annual distribution of, 13. Polyarthra plrttypera, annual distribu- tion of, 20. Poygan lake, 2. Reighard, 9, 52. Seligo, 19, 21, 22, 24, 32, 36. Shallow lakes, definition of, 6. Small deep lakes, 6. Species, distribution of, 60. Sphaerella, annual distribution of, 17. Staurastrutn, annual distribution of, 15. Stephanodiscus, annual distribution of, 13, 14. Steuer, 24, 32, 35, 39, 52. Stone lake, 2 Stony Beach laboratory, 3. Surirella, annual distribution of, 13. Synchaeta peclinaia, annual distribution of, 21. Synedra ocus var. delicatissima, annual distribution of, 12, 14. pulchella, annual distribution of, 12. Synura, annual distribution of , 18. Temperature curves, comparison with plankton curves, 49. Thermocline, classification of lakes de- pendent upon, 6. relation of Daphnia puli- caria to, 32. Total plankton, annual distribution of, 38. INDEX. Triarlhra longiseta, annual distribution of, 20. Uroglaena, annual distribution of, 18. Voigt, 14, 19, 22. Ward, 9. Water fowl as distributors of species, 61. Waupaca^lakes, 2,r16, 27. Whipple, 13. Winneconne lake, 2. Yung, 52. Zacharias, 18, 32. PUBLICATIONS OF THE Wisconsin Geological and Natural pistory Survey. 1. BULLETINS. The publications of the Survey are issued as bulletins, which are num- bered consecutively. Each bulletin is independently paged and indexed, no attempt being made to group them in volumes. The bulletins are issued in three series, A. Scientific Series. — The bulletins so designated consist of original contributions to the geology and natural history of the state, which are of scientific interest rather than of economic importance. B. Economic Series. — This series includes those bulletins whose in- terest is chiefly practical and economic. C. Educational Series. — The bulletins of this series are primarily designed for use by teachers and in the schools. The following bulletins have been issued: Bulletin No. I. Economic Series No. 1. On the Forestry Conditions of Northern Wisconsin. Filibert Roth, Special Agent, United States Department of Agriculture. 1898. Pp. vi., 78; 1 map. Sent on receipt of lOc. Bulletin No. II. Scientific Series No. 1. On the Instincts and Habits of the Solitary Wasps. George W. Peck- ham and Elizabeth G. Peckham. 1898. Pp. iv., 241; 14 plates, of which 2 are colored; 2 figures in the text. Sold at the price of $1.50 in paper and $2.00 bound \Bulletin No. III. Scientific Series No. 2. A Contribution to the Geology of the Pre-Cambrian Igneous Rocks of the Fox River Valley, Wisconsin. Samuel Weidman, Ph. D., Assistant Geologist, Wisconsin Geological and Natural History Survey. 1898. Pp. iv., 63; 10 plates; 13 figures in the text. Out of print. Bulletin No. IV. Economic Series No. 2. On the Building and Ornamental Stones of Wisconsin. Ernest Robert- son Buckley, Ph. D., Assistant Geologist Wisconsin Geological and Natural History Survey. 1898 (issued in 1899). Pp. xxvi,, 544; 69 plates, of which 7 are colored, and 1 map; 4 figures in the text. Sent on receipt of 30c. Bulletin No. V. Educational Series No. 1. The Geography of the Region About Devil's Lake and the Dalles of the Wisconsin, with some notes on its surface geology. Rollin D. Salisbury, A. M., Professor of Geographic Geology, University of Chicago, and Wal- lace W. Atwood, B. S.. Assistant in Geology, University of Chicago. 1900. Pp. x., 151; 38 plates; 47 figures in the text. Sent on receipt of 30c. Bulletin No. VI. Economic Series No. 3. Second Edition. Preliminary Report on the Copper-Bearing Rocks of Douglas county, and parts of Washbnrn and Bayfield Counties, Wisconsin. Ulysses Sher- man Grant, Ph. D., Professor of Geology, Northwestern University. 1901. Pp. vi., 83; 13 plates. Sent on receipt of lOc. Bulletin No. VII. Economic Series No. 4. The Clays and Clay Industries of Wisconsin. Part I. Ernest Robert- son Buckley, Ph. D., Geologist, Wisconsin Geological and Natural History Survey. In charge of Economic Geology. 1901. Pp. xii., 304; 55 plates. Sent on receipt of 20c. Bulletin No. VIII. Educational Series No. 2. The Lakes of Southeastern Wisconsin. N. M. Fenneman, Ph. D., Pro- fessor of General and Geographic Geology, University of Wisconsin. 1902. Pp. xv., 178; 36 plates, 38 figures in the text. Sent (bound) on receipt of 50 cents. Bulletin No. IX. Economic Series No. 5. Preliminary Report on the Lead and Zinc Deposits of Southwestern Wis- consin. Ulysses Sherman Grant, Ph D., Professor of Geology, North- western University. 1903. Pp. viii, 103; 2 maps, 2 plates, 8 figures in the text. Sent on receipt of 10 cents. Bulletin No. X. Economic Series No. 6. Highway Construction in Wisconsin. Ernest Robertson Buckley, Ph. D., State Geologist of Missouri, formerly Geologist, Wisconsin Geological and Natural History Survey. 1903. Pp. xvi, 339; 106 plates, including 26 maps of cities. Sent on receipt of 30 cents. Bulletin No. XL Economic Series No. 7. Preliminary Report on the Soils and Agricultural Conditions of North Central Wisconsin. Samuel Weidman, Ph. D., Geologist, Wisconsin Geological and Natural History Survey. 1903. Pp. viii, 67; plates 10, including soil map. Sent, paper bound, without charge, cloth bound, on receipt of 20 cents. Bulletin No. XII. Scientific Series No. 3. The Plankton of Lake Winnebago and Green Lake. C. Dwight Marsh, A. M., Professor of Biology, Ripon College. 1903. Pp. vi, 94. 22 plates. Sent, paper bound, without charge; cloth bound, on receipt of 25 cents. IN PRESS. Bulletin No. XIII. Economic Series No. 8- The Baraboo Iron Bearing District. Samuel Weidman, Ph. D., Geolo- gist, Wisconsin Geological and Natural History Survey. 2. BIENNIAL REPORTS. The Survey has published three biennial reports, which relate to admin- istrative affairs only and contain no scientific matter. First Biennial Report of the Commissioners of the Geological and Nat- ural History Survey. 1899. Pp. 31. Second Biennial Report of the Commissioners of the Geological and Natural History Survey. 1901. Pp. 44. Third Biennial Report of the Commissioners of the Geological and Nat- ural History Survey. 1903. Pp. 35. £3. HYDROGRAPHIC MAPS. There have been prepared hydrographic maps of the principal lakes of southern and eastern Wisconsin. This work is in charge of L. S. Smith, Assistant Professor of Topographical Engineering, University of Wis- consin. The following maps are now ready: Size of Plate, Inches. No. 1. LakeGeneva 17.5x10.8 No. 2. ElkhartLake 15.5xJ3.1 No. 3. LakeBeulah 22.5x20.0 No. 4. Oconomowoc-Waukesha Lakes 29.8x19.1 No. 5. The Chain of Lakes, Waupaca 21.7x20.6 No. 6. Delavan and Lauderdale Lakes .... 22.5x16.8 No. 7. GreenLake 26.0x17.8 No. 8. LakeMendota 23.7x19.5 No. 9. BigCedarLake 18.0x13.5 No. 10. LakeMonona 17.6x17.3 Scale, Inches Contour In- per mile, terval, Feet. 2 10 5 10 6 10 2 10 6 10 4 10 6 2.9 4 In all of these maps the depth of the ' lakes is indicated by contour lines, and by tints in all except No. 1. They are sent on receipt of 15 cents each except Nos. 4 and 8, for which 20 cents are required. They may be had either mounted in a manilla cover, or unmounted. All correspondence relating to the s urvey should be addressed to E. A. BIRGE, Director, Madison, Wis. 14 DAY USE RETURN TO DESK FROM WHICH BORROWED EARTH SCIENCES LIBRARY This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. LD 21-40m-5,'65 (F4308slO)476 General Library University of California Berkeley