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Bereta synh sah eat te yarn fae ee ake lopment Paces cameteareet Seoaceceen x fo 2uayeantalert meng ect raterus iol tiieyoeecincs is Shanes bpapeite rin. “ies pin Roomate af eases = pete re Sit cloced gent beth ae vacputen siepere acedsheh eae gm ral Cred eght eo 48) Feiss Fel ree ie ces ee eae . > , . see seritacetett Senedak einen ta Sac oe eae a oe ie =e ae = = 32 farts at eye cme Am oe AS ea 1 BBR gh | CORNELL UNIVERSITY THE Hlower Petecinary Library FOUNDED BY ROSWELL P. FLOWER for the use of the N. Y. STATE VETERINARY COLLEGE 1897 | /@Q : Ce Date Due ae If APR pian S,1- Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924000952808 ADVANCE PAGES FROM THE LIFE OF INLAND WATERS An elementary text book of fresh-water biology for American students / LP) By : JAMES G. NEEDHAM Professor of Limnology in Cornell University and ° J. T. LLOYD | Instructor in Limnology in Cornell University Issued for the temporary tise of the class in General Limnology in XH Cornell University : |G 3 7 and published “by The Comstock Publishing | Company Ithaca, New York de CORNELL UNIVERSITY THE Hlower Urterinary Library FOUNDED BY ROSWELL P. FLOWER for the use of the N. Y. STATE VETERINARY COLLEGE 1897 THE LIFE OF INLAND WATERS SPRING SUMMER Conditions on the AUTUMN WINTER Renwick Marsh at Ithaca. THE LIFE OF INLAND WATERS | An elementary text book of fresh-water biology for American students By JAMES G. NEEDHAM Professor of Limnology in Cornell University and J. T. LLOYD Instructor in Limnology in Cornell University 1915 THE COMSTOCK PUBLISHING COMPANY ITHACA, NEW YORK COPYRIGHT, I915 THE comsTock ‘PUBLISHING CO. 76 7 PRESS OF W. F. HUMPHREY, GENEVA, N. Y. PREFACE | Ga THE following pages we have endeavored to present a brief and untechnical account of fresh-water life, its forms, its conditions, its fitnesses, its associations and its economic pos- sibilities. This is a vast subject. No one can have detailed first hand knowledge in any considerable part of it. Hence, even for the elementary treatment here given, we have borrowed freely the results of researches of others. We have selected out of the vast array of material that modern limnological studies have made available that which we deem most significant. Our interests in water life are manifold. They are in part economic interests, for the water furnishes us food. They are in part aesthetic interests, for aquatic creatures are wonderful to see, and graceful and often very beautiful. They are in part educational interests, for in the water live the more primitive forms of life, the ones that best reveal the course of organic evolu- tion. They are in part sanitary interests; interests in pure water to drink, and in control’ of water-borne diseases, and of the aquatic organisms that disseminate diseases. They are in part social interests, for clean shores are the chosen places for water sports and for public and private recreation. They are in part civic interests, for the cultivation of water products for human food tends to increase our sustenance, and to diversify our industries. Surely these things justify an earnest effort to make some knowledge of water life available to any one who may desire it. : The present text is mainly made up of the lectures of the senior author. The illustrations, where not otherwise credited, are mainly the work of the junior author. Yet we have worked jointly on every page of thie book. We are indebted for helpful suggestions regarding the text to Professor E. M. Chamot, Dr. A. H. Wright, Messrs. W. A. Clemens and Ludlow Griscom. Miss Olive Tuttle has given much help with the copied figures. 10 Preface Since 1906, when a course in general limnology was first estab- lished at Cornell University, we have been associated in develop- ing an outline of study for general students and a program of practical exercises. The text-book is presented herewith: the practical exercises are reserved for further trial by our own classes; they are still undergoing extensive annual revision. The limitations of space have been keenly felt in every chapter ; especially in the chapter on aquatic organisms. These are so numerous and so varied that we have had to limit our discussion of them to groups of considerable size. These we have illustrated in the main with photographs of those representatives most commonly met with in the course of our own work. Important groups are, in some cases, hardly more than mentioned; the stu- dent will have to go to the reference books cited for further infor- mation concerning them. The best single work to be consulted in this connection is the American Fresh-water Biology edited by Ward and Whipple and published by John Wiley and Sons. Limnology in America today is in its infancy. The value of its past achievements is just beginning to be appreciated. The benefits to come from a more intensive study of water life are just beginning to be disclosed. That there is widespread interest is already manifest in the large number of biological stations at which limnological work is being done. From these and other kindred laboratories much good will come; much new knowledge of water life, and better application of that knowledge of human welfare. James G. NEEDHAM. J. T. Liovp. CONTENTS CHAPTER I Introduction The study of water life p. 14. Epoch-making events: the invention of the microscope, p. 15. The publication of the Origin of Species, p.17. The discovery of Plancton, p. 18. Agencies for the promotion of the study of Limnology, p. 20. Biological field stations, p. 23. CHAPTER II The Nature of Aquatic Environment I. Properties and uses of water: transparency, etc., p. 26. Stratification, p. 31. The content of natural waters, p. 40. II. Water and land, p. 55. CHAPTER III Types of Aquatic Environment I. Lakes and Ponds: Lakes temporary phenomena, p. 60. The Great Lakes, p. 63. The Finger Lakes, p. 64. The lakes of the Yahara valley, p. 66. Floodplain lakes, p. 67. Solution lakes, p. 68. Depth and breadth, p. 71. High and low water, p. 74. II. Streams: Gradient of stream beds, p. 77. Ice in streams, p. 80. Silt, p. 84. Current, p. 85. High and low water, p. 87. III. Marshes, swamps and bogs: Cat-tail marshes, p. 91. Okefenokee Swamp, p. 93. Climbing bogs, p. 94. Muck and peat, p. 95. High and low water, p. 96. CHAPTER IV Aquatic Organisms I. Plants: The Algae, p. ror. Chlorophylless water plants, p. 139. The mossworts, p. 146. The fernworts, p. 149. The seed plants, p. 151. II. Animals. Protozoans, p. 159. The lower invertebrates, p. 163. Arthropods, p. 183. Insects, p. 000. Vertebrates, p. 000. 12 Contents CHAPTER V Adjustment to Conditions of Aquatic Life I. Individual Adjustment. To open water, p. 000. Flotation, p. 000. Swimming, p. 000. To shore life, p. 000. Readaptation, p. 000. II. Mutual Adjustment: of plants with animals, p. 000. of plants with plants, p. 000. of animals with animals, p. 000. CHAPTER VI Aquatic Societies I. Limnetic. II. Littoral. CHAPTER. VII Inland Water Culture BIBLIOGRAPHY. issn cisvines day wai dais Vepadislda tans tea awa aleey Pp. 000 TMGOR ee siscc sai ik yep guard dig Gerace vagdese diye ees Bees ee ree awe KS p. 000 CHAPTER I INTRODUCTION (HE home of primeval man was by the waterside. The springs quenched his thirst. The bays afforded his most dependable supply of animal food. Stream- haunting, furbearing animals furnished his clothing. The rivers were his highways. Water sports were a large part of his recreation; and the glorious beauty of mirroring surfaces and green flower- decked shores were the manna of his simple soul. The circumstances of modern life have largely removed mankind from the waterside, and common needs have found other sources of supply; but the 13 14 Introduction primeval instincts remain. And where the waters are clean, and shores unspoiled, thither we still go for rest, and refreshment. Where fishes leap and sweet water lilies glisten, where bull frogs boom and swarms of May-flies hover, there we find a life so different from that of our usual surroundings that its contemplation is full of interest. The school boy lies on the brink of a pool, watching the caddisworms haul their lumbering cases about on the bottom, and the planctologist plies his nets, recording each season the wax and wane of generations of aquatic organisms, and both are satisfied observers. The study of water life, which is today the special province of the science of limnology*, had its beginning in the remote unchronicled past. Limnology is a modern name; but many limnological phenomena were known of old. The congregating of fishes upon their spawning beds, the emergence of swarms of May-flies from the rivers, the cloudlike flight of midges over the marshes, and even the ‘‘water bloom’’ spreading as a filmy mantle of green over the still surface of the lake— such things could not escape the notice of the most casual observer. Two of the plagues of Egypt were limnological phenomena; the plague of frogs, and the plague of the rivers that were turned to blood. Such phenomena have always excited great wonder- ment. And, being little understood, they have given rise to most remarkable superstitions.t Little real *Limnos=shore, waterside, and logos=a treatise: hydrobiology. {The folk lore of all races abounds in strange interpretations of the simplest limnological phenomena; bloody water, magic shrouds (stranded ‘“‘blanket- alge’’), spirits dancing in waterfalls, the ‘‘will o’ the wisp” (spontaneous com- bustion of marsh gas), etc. Dr. Thistleton Dyer has summarized the folk lore concerning the last mentioned in Pop. Sci. Monthly 19:67, 1881. In Keightly’s Fairy Mythology, p. 491 will be found a reference to the water and wood maids called Rusalki. ‘They are of a beautiful form with long green hair: They swing and balance themselves on the branches of trees, bathe in lakes and rivers, play on the surface of the water, and wring their locks on the green mead at the water’s edge.’’ On fairies and carp rings see Theodore Gill in Smithsonian Miscellaneous Collections 48:203, 1905. Limnology 15 knowledge of many of them was possible so long as the most important things involved in them—often even the causative organisms—could not be seen. Progress awaited the discovery of the microscope. The microscope opened a new world of life to human eyes—‘‘the world of the infinitely small things.” It revealed new marvels of beauty everywhere. It dis- . Fic. 1. Waterbloom (Euglena) on the surface film of the Renwick lagoon at Ithaca. The clear streak is the wake of a boat just passed. covered myriads of living things where none had been suspected to exist, and it brought the elements of organic structure and the beginning processes of organic development first within the range of our vision. And this is not all. Much that might have been seen with the unaided eye was overlooked until the use of the microscope taught the need of closer looking. It would be hard to overestimate the stimu- lating effect of the invention of this precious instrument on all biological sciences. 16 Introduction With such crude instruments as the early micro- scopists could command they began to explore the world over again. They looked into the minute structure of everything—forms of crystals, structure of tissues, scales of insects, hairs and fibers, and, above all else, the micro-organisms of the water. These, living in a transparent medium, needed only to be lifted in a drop of water to be ready for observation. At once the early microscopists became most ardent explorers of the water. They found every ditch and stagnant pool teeming with forms, new and wonderful and strange. They often found each drop of water inhabited. They gained a new conception of the world’s fulness of life and one of the greatest of them Roesel von Rosenhof, expressed in the title of his book, ‘‘Insekten Belusti- gung’’* the pleasure they all felt in their work. It was the joy of pioneering. Little wonder that during a long period of exploration microscopy became an end in itself. Who that has used a microscope has not been fascinated on first acquaintance with the dainty ele- gance and beauty of the desmids, the exquisite sculptur- ing of diatom shells, the all-revealing transparency of the daphnias, etc., and who has not thereby gained a new appreciation of the ancient saying, Natura maxime miranda in minimis.t Among these pioneers there were great naturalists— Swammerdam and Leeuwenhoek in Holland, the latter, the maker of his own lenses; Malpighi and Redi in Italy; Reaumer and Trembly in France; the above mentioned, Roesel, a German, who was a painter of miniatures; and many others. These have left us faithful records of what they saw, in descriptions and figures that in many biological fields are of more than historical importance. These laid the foundations of *Belustigung = delight. tNature is most wonderful in little things. Important Events 17 our knowledge of water life. Chiefly as a result of their labor there emerged out of this ancient ‘‘natural philosophy” the segregated sciences of zoology and botany. Our modern conceptions of biology came later, being based on knowledge which only the per- fected microscope could reveal. A long period of pioneer exploration resulted in the discovery of new forms of aquatic life in amazing richness and variety. These had to be studied and classified, segregated into groups and monographed, and this great survey work occupied the talents of many gifted botanists and zoologists through two succeeding centuries—indeed it is not yet completed. But about two centuries after the construction of the first microscope, occurred an event of a very different kind, that was destined to exert a profound influence throughout the whole range of biology. This was the publication of Darwin's Origin of Species. This book furnished also a tool, but of another sort—a tool of the mind. It set forth a theory of evolution, and offered an explanation of a possible method by which evolution might come to pass, and backed the explanation with such abundant and convincing evidence that the theory could no longer be ignored or scoffed out of court. It had to be studied. The idea of evolution carried with it a new conception of the life of the world. If true it was vastly important. Where should the evidence for proof or refutation be found? Naturally, the simpler organisms, of possible ancestral character- istics, were sought out and studied, and these live in the water. Also the simpler developmental processes, with all they offer of evidence; and these are found in the water. Hence the study of water life, especially with regard to structure and development, received a mighty impetus from the publication of this epoch-making book. The half century that has since elapsed has been one of unparalleled activity in these fields. 18 Introduction Almost simultaneously with the appearance of Darwin’s great work, there occurred another event which did more perhaps than any other single thing to bring about the recognition of the limnological part of the field of biology as one worthy of a separate recogni- tion and aname. This was the discovery of plancton —that free-floating assemblage of organisms in great water masses, that is self-sustaining and self-maintaining and that is independent of the life of the land. Lilje- borg and Sars found it, by drawing fine nets through the waters of the Baltic. They found a whole fauna and flora, mostly microscopic—a well adjusted society of organisms, with its producing class of synthetic plant forms and its consuming class of animals; and among the animals, all the usual social groups, herbi- vores and carnivores, parasites and scavengers. Later, this assemblage of minute free-swimming organisms was named plancton.* After its discovery the seas could no longer be regarded as ‘‘barren wastes of waters’; for they had been found teeming with life. This discovery initiated a new line of biological explora- tion, the survey of the life of the seas. It was simple matter to draw a fine silk net through the open water and collect everything contained therein. There are no obstructions or hiding places, as there are every- where on land; and the fine opportunity for quantita- tive as well as qualitative determination of the life of water areas was quickly grasped. The many expedi- tions that have been sent out on the seas and lakes of the world have resulted in our having more accurate and detailed knowledge of the total life of certain of these waters than we have, or are likely to be able soon to acquire, of life on land. Prominent among the investigators of fresh water life in America during the nineteenth century were Louis *Planktos = drifting, free floating. Aquatic Life 19 Aggassiz, an inspiring teacher, and founder of the first of our biological field stations; Dr. Joseph Leidy, an excellent zoologist of Philadelphia, and Alfred C. Stokes of Connecticut, whose Aquatic Microscopy is still a use- ful handbook for beginners. Our knowledge of aquatic life has been long accumu- lating. ‘Those who have contributed have been of very diverse training and equipment and have employed very different methods. Fishermen and whalers; col- lectors and naturalists; zoologists and botanists, with specialists in many groups; water analysts and sani- tarians; navigators and surveyors; planktologists and bacteriologists, and biologists of many names and sorts and degrees; all have had a share. For the water has held something of interest for everyone. Fishing is one of the most ancient of human occupa- tions; and doubtless the beginning of this science was made by simple fisher-folk. Not all fishing is, or ever has been, the catching of fish. The observant fisherman has ever wished to know more of the ways of nature, and science takes its origin in the fulfillment of this desire. The largest and the smallest of organisms live in the water, and no one was ever equipped, or will ever be equipped to study any considerable part of them. Practical difficulties stand in the way. One may not catch whales and water-fleas with the same tackle, nor weigh them upon the same balance. Consider the dif- ference in equipment, methods, area covered and num- bers caught in a few typical kinds of aquatic collecting: (1). Whaling involves the codperative efforts of many men possessed of a specially equipped vessel. A single specimen is a good catch and leagues of ocean may have to be traversed in making it. (2). Fishing may be done by one person alone, equipped with a hook and line. An acre of water affords area enough and ten fishes may be called a good catch. 20 Introduction (3). Collecting the commoner invertebrates, such as water insects, crustaceans and snails involves ordinarily the use of a hand net. A square rod of water is suffi- cient area to ply it in; a satisfactory catch may be a hundred specimens. (4). For collecting entomostracans and the larger plancton organisms towing nets of fine silk bolting-cloth are commonly employed. Possibly a cubic meter of water is strained and a good catch of a thousand speci- mens may result. (5). The microplancton organisms that slip through the meshes of the finest nets are collected by means of centrifuge and filter. A liter of water is often an ample field for finding ten thousand specimens. (6). Last and least are the water bacteria, which are gathered by means of cultures. A single drop of water will often furnish a good seeding for a culture plate yielding hundreds of thousands of specimens. Thus the field of operation varies from a wide sea to a single drop of water and the weapons of chase from a harpoon gun to a sterilized needle. Such divergencies have from the beginning enforced specialization among limnological workers, and different methods of studying the problems of water life have grown up wide apart, and, often, unfortunately, without mutual recognition. The educational, the economic and the sanitary inter- ests of the people in the water have been too often dealt with as though they are wholly unrelated. The agencies that in America furnish aid and support to investigations in fresh water biology are in the main: 1. Universities which give courses of instruction in limnology and other biological subjects, and some of which maintain field stations or laboratories for investi- gation of water problems. 2. National, state and municipal boards and surveys, which more or less constantly maintain researches that bear directly upon Investigations 21 their own economic or sanitary problems. 3. Socie- ties, academies, institutes, museums, etc., which variously provide laboratory facilities or equip expedi- tions or publish the results of investigations. 4. Private individuals, who see the need of some special investigation and devote their means to furthering it. The Universities and private benefactors do most to care for the researches in fundamental science. Fish commissions and sanitary commissions support the applied science. Governmental and incorporated insti- tutions assist in various ways and divide the main work of publishing the results of investigations. It is pioneer limnological work that these various agencies are doing; as yet it is all new and uncorre- lated. It is all done at the instance of some newly discovered and pressing need. America has quickly passed from being a wilderness into a state of highly artificial culture. In its centers of population great changes of circumstances have come about and new needs have suddenly arisen. First was felt the failure of the food supply which natural waters furnished; and this lack led to the beginning of those limnological enterprises that are related to scientific fish culture. Next the supply of pure water for drinking failed in our great cities; knowledge of water-borne diseases came to the fore: knowledge of the agency of certain aquatic insects as carriers of dread diseases came in; and suddenly there began all those limnological enter- prises that are connected with sanitation. Lastly, the failure of clean pleasure grounds by the water-side, and of wholesome places of recreation for the whole people through the wastefulness of our past methods of exploitation, through stream and lake despoiling, has led to those broader limnological studies that have to do with the conservation of our natural resources. *(payipowr ‘plojoyy 1997e) sUOTYRIS Poly [eorsojorg UeolJeury Jo UOTyeOO] BuIMmOoYsS dey *% “OTT oO SL 09 380 06 e737 00r °SOl 00M" ostt a We —_ ~, rot 4 23 Biological Field Stations “eMOT jo Apsiaatug, ey} JO UOoT}eIG PPI “eaol ‘axe troqoxO “yet jo Aysiaatg oY} jo vole, “21S PPM “Ye3N ‘APT Jeayig ‘uOT}eYG [eoLsoforg JozeM -yselg UeIpeueD “olleyUC, puelpiypy wou ‘Avg ewoy O04) “worye1g [eorsoorg oypoeq = “eiquinjopD yshld ‘oumreueN Jeou ‘Aeg einqredoq “solseysty jo nesing ueIpeueD jo or -e}g Bulyeo,,y ‘oeqenO ‘edsey ‘uoTyeEYG yeorsojorg suey ‘yOIMsUnIg MON ‘sMoIpUuy 4S “BuIpedeid ay} Jo UOT}eDO] Joyseq ‘eruropiyeg ‘oserq] ues “eIUIOJ -YyeO jo AqisIeatuy ay} jo uoryeyG eorsojorg suUTIeyy ayL “erusoneg ‘eyof eT ‘odaT]OD BuOUIOg jo Asoyeioqey ouleyy eunsey ‘eruloyyegQ «6 ‘yoeeg = Bunse’] “eIUIOJI[ED UlOYy NOG jo AjIsIaATUY) BY} JO WOT}EIS jeogojorg) ~pue wimntzenby asoaA = “BTUIOFITEQ) §« ‘oTua A, “AjISIOATUL) ployueyg puvyje’yT jo Aloyeloqey] episeeg suny -doy] “eluiopieg ‘acorn oywoedg of, 67, "Bl % ‘Lt ‘92 Cz hz ez ‘tS ‘Ie ‘0% “europe jo Ayisiaatug ayy Jo AdojorsAyg jo queuredaq ey} jo At04 -elOqe] YoIeasoyY UWleyszIoy “erusoplyeg, ©‘AoIoyUOPE MON ‘WOT]eYS BUTIeJ\[ punos yosng ‘uoysulysepy ‘Ioqrezy, Aepiiy ‘Aroyesioqe’y ureyunoyyy Opelojog ‘oper1ojod ‘puryTjoL ‘UOT}EYS [ROISOJOIg BURUOT[ ‘eueyuop, «aye = peayyeyy “u0Ty ~B4S Teorsojorg e}OHeC] YIION ‘eqoyeqd YWON ‘eye sytaeqd ‘AvAing AioysIy [enyeN ayeqg ‘UIsUODSTAA Jo AqISIOA -luQ) 944 Jo AztOyeIOqeyT [eo -1Z0]00Z “UISUOOSIM ‘UOSIPe]T ‘raaTy tddis -SISSTJAT 9t]} UO SeTIOYsTy TEYs -[eag JO uorlyesysoauy oY} roy AloyeIOgey] solleysty jo neeing ‘S$ ‘Q ‘eMoy “Jodineg * £10} “SIT TeinyenNy jo Aroqesoqe’y aye}g SIOUNj[ ay} JO yom JOAII ay} JO sioyrenbpeoy Suljecjy ‘siouly ‘eueaey uBsIYOT|[ Jo AjisioAluy) ayy JO UOT}LIG [BoLsojOIg JOU -UING ‘WesTyoTy ‘ayxe’] sepsnog ‘61 eI wT. OTs “OTe ‘VI, Cry Iz "II, “AYISIOATU aye4S O1YO ay} Jo A1ozeIOgGe’T ayey oy “oro ‘Aysnpurg (aye’y AoyING, uo AjJeutiog) ApIsioaluy, vue “IpU] JO UOLIeIS Pfr [eorso] -Olg ‘“BURIPUl ‘oYe] BUOUTM uot} -nUIysuy o1soured oy} jo Aso -Jolg ouLrepy Jo Juemyredeq ayy jo wuoryeyg yeorsoforg suey, «= epwo,y =‘sesnqzoy, “yoreasay [eo -IZ0]OTg JO} UoT}e}g epNueg ‘spuels[ epnuneg ‘uoyTUWeY ‘sallaysty Jo neeing °S “9 Jo UOTZEIS VOTSOJOIg UTI “euljoleg §=6 YON ‘Hojnvog *soUdTOG pue sjly jo oynyysuy uATYOoIg ayy jo AloyeIoqey] [eorsoorg “RN ‘soqrey Sunidg plop “AVIS -IAIU() T[eUIOD Jo uolzeIS PPM Teoojorg “AN ‘eoeyyy “Aroyeioqe’y] Tjemsdieyy ‘auTe WW ‘[jeasdievy YyyNog * (penuryuoostp) ‘zissesy sIno'T Aq ¢4gi Ut papunoy vores yeorsojooZ aulleyy asoxueg JO o7IG ‘Sse ‘PURIST 9sextUEg -Aloyeroqge’y [eorsoforg oULIeyA. “SSeP, ‘a]OH] SpOooM ysiiojse ue Aq poyVoIput ore Joye YSelj UO Oso], SNOILVLS GTEId TVOIDOTOIA NVOIMANV WATER F ALL inorganic substances, acting in their own proper nature, and without assist- ance or combination, water ts the most wonderful. If we think of it as the source of all the changefulness and beauty which we have seen in the clouds; then as the instrument by which the earth we have contemplated was modelled into symmetry, and its crags chiseled into grace; then as, in the form of snow, it robes the mountains tt has made, with that transcendent light which we could not have conceived af we had not seen; then as it exists in the foam of the torrent, in the tris which spans tt, in the morning mist which rises from it, in the deep crystalline pools which mirror its hanging shore, in the broad lake and glancing river, finally, in that which ts to all human minds the best emblem of unwearied, unconquerable power, the wild, various, fantastic, tameless unity of the sea; what shall we compare to this mighty, this universal element, for glory and for beauty? or how shall we follow tts eternal cheerfulness of feeling? It is like trying to paint a soul.’’—RUSKIN. 24 CHAPTER II THE NATURE OF AQUATIC ENVIRONMENT PROPERTIES AND USES MIATER, the one abundant =| liquid on earth, is, when pure, tasteless, odorless and transparent. Wa- ter is a solvent of a great variety of sub- stances, both solid and gaseous. Not only does it dissolve more sub- stances than any other liquid, but, what is more important, it dissolves those substances which are most needed in solution for the maintenance of life. Water is the greatest medium of exchange in the world. It brings down the gases from the atmosphere; it transfers ammonia from the air into the soil for plant food; it leaches out the soluble constituents of the soil; and it acts of itself as a chemical agent in nutrition, and also in those changes of putrefaction and decay that keep the world’s available food supply in circulation. Water is nature’s great agency for the applica- tion of mechanical energy. It is by means of water 25 26 Nature of Aquatic Environment that deltas are built and hills eroded. Water is the chief factor in all those eternal operations of flood and floe by which the surface of the continent is shaped. Transparency.—Water has many properties that fit it for being the abode of organic life. Second only in importance to its power of carrying dissolved food materials is its transparency. It admits the light of the sun; and the primary source of energy for all organic life is the radiant energy of the sun. Green plants use this energy directly; animals get it in- directly with their food. Green plants constitute the producing class of organisms in water as on land. Just in proportion as the sun’s rays are excluded, the process of plant assimilation (photosynthesis) is impeded. When we wish to prevent the growth of algae or other green plants in a reservoir or in a spring we cover it to exclude the light. Thus we shut off the power. Pure water, although transparent, absorbs some of the energy of the sun’s rays passed through it, and water containing dissolved and suspended matter (such as are present in all natural water) impedes their passage far more. From which it follows, that the superficial layer of a body of water receives the most light. Penetration into the deeper strata is impeded according to the nature of the water content. Dissolved matters tint the water more or less and give it color. Every one knows that bog waters, for example, are dark. They look like tea, even like very strong tea, and like tea they owe their color to their content of dissolved plant substances, steeped out of the peaty plant remains of the bog. Suspended matters in the water cause it to be turbid. These may be either silt and refuse, washed in from the land, or minute organisms that have grown up in Transparency 27 the water and constitute its normal population. One who has carefully watched almost any of our small northern lakes through the year will have seen that its waters are clearest in February and March, when there is less organic life suspended in them than at other seasons. But it is the suspended inorganic matter that causes the most marked and sudden changes in turbidity—the washings of clay and silt from the hills into a stream; the stirring up of mud from the bottom of a shallow lake with high winds. The difference in clearness of a creek at flood and at low water, or of a pond before and after astormis often very striking. Such sudden changes of turbidity occur only in the lesser bodies of water; there is not enough silt in the world to make the oceans turbid. The clearness of the water determines the depth at which green plants can flourish in it. Hence it is of great importance, and a number of methods have been devised for measuring both color and turbidity. A simple method that was first used for comparing the clearness of the water at different times and places and one that is, for many purposes, adequate, and one that is still used more widely than any other,* consists in the lowering of a white disc into the water and record- ing the depth at which it disappears from view. The standard disc is 20 cm. in diametert; it is lowered in a horizontal position during midday light. The depth at which it entirely disappears from view is noted. It is then slowly raised again and the depth at which it reappears is noted. The mean of these two measurements is taken as the depth of its visibility *Method of Secchi: for other methods, see Whipple’s Microscopy of Drink- ing Water, Chap. V. Steuer’s Planktonkunde, Chapter III. {Whipple varied it with black quadrants, like a surveyor’s level-rod target and viewed it through a water telescope. 28 Nature of Aquatic Environment beneath the surface. Such a disc has been found to disappear at very different depths. Witness the fol- lowing typical examples: Pacific Ocean.... 00... eee ee .59 meters Mediterranean Sea .........-.--- L242 meters Lake Tahoe ..26:40 90 svete) Hepee 33 meters Lake Geneva ... «eee ees pot meters Cayuga. Wake cn 6. avis eee Sate 5 meters Fure Lake (Denmark), Mar ... ee 9 meters Fure Lake (Denmark), Aug. ..... ine 35 meters Fure Lake (Denmark), Dec.... ..... q meters Spoon River (Ill.) underice... ..... 3.65 meters Spoon River (Ill.) at flood ... —..... .o13 meters It is certain that diffused light penetrates beyond the depth at which Secchi’s disc disappears. In Lake Geneva, for example, where the limit of visibility is 21m. photographic paper sensitized with silver chloride ceased to be affected by a 24-hour exposure at a depth of about 100 meters or when sensitized with iodobromide of silver, at a depth about twice as great. Below this depth the darkness appears to be absolute. Indeed it is deep darkness for the greater part of this depth, 90 meters being set down as the limit of ‘‘diffused light.” How far down the light is sufficient to be effective in photosynthesis is not known, but studies of the distri- bution in depth of fresh water algae have shown them to be chiefly confined, even in clear lakes, to the upper- most 20 meters of the water. Ward (’95) found 64 per cent. of the plancton of Lake Michigan in the upper- most two meters of water, and Reighard (’94) found similar conditions in Lake St. Clair. Since the inten- sity of the light decreases rapidly with the increase in depth it is evident that only those plants near the sur- face of the water receive an amount of light comparable with that which exposed land plants receive. Less than this seems to be needed by most free swimming algae, Transparency 29 since they are often found in greatest number in open waters some five to fifteen meters below the surface. Some algae are found at all depths, even in total dark- ness on the bottom; notably diatoms, whose heavy silicious shells cause them to sink in times of prolonged calm, but these are probably inactive or dying individ- uals. There are some animals, however, normally dwelling in the depths of the water, living there upon W0iMeters Depth Fic. 3. Diagram illustrating the penetration of light into the water of a lake; also, its occlusion by inflowing silt and by growths of plants on the surface. the organic products produced in the zone of photo- synthesis above and bestowed upon them in a consider- able measure by gravity. To the consideration of these we will return in a later chapter. The accompanying diagram graphically illustrates the light relationsinalake. The deeper it is the greater its mass of unlighted and, therefore, unproductive water, and the larger it be, the less likely is its upper stratum to be invaded by obscuring silt and water weeds. 30 Nature of Aquatic Environment Mobility—Water is the most mobile of substances, yet it is not without internal friction. Like molasses, it stiffens with cooling to a degree that affects the flotation of micro-organisms and of particles suspended in it. Its viscosity is twice as great at the freezing point as at ordinary summer temperature (77°F .)« Buoyancy—Water is a denser medium than air; it is 775 times heavier. Hence the buoyancy with which it supports a body immersed in it is correspondingly greater. The density of water is so nearly equal to that of protoplasm, that all living bodies will float in it with the aid of very gentle currents or of a very little exertion in swimming. Flying is a feat that only a few of the most specialized groups of animals have mastered, but swimming is common to all the groups. Pressure—This greater density, however, involves greater pressure. The pressure is directly proportional to the depth, and is equal to the weight of the super- posed column of water. Hence, with increasing depth the pressure soon becomes enormous, and wholly insup- portable by bodies such as our own. Sponge fishers and pearl divers, thoroughly accustomed to diving, descending naked from a boat are able to work at depths up to 20 meters. Professional divers, encased in a modern diving dress are able to work at depths several times as great; but such depths, when compared with the depths of the great lakes and the oceans are com- parative shoals. Beyond these depths, however, even in the bottom of the seas, animals live, adjusted to the great pressure, which may be that of several hundred of atmospheres. But these cannot endure the lower pressure of the surface, and when brought suddenly to the surface they burst. Fishes brought up from the bottom of the deeper freshwater lakes, reach the surface greatly Maximum Density 31 swollen, their scales standing out from the body, their eyes bulging. Maximum density—Water contracts on cooling, as do other substances, but not to the freezing point—only to 4° centigrade (39.2° Fahrenheit). On this pecu- liarity hang many important biological consequences. Below 4° C. it begins to expand again, becoming lighter, as shown in the accompanying table: Temperature Weight in lbs. Cc? F° per cu. ft. Density 35 95 62.060 99418 21 70 62.303 -99802 Io 50 62.408 -99975 4 39 62.425 1.00000 ° 32 62.417 -99987 Hence, on the approach of freezing, the colder lighter water accumulates at the surface, and the water at the point of maximum density settles to the bottom, and the congealing process, so fatal to living tissues generally is resticted to a thin top layer. Here at 0° C. (32° F.) the water freezes, expanding about one-twelfth in bulk in the resulting ice and reducing its weight per cubic foot to 57.5 pounds. Stratification of the water—Water is a poor conductor of heat. We recognize this when we apply heat to the bottom of a vessel, and set up currents for its distribution through the vessel. We depend on convection and not on conduction. But natural bodies of water are heated and cooled from the top, when they are in contact with the atmosphere and where the sun’s rays strike. Hence, it is only those changes of temperature which increase the density of the surface waters that can pro- duce convection currents, causing them to descend, and deeper waters to rise in their place. Minor changes of this character, very noticeable in shallow water, occur 32 Nature of Aquatic Environment every clear day with the going down of the sun, but great changes, important enough to effect the tempera- ture of all the waters of a deep lake, occur but twice a year, and they follow the procession of the equinoxes. There is a brief, often interrupted, period (in March in the latitude of Ithaca) after the ice has gone out, while the surface waters are being warmed to 0°C.; and there is a longer period in autumn, while they are being cooled to o°C. Between times, the deeper waters of W/NTER SUMMER METERSS 2S rs 3 Fic. 4. Diagram illustrating summer and winter temperature conditions in Cayuga Lake. The spacing of the horizontal lines represents equal temperature intervals. a lake are at rest, and they are regularly stratified according to their density. In deep freshwater lakes the bottom temperature remains through the year constantly near the point of maximum density, 4° C. This is due to gravity. The heavier water settles, the lighter, rises to the top. Were gravity alone involved the gradations of tempera- ture from bottom to top would doubtless be perfectly regular and uniform at like depths from shore to shore. But springs of ground water and currents come in to Lake Temperatures 33 disturb the horizontal uniformity, and winds may do much to disturb the regularity of gradations toward the surface. Water temperatures are primarily dependent on those of the superincumbent air. The accompany- ing diagram of comparative yearly air and water temperatures in Hallstatter Lake (Austria) shows graphically the diminishing influence of the former on the latter with increasing depth. eo | S}-c] &} &|] 2] BIS tS) els] c dla] a) so] & 3) 2) *o] S| 3 C S| =| ES] 3/3) 13/5) 2/8 75 4 a = re) /0 + J & wy iy S| 54 yf 4 § wa FS & ae, ~ ss S — & lo4 = | Pt | 4 NY] 54 az ~ | 1| o4 4 10 e cams Olli (NGS eae oe v4 + 17 Slo 4 10+ ees ae an Ga | o4 — fT ata re -— .——-4} - — Jd4 ~ a a JO} o4 a v4 +] | + 7 60} o4 J — 100) 0O- 4 Fic. 5. Diagram illustrating the relation of air and water temperatures at varying depths of water in Hallstatter Lake (after Lorenz). 34 Nature of Aquatic Environment Fic. 6. Diagram illustrating the distribution of temperature in Cayuga Lake throughout the year. The yearly cycle—The general relation between sur- face and bottom temperatures for the year are graphi- cally shown in the accompanying diagram, wherein the two periods of thermal stratification, ‘‘direct’’ in summer when the warmer waters are uppermost, and “‘znverse’”’ in winter when the colder waters are uppermost, are separated by two periods of complete circulation, when all the waters of the lake are mixed at 4° C. The range of temperatures from top to bottom is much greater in the summer “‘stagnation period’’; nevertheless there The Yearly Cycle 35 is more real stagnation during the winter period; for, after the formation of a protecting layer of ice, this shuts out the disturbing influence of wind and sun and all the waters are at rest. The surface temperature bears no further relation to air temperature but remains constantly at o° C. After the melting of the ice in late winter the surface waters begin to grow warmer; so, they grow heavier, and tend to mingle with the underlying waters. When all the water in the lake is approaching maximum density strong winds heaping the waters upon a lee shore, may put the entire body of the lake into complete circulation. How long this circulation lasts will depend on the weather. It will continue (with fluctuating vigor) until the waters are warm enough so that their thermal stratification and consequent resistance to mixture are great enough to overcome the disturbing influence of the wind. Thereafter, the surface may be stirred by storms at any time, but the deeper waters of the lake will have passed into their summer rest. On the approach of autumn the cooling of surface waters starts convection currents, which mix at first the upper waters only, but which stir ever more deeply as the temperature descends. When nearly 4°C., with the aid of winds, the entire mass of water is again put in circulation. The temperature is made uniform throughout, and what is more important biologically, the contents of the lake, in both dissolved and suspended matters, are thoroughly mixed. Nothing is thereafter needed other than a little further cooling of the surface waters to bring about the inverse stratification of the winter period. Vernal and autumnal circulation periods differ in this, that convection currents have a smaller share, and winds may have a larger share in the former. For the surface waters are quickly warmed from 0° C. to 4° C., 36 Nature of Aquatic Environment and further warming induces no descending currents, but instead tends toward greater stability. It some- times happens that in shallow lakes there is little vernal circulation. If the water be warmed at 4° C. at the bottom before the ice is entirely gone, and if a period of calm immediately follow, so that no mixing is done by the wind, there may be no general spring circulation whatever. The shallower the lake, other things being equal, the greater will be the departure of temperature conditions from those just sketched, for the greater will be the disturbing influence of the wind. In south temperate lakes, temperature conditions are, of course, reversed with the seasons. In tropical lakes whose surface temperature remains always above 4° C., there can be no complete circulation from thermal causes, and in- verse stratification is impossible. In polar lakes, never freed from ice, no direct stratification is possible. It follows from the foregoing that gravity alone may do something toward the warming of the waters in the spring, and much toward the cooling of them in the fall. By gravity they will be made to circulate until they reach the point of maximum density, when going either up or down the scale. Beyond this point, however, gravity tends to stabilize them. The wind is responsi- ble for the further warming of the waters in early sum- mer, and the heat in excess of 4° C. has been called by Birge and Juday ‘‘wind-distributed”’ heat. They esti- mate that it may amount to 30,000 gram-calories per square centimeter of surface in such lakes as those of Central New York, and the following figures for Cayuga Lake show its distribution by depth in August, IQII, in percentage remaining at successive ten-meter intervals below the surface: Below o 10 20 30 40 50 60 70 80 100 133 meters % 100 50.2 16.7 7.1 3.7 2.4 1.8 1.2 .7 .3. remaining Thermocline 37 These figures indicate the resistance to mixing that gravity imposes, and show that the wind is not able to overcome it below rather slight depths. Vernal and autumnal periods of circulation have a very great influence upon the distribution of both organisms and their food materials in a lake; to the consideration of this we will have occasion to return later. The thermocline—In the study of lake temperatures at all depths, a curious and interesting peculiarity of temperature interval has been commonly found per- taining to the period of direct stratification (mid- summer). The descent in temperature is not regular from surface to bottom, but undergoes a sudden acceler- ation during a space of a very few meters some distance below the surface. The stratum of water in which this sudden drop of temperature occurs is known as the thermocline (German, Sprungschicht). It appears to represent the lower limit of the intermittent summer circulation due to winds. Above it the waters are more or less constantly stirred, below it they lie still. This interval is indicated by the shading on the right side of figure 4. Birge has designated the area above the thermocline as the epilimnion; the one below it as hypolimnion. Further study of the thermocline has shown that it is not constant in position. It rises nearer to the surface at the height of the midsummer season and descends a few meters with the progress of the cooling of the autumnal atmosphere. This may be seen in figure 7, which is Birge and Juday’s chart of temperatures of Lake Mendota as followed by them through the season of direct stratification and into the autumnal circula- tion period in 1906. This chart shows most graphically the growing divergence of surface and bottom tempera- tures up to August, and their later approximation and 38 Nature of Aquatic Environment final coalescence in October. Leaving aside the not unusual erratic features of surface temperature (repre- sented by the topmost contour line) it will be noticed that there is a wider interval somewhere between 8 and 16 meters than any other interval either above or below it. Sometimes it falls across two spaces and is rendered less apparent in the charting by the selection of inter- vals. It first appears clearly in June at the 10-12 meter interval. It rises in July above the 10 meter level. T MAY JUNE JULY AUG SEPT. . oc’ 1 Fic. 7. Temperature of the water at different depths in Lake Mendota in 1906. The vertical spaces represent degrees Centigrade and the figures attached to the curves indicate the depths in meters. (Birge and Juday). In the middle of August it lies above the 8 meter level, though it begins to descend later in the month. It continues to descend through September, and is found in early October between 16 and 18 meters. It dis- appears with the beginning of the autumnal circulation. The cause of this phenomenon is not known. Richter has suggested that convection currents caused by the nocturnal cooling of the surface water after hot summer days may be the cause of it. If the surface waters were Circulation 39 cooled some degrees they would descend, displacing the layers underneath and setting up shallow currents which would tend to equalize the temperature of all the strata involved therein. And if the gradation of tem- peratures downward were regular before this mixing, the result of it would be a sudden descent at its lower limit, after the mixing was done. This would account for the upper boundary of the thermocline, but not for its lower one. Perhaps an occasional deeper mixing, extending to its lower boundary, and due possibly to high winds, might bring together successional lower levels of temperature of considerable intervals. Perhaps the thermocline is but an accumulation of such sort of thermal disturbance-records, ranged across the vertical section of the lake, somewhat as wave-drift is ranged in a shifting zone along the middle of a sloping beach. At any rate, it appears certain that the thermocline marks the lower limit of the chief disturbing influences that act upon the surface of the lake. That it should rise with the progress of summer is probably due to the increasing stability of the lower waters, as differences in temperature (and therefore in density) between upper and lower strata are increased. Resistance to mixing increases until the maximum temperature is reached, and thereafter declines, as the influence of cooling and of winds penetrates deeper and deeper. In running water the mixing is more largely mechani- cal, and vertical circulation due to varying densities is less apparent. Yet the deeper parts of quiet streams approximate closely to conditions found in shallow lakes. Such thermal stratification as the current permits is direct in summer and inverse in winter, and there are the same intervening periods of thermal over- turn when the common temperature approaches 4° C. In summer and in winter there is less ‘‘stagnation”’ of bottom waters owing to the current of the stream. 40 Nature of Aquatic Environment The thermal conservatism of water—Water is slower to respond to changes of temperature than is any other known substance. Its specific heat is greater. The heat it consumes in thawing (and liberates in freezing) is greater. The amount of heat necessary to melt one part of ice at 0° C. without raising its temperature at all would be sufficient to raise the temperature of the same when melted more than 75 degrees. Furthermore, the heat consumed in vaporization is still greater. The amount required to vaporize one part of water at 100° C. without raising its temperature would suffice to raise 534 parts of water from 0° C. to 1° C.; and the amount is still greater when vaporization occurs at a lower temperature. Hence, the cooling effect of evaporation on the surrounding atmosphere, which gives up its heat to effect this change of state in the water; hence, the equalizing effect upon climate of the presence of large bodies of water; hence the extreme variance between day and night temperatures in desert lands; hence the delaying of winter so along after the autumnal, and of summer so long after the vernal equinox. Water is the great stabilizer of temperature. The content of natural waters—Water is the common solvent of all foodstuffs. These stuffs are, as every- body knows, such simple mineral salts as are readily leached out cf the soil, and such gases as may be washed down out of the atmosphere. And since green plants are the producing class among organisms, all others being dependent on their constructive activities, water is fitted to be the home of life in proportion as it con- tains the essentials of green plant foods, with fit condi- tions of warmth, air and light. Natural waters all contain more or less of the elemen- tary foodstuffs necessary for life. Pure water (H,O) is not found. All natural waters are mineralized waters—even rain, as it falls, is such. And a compara- Natural Waters 4I tively few soluble solids and gases furnish the still smaller number of chemical elements that go to make up the living substance. The amount of dissolved solids varies greatly, being least in rainwater, and greatest in dead seas, which, lacking outlet, accumulate salts through continual evaporation. Here is a rough statement of the dissolved solids in some typical waters: Inrain water......... .... aa 30— 40 parts per million In drainage water off siliceous soils so— 8o “ “ In springs flowing from siliceous soils 60— 250 “ “ “* In drainage water off calcareous soils 140— 230 en In springs flowing from calcareous soils .. 1... nad. -Sycke bes 300— 660 “ “ « Inriversatlarge .... ..... . I20—~— 350 “ “ & Intheocean ... ..... ..... 33000—37370 “ “ “© Thus the content is seen to vary with the nature of the soils drained, calcareous holding a larger portion of soluble solids than siliceous soils. It varies with presence or absence of solvents. Drainage waters from cultivated lands often contain more lime salts than do springs flowing from calcareous soils that are deficient in carbon dioxide. Spring waters are more highly charged than other drainage waters, because of pro- longed contact as ground water with the deeper soil strata. And evaporation concentrates more or less the content of all impounded waters. All natural waters contain suspended solids in great variety. These are least in amount in the well filtered water of springs, and greatest in the water of turbu- lent streams, flowing through fine soils. At the con- fluence of the muddy Missouri and the clearer Mississippi rivers the waters of the two great currents may be seen flowing together but uncommingled for miles. The suspended solids are both organic and inorganic, and the organic are both living and dead, the latter 42 Nature of Aquatic Environment being plant and animal remains. From all these non- living substances the water tends to free itself: The lighter organic substances (that are not decomposed and redissclved) are cast on shore; the heavier mineral substances settle to the bottom. The rate of settling is dependent on the rate of movement of the water and on the specific gravity and size of the particles. Fall Creek at Ithaca gives a graphic illustration of the carry- ing power of the current. In the last mile of its course, included between the Cornell University Campus and Cayuga Lake, it slows down gradually from a sheer descent of 78 ft. at the beautiful Ithaca Fall to a scarcely perceptible current at the mouth. It carries huge blocks of stone over the fall and drops them at its foot. It strews lesser blocks of stone along its bed for a quar- ter of a mile to a point where the surface ceases to break in riffles at low water. There it deposits gravel, and farther along, beds and bars of sand, some of which shift position with each flood rise, and consequent acceleration. It spreads broad sheets of silt about its mouth and its residual burden of finer silt and clay it carries out into the lake. The lake acts as a settling basin. Flood waters that flow in turbid, pass out clear. Whipple has given the following figures for rate of settling as determined by size, specific gravity and form being constant: Velocity of particles falling through water Diameter 1. inch, falls roo. feet per minute. “se 4c ini oe tas “ oI, 8. “ec .OL “ cc 15 ae cé ae ins .OOL “ce [ai .OOTS ae oe “ce ae ,OOOI ing oe .OOOOIS izs Las “ce Suspended mineral matters are, as a rule, highly insoluble. Instead of promoting, they lessen the productivity of the water by shutting out the light. Gases from the Atmosphere 43 Suspended organic solids likewise contribute nothing to the food supply as long as they remain undissolved. But when they decay their substance is restored to circulation. Only the dissolved substances that are in the water are at once available for food. The soil and the atmosphere are the great storehouses of these materials, and the sources from which they were all originally derived. Gases from the atmosphere—The important gases derived from the atmosphere are two: carbon dioxide (CO.) and oxygen (O). Nitrogen is present in the atmosphere in great excess (N, 79% to O, nearly 21%, and CO,, .03%), and nitrogen is the most important constituent of living substance, but in gaseous form, free or dissolved, it is not available for food. The capacity of water for absorbing these gases varies with the temperature and the pressure, diminishing as warmth increases (insomuch that by boiling they are removed from it), and increasing directly as the pres- sure increases. Pure water at a pressure of 760 mm. in an atmosphere of pure gas, absorbs these three as follows: Oxygen CO2 Nitrogen At o°CS AI.14 1796.7 20.35 At 20°C 28.38 QO1.4 14.03 At double the pressure twice the quantity of the gas would be dissolved. Natural waters are exposed not to the pure gas but to the mixture of gases which make up the atmosphere. In such a mixture the gases are absorbed independently of each other, and in propor- tion to their several pressures, which vary as their several densities: the following table* shows, for *Abridged from a table of values to tenths of a degree by Birge and Juday in Bull. 22, Wisc. Geol. & Nat. Hist. Survey, p. 20. 44 Nature of Aquatic Environment example, the absorbing power of pure water at various temperatures for oxygen from the normal atmosphere at 760 mm. pressure: Waterat o°C 9.70 cc. per liter at 15°C 6.96 cc. per liter ne BoC. B.68'Ce, “20°C 6.28cc. “ * ing 10°C 7.97 ce. 46 ind oe 25°C 5-76 ce. zi oc The primary carbon supply for the whole organic world is the carbon dioxide (CO,) of the atmosphere. Chlorophyll-bearing plants are the gatherers of it. They alone among the organisms are able to utilize the energy of the sun’s rays. The water existing as vapor in the atmosphere is the chief agency for bringing these gases down to earth for use. Standing water absorbs them at its surface but slowly. Water vapor owing to better exposure, absorbs them to full saturation, and then descends as rain. In fresh water they are found in less varying proportion, varying from none at all to con- siderable degree of supersaturation. Birge and Juday report a maximum occurrence of oxygen as observed in the lakes of Wisconsin of 25.5 cc. per liter in Knight’s Lake on Aug. 26, 1909 at a depth of 4.5 meters. This water when brought to the surface (with consequent lowering of pressure by about half an atmosphere) burst into lively effervescence, with the escape of a considerable part of the excess oxygen into the air. (II, p. 52). They report the midsummer occurrence of free carbon dioxide in the bottom waters of several lakes in amounts approaching 15 cc. per liter. The reciprocal relations of CO. and O—Carbon dioxide and oxygen play leading roles in organic metabolism, albeit, antithetic roles. The process begins with the cleavage of the carbon dioxide, and the building up of its carbon into organic compounds; it ends with the oxidation of effete carbonaceous stuffs and the reappear- ance of CO.. Both are used over and over again. - Carbon Dioxide and Oxygen 45 Plants require CO, and animals require oxygen in order to live and both live through the continual exchange of these staple commodities. This is the best known phase in the cycle of food materials. The oxygen is freed at the beginning of the synthesis of organic mat- ter, only to be recombined with the carbon at the end of its dissolution. And the well-being of the teeming population of inland waters is more dependent on the free circulation and ready exchange of the dissolved supply of these two gases than on the getting of a new supply from the air. The stock of these gases held by the atmosphere is inexhaustible, but that contained in the water often runs low; for diffusion from the air is slow, while consumption is sometimes very rapid. We often have visible evidence of this. In the globe in our win- dow holding a water plant, we can see when the sun shines streams of minute bubbles of oxygen, arising from the green leaves. Or, in a pond we can see great masses of algae floated to the surface on a foam of oxygen bubbles. We cannot see the disappearance of the carbon dioxide but if we test the water we find its acidity diminishing as the carbon dioxide is con- sumed. At times when there is abundant growth of algae near the surface of a lake there occurs a most instructive diurnal ebb and flow in the production of these two gases. By day the well lighted layers of the water become depleted of their supply of CO, through the photosynthetic activities of the algae, and become supersaturated with the liberated oxygen. By night the microscopic crustaceans and other plancton animals rise from the lower darker strata to disport themselves nearer the surface. These consume the oxygen and restore to the water an abundance of carbon dioxide. And thus when conditions are right and the numbers of 46 Nature of Aquatic Environment plants and animals properly balanced there occur regular diurnal fluctuations corresponding to their respective periods of activity in these upper strata. Photosynthesis is, however, restricted to the better lighted upper strata of the water. The region of greatest carbon consumption is from one to three meters in depth in turbid waters, and of ten meters or more in depth in clear lakes. Consumption of oxygen, however, goes on at all depths, wherever animal respiration or organic decomposition occurs. And decomposition occurs most extensively at the bottom where the organic remains tend to be accumulated by gravity. With a complete circulation of the water these two gases may continue to be used over and over again, as in the exam- ple just cited. But, as we have seen, there is no circula- tion of the deeper water during two considerable periods of the year; and during these stagnation periods the distribution of these gases in depth becomes correlated in a wonderful way with the thermal stratification of the water. This has been best illustrated by the work of Birge and Juday in Wisconsin. Figure 8 is their diagram illustrating the distribution of free oxygen in Mendota Lake during the summer of 1906. It should be studied in connection with figure 7, which illustrates conditions of temperature. Then it will be seen that the two periods of equal supply at all levels correspond to vernal and autumnal circulation periods. The season opens with the water nearly saturated (8 cc. of oxygen per liter of water) throughout. With the warm- ing of the waters the supply begins to decline, being consumed in respiration and in decomposition. In the upper six or seven meters the decline is not very exten- sive, for at these depths the algae continually renew the supply. But as the lower strata settle into their sum- mer rest their oxygen content steadily disappears, and 1s not renewed until the autumnal overturn. For three Summer Stagnation 47 months there is no free oxygen at the bottom of the lake, and during August there is not enough oxygen below the ten meter level to keep a fish alive. Correspondingly, the amount of free CO, in the deeper strata of the lake increases rather steadily until the autumnal overturn. It is removed from circulation, and in so far as it is out of the reach of effective light, it is unavailable for plant food. MAY JUNE JULY AUG. L s) Pore P i Fic. 8. Dissolved oxygen at different depths in La ; vertical spaces represent cubic centimeters of gas per liter of water and the figures attached to the curves indicate the depths in meters. (Birge and Juday.) Other gases—A number of other gases are more or less constantly present in the water. Nitrogen, as above stated, being absorbed from the air, methane (CH,), and other hydrocarbons, and hydrogen sulphide (H.S), etc., being formed in certain processes of decom- 48 Nature of Aquatic Environment position. Of these, methane or marsh gas, 1S perhaps the most important. This is formed where organic matter decays in absence of oxygen. In lakes such conditions are found mainly on the bottom. In marshes and stagnant shoal waters generally, where there is much accumulation of organic matter on the bottom, this gas is formed in abundance. It bubbles up through the bottom ooze, or often buoys up rafts of agglutinated bottom sediment. Nitrogen—The supply of nitrogen for aquatic organ- isms is derived from soluble simple nitrates (KNO:;, NaNO,, etc.) Green plants feed on these, and build proteins out of them. And when the plants die (or when animals have eaten them) their dissolution yields two sorts of products, ammonia and nitrates, that become again available for plant food. Ammonia is produced early in the process of decay and the nitrates are its end products. Bacteria play a large role in the decomposition of proteins. Atleast four groups of bacteria successively participate in their reduction. The first of these are concerned with the liquefaction of the proteins, hydroly- zing the albumins, etc., by successive stages to albu- moses, peptones, etc., and finally to ammonia. A second group of bacteria oxidizes the ammonia to nitrites. A third group oxidizes the nitrites to nitrates. A fourth group, common in drainage waters, reduces nitrates to nitrites. Since these processes are going on side by side, nitrogen is to be found in all these states of combination when any natural water is subjected to chemical analysis. The following table shows some of the results of a large number (415) of analyses of four typical bottomland bodies of water, made for Kofoid’s investigation of the plancton of the Illinois River by Professor Palmer. Nitrogen 49 The relative productiveness in open-water life of these situations is shown in the last column of the table. In parts Solids Planct per million Sus- Dis- Free Organic | Nitrites | Nitrates ee bert pended | solved Ammonia| Nitrogen ™3 Illinois River .| 61.4 |304.1 | .860 | 1.03 | .147 | 1.59 | 1.91 Spoon River .| 274.3 |167.1 | .245 | 1.29 | .039 | I.o1 39 Quiver Lake .| 25.1 | 248.2 | .165 61 | .023 .66 | 1.62 Thompson’s L.| 44.6 | 282.9 | .422 | 1.05 | .048 .64 | 6.68 The difference between these four adjacent bodies of water explains some of the peculiarities of the table. The rivers hold more solids in suspension than do the lakes, although these lakes are little more than basins holding impounded river waters. Spoon River holds the least amount of dissolved solids, and by far the greatest amount of suspended solids. Since the latter are not available for plant food, naturally this stream is least productive of plancton. Illinois River drains a vast and fertile region, and receives in its course the sewage and other organic wastes of two large cities, Chicago and Peoria, and of many smaller ones. Hence, its high content of dissolved matter, the cities being remote, so there has been time for extensive liquefac- tion. Hence, also, its high content of ammonia, of nitrites and of nitrates. The two lakes are very unlike; Quiver Lake is a mere strip of shoal water, fed by a clear stream that flows in through low sandy hills. It receives water from the Illinois River only during high floods. Thompson's Lake is a much larger body of water, fed directly from the Illinois River through an open channel. Naturally, it is much like the river in its dissolved solids, and in its total organic nitrogen. That it falls far below the river in nitrates and rises high above it in plancton production may perhaps be due to the extensive con- 50 Nature of Aquatic Environment sumption of nitrates by plancton algae. Nitrates, be- cause they furnish nitrogen supply in the form at once available for plant growths, are, in shallow waters at least, an index of the fertility of the water. As on land, so in the water, the supply of these may be inadequate for maximum productiveness, and they may be added with profit as fertilizer. The carbonates—Lime and magnesia combine with carbon dioxide, abstracting it from the water, forming — NAVANA Fic. 9. Environs of the Biological Field Station of the Illinois State Labora- tory of Natural History, the scene of important work by Kofoid and others on the life of a great river. solid carbonates (CaCO; and MgCO;). These accumu- late in quantities in the shells of molluscs, in the stems of stoneworts, in the incrustations of certain pond weeds, and of lime-secreting algae. The remains of such organisms accumulate as marl upon the bottom. The carbonates (and other insoluble minerals) remain; the other body compounds decay and are removed. By such means in past geologic ages the materials for the earth’s vast deposits of limestone were accumu- The Carbonates 51 lated. Calcareous soils contain considerable quantities of these carbonates. In pure water these simple carbonates are practically insoluble; but when carbon dioxide is added to the water, they are transformed into bicarbonates* and are readily dissolved. So the carbonates are leached out of the soils and brought back into the water. So, the solid limestone may be silently removed, or hollowed out in great caverns by little underground streams. So the Mammoth Cave in Kentucky, and others in Cuba, in Missouri, in Indiana and elsewhere on the continent, have been formed. The water gathers up its carbon dioxide in part as it descends through the atmosphere, and in larger part as it percolates thro soil where decomposition is going on and where oxidation products are added to it. Carbon dioxide, thus exists in the water in three conditions: (1) Fixed (and unavailable as plant food) in the simple carbonates; (2) “half-bound”’ in the bicarbonates; and (3) free. Water plants use first for food, the free carbon dioxid, and then the ‘‘half bound”’ that is in loose combination in the bicarbonates. As this is used up the simple carbonates are released, and the water becomes alkaline.§ Birge and Juday have several times found a great growth of the desmid Staurastrum associated with alkalinity due to this cause. In a maximum growth which occurred in alkaline waters at a depth of three meters in Devil’s Lake, Wisconsin, on June 15th, 1907, these plants numbered 176,000 per liter of water. *CaCOs, for example, becoming Ca(HCOs)2, the added part of the formula representing a molecule each of CO2z and H20. yIf “hard” water whose hardness is due to the presence of these bicarbonates be boiled, the COs is driven off and the simple carbonates are re-precipitated (as, for example, on the sides and bottom of a tea kettle). This is “temporary hardness.” ‘‘Permanent hardness” is due to the presence of sulphates and chlorides of lime and magnesia, which continue in solution after boiling. §Phenolphthalein, being used as indicator of alkalinity. 52 Nature of Aquatic Environment Waters that are rich in calcium salts, especially in calcium carbonate, maintain, as a rule,a more abundant life than do other waters. Especially favorable are they to the growth of those organisms which use much lime for the building of their hard parts, as molluscs, stoneworts, etc. There are, however, individual pref- erences in many of the larger groups. The crustaceans for example, prefer, as a rule, calcium rich waters, but one of them, the curious entomostracan, Holopedium gibberum, (Fig. 10) is usually found in calcium poor waters, in lakes in the Rocky Mountains and in the Adiron- dacks, in waters that flow off archean rocks or out of silic- eous sands. The desmids with few exceptions are more abundant in calcium poor waters. The elegant genus micrasterias is at Ithaca espec- : ; ially abundant in the peat- T10.,A selatinous-costed mi stained calcium-poor waters berum, often found in waters of sphagnum b ogs. that are poor in calcium. Other minerals in the water—The small quantities of other mineral substances required for plant growth are furnished mainly by a few sulphates, phosphates and chlorids: sulphates of sodium, potassium, calcium and magnesium; phosphates of iron, aluminum, cal- cium and magnesium, and chlorids of sodium, potas- sium, calcium and magnesium. Aluminum alone of the elements composing the above named compounds, is not always requisite for growth, although it is-very often present. Silica, likewise, is of wide distribution, and occurs in the water in considerable amounts, and is used by many organisms in the growth of their hard parts. As the stoneworts use lime for their growth, some 4% of the dry weight of Chara being CaO, so Mineral Content 53 diatoms require silica to build their shells. When the diatoms are dead their shells, relatively heavy though extremely minute, slowly settle to the bottom, slowly dissolving; and so, analyses of lake waters taken at different depths usually show increase of silica toward the bottom. Iron, common salt, sulphur, etc., often occur locally in great abundance, notably in springs flowing from special deposits, and when they occur they possess a fauna and flora of marked pecu- liarities and very limited extent. An idea of the rela- tive abundance of the commoner mineral substances in lake waters may be had from the following figures that are con- densed from Birge and Fic. 11. A beautiful green desmid, Micra- i stertas that is common in bog waters. J uday s report of 74 analyses. MINERAL CONTENT OF WISCONSIN LAKES Parts per million Fl203 + SiO. AljO; Ca Mg Na K CO3 HCOs SO. Cl Minimum 0.8 04 0.6 0.3 0.3 0.3 0.0 49 O00 I.5 Maximum 33.0 11.2 49.6 32.7 6.2 3.1 12.0 153.0 18.7 10.0 Average 11.7 2.1 26.9 19.6 3.2 2.2 2.1 91.7 9-8 3.9 This is the bill of fare from which green water plants may choose. Forel aptly compared the waters of a 54 Nature of Aquatic Environment lake to the blood of the animal body. As the cells of the body take from the blood such of its content as is suited to their need, so the plants and animals of the water renew their substance out of the dissolved sub- stances the water brings to them. Organic substances dissolved in the water may so affect both its density and its viscosity as to determine both stratification and distribution of suspended solids. This is a matter that has scarcely been noticed by limnologists hitherto. Dr. J. U. Lloyd (’82) long ago showed how by the addition of colloidal substances to a vessel of water the whole contents of the vessel can be broken into strata and these made to circulate, each at its own level, independent of the other strata. Solids in suspension can be made to float at the top of particu- lar strata, according to density and surface tension. Perhaps the “‘false bottom’’ observed in some north- ern bog-bordered lakes is due to the dissolved colloids of the stratum on which it floats. Holt (’08, p. 219) describes the ‘‘false bottom’’ in Sumner Lake, Isle Royal, as lying six to ten feet below the surface, many feet above the true bottom; as being so tenuous that a pole could be thrust through it almost as readily as through clear water; and as being composed of fine disintegrated remains of leaves and other light organic material. “In places there were great breaks in the ‘false bottom,’ doubtless due to the escape of gases which had lifted this fine ooze-like material from a greater depth: and through these breaks one could look down several feet through the brownish colored water.” Perhaps the colloidal substances in solution are such as harden upon the surface of dried peat, likea water-proof glue, making it for a time afterward imper- vious to water. WATER AND LAND CEANS are the earth’s great storehouse of water. They cover some eight- elevenths of the surface of the earth to an average depth of about two miles. They receive the off-flow from all the continents and send it back by way of the atmosphere. The fresh waters of the earth descend in the first instance out of the atmosphere. They rise in vapor from the whole surface of the earth, but chiefly from the ocean. Evaporation frees them from the ocean’s salts, these being non-volatile. They drift about with the currents of the atmosphere, gathering its gases to saturation, together with very small quantities of drift- ing solids; they descend impartially upon water and land, chiefly as rain, snow and hail. They are not distributed uniformly over the face of the continents for each continent has its humid regions and its deserts. Rainfall in the United States varies from 5 to 100 inches per annum. Two-thirds of it falls on the eastern three-fifths of the country. For the Eastern United States it averages about 48 inches, for the Western United States about 12 inches; the average for the whole is about 30 inches. The total annual precipitation is about 5,000,000,000 acre-feet.* ~ *An acre-foot is an acre of water 1 foot deep or 43,560 cubic feet of water. 55 56 Water and Land It is commonly estimated that at least one-half of this rainfall is evaporated, in part from soil and water surfaces, but much more from growing vegetation; for the transpiration of plants gives back immense quanti- ties of water to the atmosphere. Hellriegel long ago showed that a crop of corn requires 300 tons of water per acre: of potatoes or clover, 400 tons per acre. At the Iowa Agricultural Experiment Station it was shown that an acre of pasturage requires 3,223 tons of water, or 28 inches in depth (21% acre-feet). Before the days of tile drainage it was a not uncommon practice to plant willow trees by the edges of swales, in order that they might carry off the water through their leaves, leaving the ground dry enough for summer cropping. The rate of evaporation is accelerated also, by high temperatures and strong winds. \ The rain tends to wet the face of the ground every- where. How long it will stay wet in any given place will depend on topography and on the character of the soil as well as on temperature and air currents. Show- ers descending intermittently leave intervals for com- plete run-off of water from the higher ground, with opportunity for the gases of the atmosphere to enter and do their work of corrosion. The dryer intervals, therefore, are times of preparation of the materials that will appear later in soil waters. Yet all soils in humid regions retain sufficient moisture to support a considerable algal flora. Periodical excesses of rainfall are necessary also to maintain the reserve of ground water in the soil. Suppose, for example, that the 35 inches of annual rainfall at Ithaca were uniformly distributed. There would be less than one-tenth of an inch of precipitation each day—an amount that would be quickly and entirely evaporated, and the ground would never be thoroughly wet and there would be no ground water to replenish the streams. Storm waters Soil and Stream-flow 57 tend to be gathered together in streams, and thus about one-third of our rainfall runs away. In humid areas small streams converge to form larger ones, and flow onward to the seas. In arid regions they tend to spread out in sheet floods, and to disappear in the sands. In a state of nature little rain water runs over the surface of the ground, apart from streams. It mainly descends into the soil. How much the soil can hold depends upon its composition. Dried soils have a capacity for taking up and holding water about as fol- lows: sharp sand 25%, loam 50%, clay 60%, garden mould 90% and humus 180% of their dry weight. Water descends most rapidly through sand and stands longest upon the surface of pure clay. Thick vegetation with abundant leaf fall, and humus in the soil tend to hinder run-off of storm waters, and to prolong their passage through the soil. Thus the excess of rainfall is gradually fed into the streams by springs and seepage. Under natural conditions streams are usually clear, and their flow is fairly uniform. Unwise clearing of the land and negligent cultivation of the soil facilitate the run-off of the water before the storm is well spent, promote excessive erosion and render the streams turbid and their volume abnormally fluctuating. Little water enters the soil and hence the springs dry up, and the brooks, also, as the seepage of ground water ceases. Two great evils immediately befall the creatures that live in the streams and pools: (1) There is wholesale direct extermination of them with the restriction of their habitat at low water. (2) There occurs smothering of them under deposits of sediment brought down in time of floods, with indirect injury to organisms not smothered, due to the damage to their foraging grounds. The waters of normal streams are derived mainly from seepage, maintained by the store of water accumu- 58 Water and Land lated in the soil. This store of ground water amounts according to recent estimates to some 25% of the bulk of the first one hundred feet in soil depth. Thus it equals a reservoir of water some 25 feet deep covering the whole humid eastern United States. It is con- tinuous over the entire country. Its fluctuations are studied by means of measurements of wells, especially by recording the depth of the so-called ‘‘water table.”’ On the maintenance of ground water stream-flow and organic productiveness of the fields alike depend. CHAPTER III TYPES OF AQUATIC ENVIRONMENT I. LAKES AND PONDS M™® (UT of the atmosphere ‘| comes our water supply —the greatest of our natural resources. It falls on hill and dale, and mostly descends into the soil. The ex- cess off-flowing from the surface and outflowing from springs and seepage, forms water masses of various sorts according to the topo- graphy of the land surface. It forms lakes, streams or marshes according as there occur basins, channels or only plant accumulations influencing drainage. The largest of the bodies of water thus formed are the lakes. Our continent is richly supplied with them, but they are of very unequal distribution. The lake regions in America as elsewhere are regions of compara- tively recent geological disturbance. Lakes thickly dot the peninsula of Florida, the part of our continent most recently lifted from the sea. Over the northern recently glaciated part of the continent they are 59 60 Types of Aquatic Environment innumerable, but in the great belts of corn and cotton, and on the plains to the westward, they are few and far between. They are abundant in the regions of more recent volcanic disturbance in our western mountains, but are practically absent from the geologically older Appalachian hills. They lie in the depressions between the recently uplifted lava blocks of southern Oregon. They occur also in the craters of extinct volcanoes. They are apt to be most picturesque when their setting is in the midst of mountains. There are probably no more beautiful lakes in the world than some of those in the West, such as Lake Tahoe (altitude 6200 ft.) on the California-Nevada boundary, and Lake Chelan in the state of Washington*, to say nothing of the Coeur d’Alene in Idaho and Lake Louise in British Columbia. Eastward the famous lake regions that attract most visitors are those of the mountains of New York and New England, those of the woodlands of Michigan and Wisconsin and those of the vast areas of rocks and water in Canada. Lakes are temporary phenomena from the geologists point of view. No sooner are their basins formed than the work of their destruction begins. Water is the agent of it, gravity the force employed, and erosion the chief method. Consequently, other things being equal, the processes of destruction go on most rapidly in regions of abundant rainfall. Inwash of silt from surrounding slopes tends to fill up their basins. The most extensive filling is about the mouths of inflowing streams, where mud flats form, and extend in Deltas out into the lake. These deltas are the exposed sum- mits of great mounds of silt that spread out broadly underneath the water on the lake floor. At the shore- lines these deposits are loosened by the frosts of winter, *Descriptions of these two lakes will be found in Russell’s Lakes of North America. Lakes Temporary Phenomena 61 pushed about by the ice floes of spring, and scattered by every summer storm, but after every shift they set- tle again at lower levels. Always they are advancing and filling the lake basin. The filling may seem slow and insignificant on the shore of one of the Great Lakes but its progress is obvious in a mill pond, and the dif-. ference is only relative. Fic. 12. An eroding bluff on the shore of Lake Michigan that is receding at the rate of several feet each year. The broad shelving beach in the fore- ground is sand, where the waves ordinarily play. Against the bare rising boulder-strewn strip back of this, the waves beat in storms; at its summit they gather the earth-slides from the bank above and carry them out into the lake. The black strip at the rear of the sand is a line of insect drift, deposited at the close of a midsummer storm by the turning of the wind on shore. On the other hand, lakes disappear with the cutting down of the rim of their basins in outflow channels. The Niagara river, for example, is cutting through the lime- 62 Types of Aquatic Environment stone barrier that retains Lake Erie. At Niagara Falls it is making progress at the rate of about five feet a year. Since the glacial period it has cut back from the shore of Lake Ontario a distance of some seventeen miles, and if the process continues it will in time empty Lake Erie. Fic.13. Evans’ Lake, Michigan; a lake in process of being filled by encroach- ment of plants. A line of swamp loose-strife (Decodon) leads the invading shore vegetation. Further inwash of silt or lowering of outlet is precluded by density of the surrounding heath. The plants control its fate. Photo by E. McDonald. When the glacier lay across the St. Lawrence valley, before it had retreated to the northward, all the waters of the great lakes region found their way to the ocean through the Mohawk Valley and the Hudson. At that time a similar process of cutting an outlet through a limestone barrier was going on near the site of the present village of Jamesville, New York, where on the The Great Lakes 63 Clark Reservation one may see today a series of abandoned cataracts, dry rock channels and plunge basins. Green Lake at present occupies one of these old plunge basins, its waters, perhaps a hundred feet deep, are surrounded on all sides but one, by sheer limestone cliffs nearly two hundred feet high. When lakes become populated then the plants and animals living in the water and about the shore line contribute their remains to the final filling of the basin. This is well shown in figure 13. The Great Lakes con- stitute the most magnifi- cent system of reservoirs of fresh water in the world; five vast inland seas, whose shores have all the sweep and majesty of the ocean, no land being visi- ble across them. All but one (Erie) have the bot- tom of their basins below the sea level. Their area, elevation and depth are as follows: Fic. 14. The larger lakes and rivers of North America. Areain Surface Depth in feet sq.mi. alt.inft. meant maximum Lake Ontario .... .... .. 7.240 247 300 738 tO SSHETIGS cevceeaviene siete itso 9.960 573 70 210 “ “Huron*® 22.5% 6oee% 23.800 581 250 730 “Michigan ..... ...... 22.450 581 325 870 “ Superior .... ..... 31.200 602 475 1.008 *Including Georgian Bay. tApproximate. They are stated by Russell to contain enough water to keep a Niagara full-flowing for a hundred years. 64 Types of Aquatic Environment The Finger Lakes of the Seneca basin in Central New York constitute an unique series occupying one section of the drainage area of Lake Ontario, with which they communicate by the Seneca and Oswego rivers. They occupy deep and narrow valleys in an upland plateau of soft Devonian shales. Their shores are rocky and increasingly precipitous near their southern ends. The marks of glaciation are over all of them. Keuka, the most picturesque of the series, occupies a forking valley partially surrounding a magnificent ice-worn hill. The others are all long and narrow and evenly contoured, without islands (save for a single rocky islet near the east Cayuga shore) or bays. The basins of these lakes invade the high hills to the southward, reaching almost to the head-waters of the tributaries of the Susquehanna River. Here there is found a wonderful diversity of aquatic situa- tion. At the head of Cayuga Lake, for example, beyond the deep water there is a mile of broad shelving silt-covered lake bottom, ending in a barrier reef. Then there is a broad flood plain, traversed by deep slow meandering streams, and covered in part by marshes. Then come the hills, intersected by narrow post-glacial gorges, down which dash clear streams in numerous beautiful waterfalls and rapids. Back of the first rise of the hills the streams descend more slowly, gliding along over pebbly beds in shining riffles, or loitering in leaf-strewn woodland pools. A few miles farther inland they find their sources in alder-bordered brooks flowing from sphagnum bogs and upland swales and springs. Thus the waters that feed the Finger Lakes are all derived from sources that yield little aquatic life, and they run a short and rapid course among the hills, with little time for increase by breeding: hence they contribute little to the population of the The Finger Lakes 65 lake. They bring in constantly, however, a supply of food materials, dissolved from the soils of the hills. Bordering the Finger marshes, save at the ends of Cayuga, and the chief irregularities of outline are formed by the deltas of inflowing streams. The two large central lakes, Cayuga and Sen- eca, have their basins extending below the sea level. Their sides are bordered by two steeply- rising, smoothly eroded hills of uniform height, between which they lie extended like wide placid rivers. The areas, eleva- tions and depths of the five are as follows: “cc “ Keuka Lakes there no extensive Fic. 15. The finger-lakes of Central New York. A, Canandaigua; B, Keuka; C, Seneca; D, Cayuga; E, Owasco; F, Skaneateles; G, Otisco; H, theSeneca River; I, The arrow indicates the location of the Cornell University Biological Field Station at Ithaca. The stippled area at the opposite end of Cayuga Lake marks the location of the Montezuma Marshes. Area Surface Depth in feet sq. mi. alt.inft. mean maximum 13.9 867 142 207 10.3 710 95 177 66.4 381 177, 435 67.7 444 288 618 18.1 709 99 183 16.3 686 126 274 Birge and Juday found the transparency of four of these lakes as measured by Secchi’s disc in August, 1910, to be as follows: Canandaigua Cayuga 12.0 ft. 16.6 ft. SENECA dinette alee aac 27.0 ft. Skaneateles 66 Types of Aquatic Environment The Lakes of the Yahara Valley in Southern Wisconsin They occupy broad, shallow basins formed by the deposition of barriers of glacial drift are of another type. Lake Kegonsa “e “cs ac Wabesa Monona Mendota in the preglacial course of the Yahara River. Their outlet is through Rock River into the Missis- sippi. Their shores are indented with numerous bays, and bordered ex- tensively by marshes. The surrounding plain is dotted with low rounded hills, some of which rise abruptly from the water, making attractive shores. The city of Madison is the location of the Uni- versity of Wisconsin, which Professor Birge has made the center of the most extensive and care- ful study of lakes yet undertaken in America. The area, elevation and depth of these lakes is as follows: Fic. 16. The four-lake region of Madison, Wisconsin. Areain Surface Depth in feet sq. mi. alt. in ft. mean maximum I5 842 15 31 3 844 15 36 6 845 27 75 15 849 40 85 Floodplain Lakes 67 Lakes resulting from Erosion—Although erosion tends generally to destroy lakes by eliminating their basins, here and there it tends to foster other lakes by making basins for them. Such lakes, however, are shallow and fluctuating. They are of two very different sorts, floodplain lakes and solution lakes. Floodplain Lakes and Ponds—Basins are formed in the floodplains of rivers by the deposition of barriers of eroded silt, in three different ways. 1. By the deposition across the channel of some large stream of the detritus from a heavily silt-laden tributary stream. This blocks the larger stream as with a partial dam, creating a lake that is obviously but a dilatation of the larger stream. Such is Lake Pepin in the Mississippi River, created by the barrier that is de- posited by the Chippewa River at its mouth. 2. By the partial filling up of the abandoned chan- nels of rivers where they meander through broad alluvial bottom-lands. Phelps Lake partly shown in the figure on page 50 is an example of a lake so formed; and all the other lakes of that figure are partly occluded by similar deposits of river silt. Horseshoe bends are common in slow streams, and frequently ariver will cut across a bend, shortening its course and opening a new channel; the filling up with silt of the ends of the abandoned channel results in the formation of an “‘ox- bow” lake; such lakes are common along the lower course of the Mississippi, as one may see by consult- ing any good atlas. . By the deposition in times of high floods of the bulk of its load of detritus at the very end of its course, where it spreads out in the form of a delta. Thus a barrier is often formed on one or both sides, encircling a broad shallow basin. Such is Lake Pontchartrain at the left of the ever extending delta of the Mississippi. 68 Types of Aquatic Environment Solution Lakes and Ponds—Of very different charac- ter are the lakes whose basins are produced by the dissolution of limestone strata and the descent of the overlying soil in the form of a “‘sink.’’ This is erosion, not by mechanical means at first, but by solution. It occurs where beds of soluble strata lie above the permanent ground water level, and are themselves Ri overlaid by clay. Rain water 3 ae oo Fic. 17. Solution lakes of Leon County, Florida, falling through the air gathers carbon dioxide and becomes a solvent of limestone. Percolat- \J ing downward through the soil it " passes through the permeable carbonate, dissolving it and (after Sellards). carrying its substance in solution tate sie” Pe *Kesing £4 Lower levels, often flowing out water 10 fat view and ¢ includes three common genera Biz, in cells of Mougeotia; a, (fig. 41)—Spirogyra, Zygnema, and Mougeotia. The first of these being one of the most widely used of biological ‘‘types’’ is known to almost every laboratory student. Its long, green, unbranched, slippery filaments are easily recognized among all the other greenery of the water by their beautiful spirally-wound bands of chlorophyll. The other common genera have also distinctive chlorophyll arrangement. Zygnema has a pair of more or less star-shaped green masses in each cell, one on either side of the central nucleus. In Mougeotia the chlorophyll a, alittle more than two cells g Docidium baculum n Tetmemorus from a filament of G ygon h Docidi dulat o Euastrum didelta b Spirotenia 4 Closterium pronum p Euastrum verrucosum c¢ Mesotenium j Closterium rostratum q Micrasterias oscitans d Netrium k Closterium moniliferum ry Micrasterias americana; (for e Cylindrocystis 1 Closterium ehrenbergi a third species see page 53). Sf Penium m Pleurotentum s Cosmarium, face view, and outline as seen from the side 120 Aquatic Organisms is in a median longitudinal plate, which can rotate in the cell: it turns its thin edge upward to the sun, but lies broadside exposed to weak light. Spirogyra is the most abundant, especially in early spring where it isfound in the pools ere the ice has gone out. All, being unattached (save as they become entangled with rooted aquatics near shore), prefer quiet waters. Immense accumulations of their tangled filaments often occur on the shores of shallow lakes and ponds, and with. the advance of spring and subsidence of the water level, these are left stranded upon the shores. They chiefly compose the ‘‘blanket-moss’’ of the fishermen. They settle upon and smother the shore vegetation, and in their decay they sometimes give off bad odors. Some- times they are heaped in windrows on shelving beaches, and left to decay. We most commonly see them floating at the surface in clear, quiet, spring-fed waters in broad filmy masses of yellowish green color, which in the sunlight fairly teem with bubbles of liberated oxygen. These dense masses of filaments furnish a home and shelter for a number of small animals, notably Haliplid beetle larve and punkie larve among insects; and entanglement by them is a peril to the lives of others, notably certain Mayfly larve (Blasturus). The rather large filaments afford a solid support for hosts of lesser sessile alge; and their considerable accumulation of organic contents is preyed upon by many parasites. Their role is an important one in the economy of shoal waters, and its importance is due not alone to their power of rapid growth, but also to their staying qualities. They hold their own in all sorts of temporary waters by develop- ing protected reproductive cells known as zygospores, which are able to endure temporary drouth, or other untoward conditions. Zygospores are formed by the fusion of the contents of two similar cells (the process Siphon Algae 121 is known as conjugation, whence the group name) and the development of a protective wall about the result- ing reproductive body. This rests for a time like a seed, and on germinating, produces a new filament by the ordinary process of cell division. These filamentous forms share this reproductive process with the desmids, and despite the differences in external aspect it is a strong bond of affinity between the two groups. The siphon alge—This peculiar group of green alge contains a few forms of little economic con- sequence but of great botanical interest. The plant body grows out in long irregularly branch- ing filaments which, though containing many nuclei, lack cross par- titions. The filaments SiG qa. Tp Siphon Sige thus resemble long open Aa eo? Wiudhdo ey ovary. sp spenmary. tubes, whence the name siphon alge. There are two common genera Vau- cheria and Botrydium (fig. 42). Both are mud-lov- ing, and are found partly out of the water about as often as wholly immersed. Vaucheria develops long, crooked, extensively interlaced filaments which occur in dense mats that have suggested the name “‘green felt.” These felted masses are found floating in ponds, or lying on wet soil wherever there is light and a con- stantly moist atmosphere (as, for example, in green- houses, where commonly found on the soil in pots). Botrydium is very different and much smaller. It has an oval body with root-like branches growing out from the lower end to penetrate the mud. It grows on the bottom in shoal waters, and remains exposed on the 122 Aquatic Organisms mud after the water has receded, dotting the surface thickly, as with greenish beads of dew. The water net and its allies—The water net (Hydro- dictyon) wherever found, is sure to attract attention by its curious form. It is a cylindric sheet of lace-like tissue, composed of slender green cells that meet at Fic. 43. A rather irregular portion of a sheet of water net (Hydrodictyon) their ends, usually by threes, forming hexagonal meshes like bobbinet (fig. 43). Such colonies may be as broad as one’s hand, or microscopic, or of any intermediate size; for curiously enough, cell division and cell growth are segregated in time. New colonies are formed by repeated division of the contents of single The Water Nets 123 cells of the old colonies. A new complete miniature net is formed within a single cell; and after its escape from the old cell wall, it grows, not by further division, but by increase in size of its constituent cells. Water net is rather local and sporadic in occurrence, but it sometimes develops in quantities sufficient to fill the waters of pools and small ponds. Fic. 44. Pediastrum: Several species from the plancton of Cayuga Lake. Pediastrum is a closely related genus containing a number of beautiful species, some of which are common and widespread. The cells of a Pediastrum colony are arranged in a roundish flat disc, and those of the outer- most row are usually prolonged into radiating points. Several species are shown in figure 44. In the open- 124 Aquatic Organisms meshed species the inner cells can be seen to meet by threes about the openings, quite as in the water net; but the cells are less elongate and the openings smaller. Five of the seven specimens shown in the figure lack these openings altogether. New colonies are formed within single cells, as in Hydrodictyon. In our figure certain specimens show marginal cells containing developing colonies. One shows an empty cell wall from whence a new colony has escaped. Other green alge— We have now men- i tioned a few of the more strongly ae| 2 marked groups of the green alge. There - are other forms, so = numerous we may not even name them here, many of which are common and widely dispersed. aie We shall have space Gal) J to mention only a Fic. 45. Filamentous Green Alge. few of the more im- “dhnulste appearance at upper end of cell ¢ p ortant among them, al Conferva; d, Draparnaldia. (After and we trust that the accompanying figures will aid in their recognition. Numerous and varied as they are, we will dismiss them from further consideration under a few arbitrary form types. 1. Simple filamentous forms. Of such sort are Ulothrix, CEdogonium, Conferva, etc., (fig. 45). Ulo- thrix is common in sunny rivulets and pools, especially in early spring, where its slender filaments form masses Other Green Algae 125 half floating in the water. The cells are short, often no longer than wide, and each contains a single sheet of Fic. 46. A spray of Cladophora, as it appears when outspread in the water, slightly magnified. chlorophyl, lining nearly all of its lateral wall. Ctdogo- nium is a form with stouter filaments composed of much longer cells, within which the chlorophyl is dis- 126 Aquatic Organisms posed in anastomosing bands. The thick cell walls, some of which show a peculiar cross striation near one end of the cell, are ready means of recognition of the members of this great genus. The filaments are attached when young, but break away and float freely in masses in quiet waters when older; it is thus they are usually seen. Conferva (Tribonema) abounds in shallow pools, especially in spring time. Its filaments are composed of elongate cells containing a number of separate disc-like chlor- | ophyl bodies. The cell wall is thicker toward the ends of the cell, and the filaments tend to break across the middle, forming pieces (halves of two adjacent cells) which appear distinctly H- shaped in optic section. This is a useful mark mu) fortheir recognition. It B) will be observed that these then are similar ’ in form and habits to ae eee cea. the filamentous conju- spherical colonies of C. pisiformis and gates discussed above, Cee SOE up they have not the peculiar form of chlor- ophyl bodies characteristic of that group. CEodgonium is remarkable for its mode of reproduction. 2. Branching filamentous forms—Of such sort are a number of tufted sessile alge of great importance: Cladophora, which luxuriates in the dashing waterfall, which clothes every wave-swept boulder and pier with delicate fringes of green, which lays prostrate its pliant sprays (fig. 46) before each on-rushing wave, and lifts Other Green Algae 127 them again uninjured, after the force of the flood is spent. And Chetophora (fig. 47; also fig. 89 on p. 182); which is always deeply buried under a transparent mass Fic. 48. Chztophora (either species) crushed and outspread in its own gelatinous covering and magnified to show the form of the filaments. of gelatin; which form little hemispherical hillocks of filaments in some species, and in one, extends outward in long picturesque sprays, but which has in all much the same form of plant body (fig. 48)—a close-set branch- ing filament, with the tips of some of the branches ending in a long hyaline bristle-like point. Chatophora grows very abundantly in stagnant pools, and ponds in mid- 128 Aquatic Organisms summer, adhering to every solid support that offers, and it is an important part of the summer food of many of the lesser herbivores in such waters. Then we must not omit to mention two that, if less important, are certainly no less interesting: Drapar- naldia (fig. 45d) which lets its exceedingly delicate sprays trail like tresses among the submerged stones in spring- Fic. 49. Coleochete scutata. ‘‘Green doily.” fed rivulets; and Coleochete (fig. 49), which spreads its flattened branches out in one plane, joined by their edges, forming a disc, that is oftenest found attached to the vertical stem of some reed or bulrush. Miscellaneous lesser green alge—Among other green alge, which are very numerous, we have space here for a mere mention of a few of the forms most likely to be met with, especially by one using a plancton net in open waters. These will also illustrate something of the Lesser Green Algae 129 remarkable diversity of form and of cell grouping among the lesser green alge. — _ Botryococcus grows in free floating single or compound clusters of little globose green cells, held together in a scanty gelatinous investment. The clusters are suffi- ciently grape-like to have suggested the scientific name. They.contain, when grown, usually 16 or 32 cells each. They are found in the open waters of bog pools, lakes, i Se 4 ; ego >, ac Sree Tee fl VY .83es Fic. 50. Miscellaneous green algee (mostly after West). a, Botryococcus; b, Celastrum; c, Dictospherium; d, Kirchnerella; e, Selenastrum; f, Ankistrodesmus falcatus; g, Ophiocytium; h, Tetraspora; %, Crucigenia; j, Scenedesmus;, k, Rhicteriella; 1, | ,. Ankistrodesmus setigerus; m, Oocystis. and streams, during the warmer part of the season,, being most abundant during the hot days of August. When over-abundant the cells sometimes become filled with a brick-red oil. They occur sparingly in water- bloom. i : a 8S Dictyospherum likewise grows in more or less spheri- cal colonies of globose cells. The cells are connected together by dichotomously branching threads and all are enveloped in a thin spherical mass of mucus. The colonies are free floating and are taken in the plancton of ponds and lakes and often occur in the water-bloom. - 130 Aquatic Organisms Celastrum is another midsummer plancton alga that forms spherical colonies of from 8 to 32 cells, it has much firmer and thicker cell walls, and the cells are often angulate or polyhedral. New colonies are formed within the walls of each of the cells of the parent colony, and when well grown these escape by rupture or dissolution of the old cell wall. Our figure shows merely the out- line of the cell walls of a 16-celled colony, in a species having angulate cells, between which are open inter- spaces. Kofoid found Coelastrum occurring in a maxi- mum of 10,800,000 per cubic meter of water in the Illinois River in August. Crucigenia is an allied form having ovoid or globose cells arranged in a flat plate held together by a thin mucilaginous envelope. The cells are grouped in fours, but 8, 16, 32, 64 or even more may, when undisturbed, remain together in a single flat colony. During the warmer part of the season, they are common constit- uents of the fresh-water plancton, the maximum heat of midsummer apparently being most favorable to their development. Scenedesmus is a very hardy, minute, green alga of wide distribution. There is hardly any alga that appears more commonly in jars of water left standing about the laboratory. When the sides of the jar begin to show a film of light yellowish-green, Scenedesmus may be looked for. The cells are more or less spindle- shaped, sharply pointed, or even bristle-tipped at the ends. They are arranged side by side in loose flat rafts of 2, 4 or 8 (oftenest, when not broken asunder, of 4) cells. They are common in plancton generally, espec- ially in the plancton of stagnant water and in that of polluted streams, and although present at all seasons, they are far more abundant in mid and late summer. Lesser Green Algae 131 Kirchnerella is a loose aggregate of a few blunt- pointed U-shaped cells, enveloped in a thick spherical mass of jelly. It is met with commonly in the plancton of larger lakes. Selenastrum grows in nearly naked clusters of more crescentic, more pointed cells which are found amid shore vegetation. Ankistrodesmus is a related, more slender, less crescentic form of more extensive littoral distribution. The slenderest form of this genus are free floating, and some of them like A. setigera fig. 501 are met with only in the plancton. Richteriella is another plancton alga found in free floating masses of a few loosely aggregated cells. The cells are globose and each bears a few long bristles upon its outer face. Kofoid found Richteriella attaining a maximum of 36,000,000 per cubic meter of water in September, while disappearing entirely at temperatures below 60° F. Oocystis grows amid shore vegetation, or the lighter species, in plancton in open water. The ellipsoid cells exist singly, or a few are loosely associated together in a clump of mucus. The cells possess a firm smooth wall which commonly shows a nodular thickening at each pole. Ophiocytium is a curious form with spirally coiled multinucleate cells. The bluntly rounded ends of the cells are sometimes spine-tipped. These cells some- times float free, sometimes are attached singly, some- times in colonies. Kofoid found them of variable occurrence in the Illinois River, where the maximum number noted was 57,000,000, per cubic meter occur- ring in September. The optimum temperature, as attested by the numbers developing, appeared to be about 60° F. Tetraspora—We will conclude this list of miscellanies with citing one that grows in thick convoluted strings 132 Aquatic Organisms and loose ropy masses of gelatin of considerable size. These masses are often large enough to be recognized with the unaided eye as they lie outspread or hang down. upon trash on the shores of shoal and stagnant waters.. Within the gelatin are minute spherical bright green cells, scattered or arranged in groups of fours. BLUE-GREEN ALG& (Cyanophycee or Myxophycee). The “‘blue-greens”’ are mainly freshwater alge, of simple forms. The cells exist singly, or embedded together in loose gelatinous envelope or adhere in flat rafts or in filaments. Their chlorophyll is rather uniformly dis- tributed over the outer part of the cell (quite lacking the restriction to specialized chloroplasts seen in the true’ green-alge) and its color is much modified by the presence of pigment (phycocyanin), which gives to the cell usually a pronounced bluish-green, sometimes, a reddish color. Blue-green algze exist wherever there is even a little transient moisture—on tree trunks, on the soil, in lichens, etc.; and in all fresh water they play an import- ant role, for they are fitted to all sorts of aquatic situations, and they are possessed of enormous reproduc- tive capacity. Among the most abundant plants in the water world are the Anabenas (fig. 00), and other blue- greens that multiply and fill the waters of our lakes in midsummer, and break in ‘“‘water-bloom”’ covering the entire surface and drifting with high winds in windrows on shore. Such forms by their decay often give to the water of reservoirs disagreeable odors and bad flavors, and so they are counted noxious to water supplies. There are many common blue-greens, and. here we have space to mention but a few of the more common forms. Two of the loosely colonial forms composed of spherical cells held together in masses of mucus are Celospherium and Microcystis. Both these are: often Tetranspora . 133 associated with Anabzena in the water-bloom. Ccelos- pheerium is a spherical hollow colony of microscopic size. It is a loose association of cells, any of which on separa- tion is capable of dividing and producing a new colony. Microcystis (fig. 514A) isa mass of smaller cells, a very loose colony that is at first more or less spherical but later becomes irregularly lobed and branching. Such old colonies are often large enough to be observed with the naked eye. They are found most commonly inlate summer, being hot weather forms. When abundant these two are often tossed by the waves upon rocks along the water’s edge, and from them the dirty blue- green deposit that is popularly known as “oreen paint.” Among the members Fic. 51. Miscellaneous blue-green of this group most com- . ae arta hts bie _, monlyseenarethemotile A tcrocystis (Clathrocystis); B, C, D, Purapele: 3. spesiines ¥. Nose ¢, Dlue-greens of the genus Oscillatoria (fig. 51G). These grow in dense, strongly colored tufts and patches of exceedingly slender filaments attached to the bottoms and sides of watering troughs, ditches and pools, and on the beds of ponds however stagnant. They thickly cover patches of the black mud bottom and the formation of gases beneath them disrupts their attachment and the broken flakes of bottom slime that they hold together, rise to the surface and float there, much to the hurt of the appearance of the water. The filaments of Oscillatoria and of a few of its near allies perform curious oscillating and gliding movements. Detached filaments float freely in the open water, and 134 Aquatic Organisms during the warmer portion of the year, are among the commoner constituents of the plancton. There are a number of filamentous blue-greens that are more permanently sessile, and whose colonies of filaments assume more definite form. Rivularia is typical of these. Rivularia grows in hemispherical gelatinous lumps, attached to the leaves and stems of submerged seed plants. In autumn it often fairly smothers the beds of hornwort (Ceratophyllum) and water fern (Marsilea) in rich shoals. Rivularia is Fic. 52. Colonies of Rivularia on a disintegrating Typha leaf. brownish in color, appearing dirty yellowish under the microscope. Its tapering filaments are closely massed together in the center of the rather solid gelatinous lump. The differentiation of cells in the single filament is shown in fig. 51H. Such filaments are placed side by side, their basal heterocysts close together, their tips diverging. As the mass grows toa size larger than a pea it becomes softer in consistency, more loosely attached to its support and hollow. Strikingly different in form and habits is the raftlike Merismopedia (fig. 53). It is a flat colony of shining blue-green cells that divide in two planes at right angles to each other, with striking Red and Brown Algae 135 regularity. These rafts of cells drift about freely in open water, and are often taken in the plancton, though rarely in great abundance. They settle betimes on the leaves of the larger water plants, and may be discovered with a pocket lens by searching the sediment shaken therefrom. Fic. 53. Merismopeedia. REpD and BROWN ALG (Rhodophycee and Pheophycee) —These groups are almost exclusively marine. A few scattering forms that grow in fresh water are shown in figure 54. Lemanea is a torrent-inhabiting form that grows in blackish green tufts of slender filaments, attached to the rocks in deep clear mountain streams where the force of the water is greatest. It is easily 136 Aquatic Organisms recognizable by the swollen or nodulose appearance of the ultimate (fruiting) branches. Chantransia is a beautiful purplish-brown, extensively branching form that is more widely distributed. It is common in clear flowingstreams. Itmuch resembles Cladophorain man- ner of growth but is at once distinguished by its color. Fic. 54. Red and brown alge (after West). u, Lemanea; b, Chantransia; c, Batrachospermum; d, Hydrurus. Batrachospermum is a freshwater form of wide distri- bution, with a preference for spring brooks, though occur- ring in any water that is not stagnant. It grows in branching filaments often several inches long, enveloped in a thick coat of soft transparent mucus. The color is bluish or yellowish-green, dirty yellow or brownish. Attached to some stick or stone in a rivulet its sprays, of more than frond-like delicacy, float freely in the water. . .Hydrurus grows in branched colonies embedded in a tough mucilage, attached to rocks in cold mountain streams. The colonies are often several inches long. Their color is olive green. They have a plumose appearance, and are of very graceful outline. The Stoneworts 137 The stoneworts (Characee).—This group is well repre- sented in freshwater by two common genera, well known to every biological: laboratory student, Chara and Nitella. Both grow ‘in protected shoals, and in the borders.of clear lakes at depths below the heavy beating of the waves. Both are brittle and cannot withstand Fic, 55. Nitella glomerulifera. wave action. Both prefer the waters that flow off from calcareous soils, and are oftenest found attached to a stony bottom. | : _ The stoneworts, are the most specialized of the fresh- water alge: indeed, they are not ranked as alge by some botanists. In form they have more likeness to certain land plants than to any of the other alge. 138 _ Aquatic Organisms They grow attached to the soil. They grow to consider- able size, often a foot or more in length of stem. They grow by apical buds, and they send out branches in regular whorls, which branch and branch again, giving the plant as a whole a bushy form. The perfect regu- larity of the whorled branches and the brilliant colora- tion of the little spermaries borne thereon, doubtless have suggested the German name for them of ‘‘Cande- labra plants.”’ The stoneworts are so unique in structure and in repro- ductive parts that they are easily distinguished from other plants. The stems are made up of nodes and internodes. The nodes are made up of short cells from which the branches arise. The internodes are made up of long cells (sometimes an inch or more long), the central one of which reaches from one node to another. In Nitella there is a single naked internodal cell com- posing entirely that portion of the stem. In Chara this axial cell is covered externally by a single layer of slenderer cortical cells wound spirally about the central one. Aglance with a pocket lens will determine whether there is a cortical layer covering the axial internodal cell, and so will distinguish Chara from Nitella. Chara is usually much more heavily incrusted with lime in our commoner species, and in one very common one, Chara fetida, exhales a bad odor of sulphurous compounds. The sex organs are borne at the bases of branchlets. There is a single egg in each ovary, charged with a rich store of food products, and covered by a spirally wound cortical layer of protecting cells. These, when the egg is fertilized form a hard shell which, like the coats of a seed, resist unfavorable influences for a long time. This fruit ripens and falls from the stem. It drifts about over the bottom, and later it germinates. At the apex of the ovary is a little crown of cells, between which lies the passageway for the entrance of Colorphylless Plants 139 the sperm cell at the time of fertilization. This crown is composed of five cells in Chara; of ten cells in Nitella. It is deciduous in Chara; it is persistent in Nitella. The stoneworts, unlike many other alge, are wonder- fully constant in their localities and distribution, and regular in their season of fruiting. They cover the same hard bottoms with the same sort of gray-green meadows, year after year, and although little eaten by aquatic animals, they contribute important shelter for them, and they furnish admirable support for many lesser epiphytes. CHLOROPHYLLESS WATER PLANTS, BACTERIA AND FUNGI Nature’s great agencies for the dissolution of dead organic materials, in water as on land, are the plants that lack chlorophyl. They mostly reproduce by means of spores that are excessively minute and abund- ant, and that are distributed by wind or water every- where; consequently they are the most ubiquitous of organisms. They consume oxygen and give off carbon dioxide as do the animals, and having no means of obtaining carbon from the air, must get it from car- bonaceous organic products—usually from some carbo- hydrate, like sugar, starch, or cellulose. Some of them can utilize the nitrogen supply of the atmosphere but most of them must get nitrogen also from the decompo- sition products of pre-existing proteins. Many of them produce active ferments, which expedite enormously the dissolution of the bodies of dead plants and animals. Some bacteria live without free oxygen. It follows from the nature of their foods, that we find these chlorophylless plants abounding where there is the best supply of organic food stuffs. Stagnant pools filled with organic remains, and sewers laden with the (I40 Aquatic Organisms city’s waste. But there is no natural water free from them. Leta dead fly fall upon the surface of a tumbler of pond water and remain there for a day or two and it becomes white with water mold, whose spores were present in the water. Let any organic solution stand exposed and quickly the evidence of rapid decomposition appears init. Even the dilute solutions contained in a laboratory aquarium, holding no organic material other than a few dead leaves will often times acquire a faint purple or roseate hue as chromogenic bacteria multiply in them. Bacteria—A handful of hay in water will in a few hours make an infusion, on the surface of which a film of ‘bacterial jelly”’ will gather. If a bit of this ‘‘jelly” be mounted for the microscope, the bacteria that secrete it may be found immersed in it, and other bacteria will be found adherent to it. All the common form- types, bacillus, coccus and spirillum are likely to be seen readily. Thus easy is it to encourage a rich growth of water bacteria. Among the bacteria of the water are numerous species that remain there constantly (often called ‘natural water bacteria’), commingled at certain times and places with other bacteria washed in from the surface of the soil, or poured in with sewage. From the last named source come the species injurious to human health. These survive in the open water for but a short time. The natural water bacteria are mainly beneficial; they assist in keeping the world’s food supply in circula- tion. Certain of them begin the work of altering the complex organic substances. They attack the proteins and produce from them ammonia and various ammonia- cal compounds. Then other bacteria, the so-called “nitrifying’’ bacteria attack the ammonia, changing it to simpler compounds. Two kinds of bacteria succes- sively participate in this: one kind oxidizes the . Bacteria 141 ammonia to nitrites; a second kind oxidizes the nitrites to nitrates. By these successive operations the stores of nitrogen that are gathered together within the living bodies of plants and animals are again released: for further use. The simple nitrates are proper food for the green alge, with whose growth the cycle begins again. And those bacteria which promote the pro- cesses of putrefaction, are thus the world’s chief agen- cies for maintaining undiminished growth in perpetual successio Bacteria are among the smallest of organisms. Little of bodily structure is discoverable in them even with high powers of the microscope, and consequently they are studied almost entirely in specially prepared cul- tures, made by methods that require the technical training of the bacteriological laboratory for their mastery. Any one can find bacteria in the water, but only a trained specialist can tell what sort of bacteria he has found; whether pathogenic species like the typhoid bacillus, or the cholera spirillum; or whether harmless species, normal to pure water. The higher bacteria—Allied to those bacilli that grow in filaments are some forms of larger growth, known as Trichobacteria, whose filaments sometimes grow attached in colonies, and in some are free and motile. A few of those that are of interest and importance in fresh-water will be briefly mentioned and illustrated here. Leptothrix* (Fig. 56a, b and c) grows in tufts of slender, hairlike filaments composed of cylindric cells sur- rounded by a thin gelatinous sheath. In reproduction the cells are transformed directly into spores (gonidia) which escape from the end of the sheath and, finding favoring conditions, grow up into new filaments. *Known also as Streptothrix and Chlamydothrix. ub 142 Aquatic Organisms Crenothrix (Fig. 56 d, e and f) is a similar unbranched sessile form which is distinguished by a widening of the filaments toward the free end. This is caused by a division of the cells in two or three planes within the sheath of the filament, previous to spore formation. Often by the germination of spores that have settled upon the outside of the old sheaths and growth of new filaments therefrom compound masses of appreciable Fic. 56. Trichobacteria. u, b, c, Leptothrix (Streptothrix, or Chlamydothrix). a,acolony; b, a single filament; c, spore formation; d, e, f, Crenothrix; d, a single growing filament; e¢, a fruiting filament; f, a compound colony; g, Cladothrix, a branching filament; h, Beggiatoa, younger and older filaments, the latter showing sulphur granules, and no septa between cells of the filament. size are produced. In the sheaths of the filaments a hydroxide of iron is deposited (for Crenothrix possesses the power of oxidizing certain forms of iron); and with continued growth the deposits sometimes become sufficient to make trouble in city water supply systems by stoppage of the pipes. In nature, also, certain deposits of iron are due to this and allied forms properly known as iron bacteria. Cladothrix (Fig. 56 g), is a related form that exhibits a peculiar type of branching in its slender cylindric filaments. Water Molds 143 Beggiatoa (fig. 56 h) is the commonest of the so-called sulfur bacteria. Its cylindric unbranched and unat- tached filaments are motile, and rotate on the long axis with swinging of the free ends. The boundaries be- tween the short cylindric cells are often obscure, especially when (as is often the case) the cells are filled with highly refractive granules of sulfur. Considerable deposits of sulfur, especially about springs, are due to the activities of this and allied forms. Water molds—True fungi of a larger growth abound in all fresh waters, feeding on almost every sort of organic substance contained therein. The commonest of the water molds are the Sap- rolegnias, that so quickly overgrow any bit of dead animal tissue which may chance to fall upon the sur- |’ face of the water and float there. If it be a fly, in a day or two its body is sur- rounded by a white fringe of } radiating fungus filaments, : Fic. 57. A common water mold, outgrowing from the body. Saprolegnia. (After Engler and The tips of many of these Prantl.) _ ; filaments terminate in cylin- “ *6f'R% Siycelhim' that pencérates the dric sporangia, which when swank spores ie "Ps with escap- mature, liberate from their ruptured tips innumerable biciliated free-swimming swarm spores. These wander in search of new floating carcases, or other suitable food. Certain of these water molds attack living fishes, entering their skin wherever there is a a slight abrasion of the surface, and rapidly producing diseased condi- tions. These are among the worst pests with which the fish culturist has to contend. They attack also the 144 Aquatic Organisms eggs ‘ fishes during their incubation (see. fig: 00 on p. 00). Most water molds live upon other plants. Even the Saprolegnias have their own lesser mold parasites: Many living alge, even the lesser forms like desmids and diatoms are subject to their attack. Fine cultures of such alge are sometimes run through with an epidemic of mould parasites and ruined. THE HIGHER PLANTS (Mossworts, Fernworts and Seed Plants) In striking contrast with the alge, the higher plants live mainly on land, and the aquatics among them are restricted in distribution to shoal waters and to the vicinity of shores. There is much in the bodily organization of nearly all of them that indicates ancestral adaptation to life on land. They have moreofhard parts, more of localized feeding organs, more of epidermal specialization, and more dif- erentiation of parts in the body, than life in the water demands. They occupy merely the margins of thewater. Afew highly specialized genera, well equipped for with- standing partial or complete submergence occupy the shoals and these are backed are 58. The marsh mallow, On Rhea cetera line by = tbiscus Moscheutos. mingled lot of semi-aquatics that are for the most part but stray members of groups that abound on land. Often they are single members of large groups and are sufficiently distinguished from their fellows by a name indicating the kind of wet place in which they grow. Thus we know familiarly the floating riccia, the bog mosses, the brook speedwell, the water fern and water cress, the marsh bell flower and the marsh fern, the swamp horsetail and the swamp iris, etc. All these 145 146 Aquatic Organisms and many others are stragglers from large dry land groups. That readaptation to aquatic life has occurred many times independently is indicated by the fact that the more truly aquatic families are small and highly specialized, and are widely separated systematically. Bryophytes—Both liverworts and mosses are found in our inland waters, though the former are but spar- ingly represented. Two simple Riccias, half an inch long when grown, are the liverworts most commonly found. One, Riccia fluitans, grows in loose clusters of flat slender forking sprays that drift about so freely that fragments are often taken in pond and river plancton. The larger unbroken more orless spherical masses of sprays arefound rolling with the waves upon the shores of muddy ponds. The other, Ricciocarpus natans, has larger and thicker sprays of green and purple hue, that float singly upon the surface, or gather in floating masses covering considerable areas of quiet water. They are not uncommonly found in springtime about the edges of muddy ponds. Under- neath the flat plant body there is a dense brush of flattened scales. Water mosses are more important. The most remarkable of these are the bog mosses (Sphagnum). These cover large areas of the earth’s surface, especially in northern regions, where they chiefly compose the thick soft carpet of vegetation that overspreads open bogs and coniferous swamps. They are of a light grey- green color, often red or pink at the tips. These mosses do not grow submerged, but they hold immense quantities of water in their reservoir cells, and are able to absorb water readily from a moist atmosphere; so they are always wet. Supported on a framework of entangled rootstocks of other higher plants, the bog mosses extend out over the edges of ponds in floating mats, which sink under one’s weight beneath the water Mossworts . 147 level and rise again when the weight is removed. The part of the mat which the sphagnum composes consists of erect, closely-placed, unbranched stems, like those shown in fig. 59, which grow ever upward at their tips, Fic. 59. Bog-moss, Sphagnum. and die at the lower ends, contributing their remains to the formation of beds of peat. The leaves of Sphagnum are composed of a single layer of cells that are of two very different sorts. There are numerous ordinary narrow chlorophyl-bearing cells, and, lying between these, there are larger perforate reservoir cells, for holding water. 148 Aquatic Organisms The true water mosses of the genus Fontinalis are fine aquatic bryophytes. These are easily recognized, being very dark in color and very slender. They grow in spring brooks and in clear streams, and are often seen in great dark masses trailing their wiry stems where the current rushes between great boulders or leaps into foam-flecked pools in mountain brooks. Another slender brook-inhabiting moss is Fissidens julianum, which somewhat resembles Fontinalis, but which is at once distinguished by the deeply channeled bases of its leaves, which enfold the stem. The leaves are two ranked and alternate along the very slender flexuous stem, and appear tobe set with edges toward it. There are also a few lesser water mosses allied () to the familiar trailing hypnums, so common in deep woods. They grow Fic. 60. Water mosses. on stones in the bed of a, Fontinalis; b, Fissidens julianum, with a brooks. They cover the single detached leaf, more enlarged; c, Achy ACh segH ne rusciforme, with a single face of the ledges over tached leaf at the left. (After Grout.) e ‘ which the water pours in floods and trickles in times of drouth, as with a fine feathery carpet of verdure that adds much to the beauty of the little waterfalls. They give shelter in such places to an interesting population of amphibious animals, as will be noted in chapter VI, following. The leaves of the hypnums are rather short and broad, and in color they are often very dark—often almost black.* *Grout has given a few hints for the recognition of these ‘“Water-loving hypnums” in his Mosses with a Hand Lens, 2d edition, p. 128. New York, 1905. Peteridophytes 149 There are also a few hypnums found intermixed with sphagnum on the surface of bogs, and as everyone knows there are hosts of mosses in all moist places in woods and by watersides. Fic. 61. Two floating leaves of the ‘water shamrock,” Marsilea, in the midst of a surface layer of duck-meat (Spirodela polyrhiza). Pteridophytes—Aquatic fernworts are few and of very unusual types. There are at least two of them, how- ever, that are locally dominant in our flora. Marsilea, the so-called water shamrock or water fern, abounds on 150 Aquatic Organisms the sunny shoals of muddy bayous about Ithaca and in many places in New England. It covers the zone between high and low water, creeping extensively over the banks that are mostly exposed, and there forming a most beautiful ground cover, while producing longer leaf-stalks where submerged. These leaf-stalks carry the beautiful four-parted leaf-blades to the surface where they float gracefully. Fruiting bodies the size Fic. 62. Floating plants: The largest branching colonies are Azolla; the smallest plants are Wolfia; those of intermediate size are Lemna minor. Photo by Dr. Emmeline Moore. of peas are produced in clusters on the creeping stems above the water line, often in very great abundance. Then there are two floating pteridophytes of much interest. Salvinia, introduced from Europe, is found locally along our northeastern coast, and in the waters of rich bottom lands south and westward the brilliant little Azolla flourishes. Azolla floats in sheltered bogs and back waters, intermingled with duckweeds. It is reddish in color oftener than green and grows in minute mosslike pinnately branched sprays, covered with Aquatic Seed Plants I5I closely overlapping two-lobed leaves, and emits a few rootlets from the under side which hang free in the water. Inthe back waters about the Illinois Station at Havana, Illinois, Azolla forms floating masses often several feet in diameter, of bright red rosettes. Shoreward there are numerous pteridophytes grow- ing as rooted and emergent aquatics; the almost grass- like Jsoetes, and the marsh horsetails and ferns, but these latter differ little from their near relatives that live on land. Aquatic Seed Plants—These are manifestly land plants in origin. They have much stiffening in their stems. They have a highly developed epidermal system, often retaining stomates, although these can be no longer of service for intake of air. They effect fertilization by means of sperm nuclei and pollen tubes, and not by free swimming sperm cells.’ Seed plants crowd the shore line, but they rapidly diminish in numbers in deepening water. They grow thickest by the waterside because of the abundance of air moisture and light there available. But too much moisture excludes the air and fewer of them are able to grow where the soil is always saturated. Still fewer grow in standing water and only a very few can grow wholly submerged. Moreover, it is only in protected shoals that aquatic seed plants flourish. They cannot. . withstand the beating of the waves on exposed shores. Their bodies are too highly organized, with too great’. differentiation of parts. Hence the vast expanses of open waters are left in possession of the more simply organized alge. An examination of any local flora, such as that of the Cayuga Lake Basin* will reveal at once how small a part of the population is adapted for living in water. *The following data are largely drawn from Dudley’s Cayuga Flora, 1886. 152 Aquatic Organisms In this area there are recorded as growing without cultivation 1278 species. Of these 392 grow in the water. However, fewer than forty species grow wholly submerged, with ten or a dozen additional submerged except for floating leaves. Hardly more than an eighth, therefore, of the so- called ‘“‘aquatics’’ are truly aquatic in mode of life: the remaining seven-eighths grow on shores and in springs, in swamps and bogs, in ditches, pools, etc., where only their roots are constantly wet. The aquatic seed plants are representa- tive of a few small and scattered families. In- deed, the only genus having any consider- yee able number of truly gga . aquatic species is the ee 4 _-—-*| naiad genus Potamo- geton. Other genera of river-weeds, or true pond weeds, are small Fic. 63. The ruffled pond-weed; Pota- scattered and highly mogeton crispus, one of the most orna- diversified. They bear mental of fresh water plants. many earmarks of independent adaptation to the special situations in the water which they severally occupy. In the economy of nature the Potamogetons or river weeds constitute the most important single group of sub- merged seed plants. They are rooted to the bottom in most shoal waters, and compose the greater part of ; l ea ai Aquatic Seed Plants 153 the larger water meadows within our flora. They have alternate leaves and slender flexuous stems that are often incrusted with lime. There are evergreen species among the Potamogetons, and other species that die down in late summer. There are broad leaved and narrow leaved species. There are a few, like the familiar P. natans whose uppermost leaves (see fig. 00 on page 00) float on the surface, but the more important members of the genus live wholly submerged. Tho seed-plants, they mainly reproduce vegetatively, by specialized reproductive buds that are developed in the growing season, and are equipped with stored starch and other food reserves, fitting them when detached for rapid growth in new situations. These reproductive parts are developed in some species as tuberous thickenings of underground parts (see figure 00 on page 00); in others as burr-like clusters of thick- ened apical buds; and in still others they are mere thickenings of detachable twigs. The Potamogetons enter largely into the diet of wild ducks and aquatic rodents and other lesser aquatic herbivores. They are as important for forage in the water as grasses are on land. Other naiads are Nats (fig. 85) and Zannichellia. Eel-grass (Vallisneria) is commonly mixed with the pond weeds in lake borders and water meadows. Eel-grass is apparently stemless and has long, flat, flexuous, translucent, ribbonlike leaves, by which it is easily recognized. The duckweeds (Lemnacez, figs. 61 and 62) are peculiar free-floating forms in which the plant body is a small flat thallus, that drifts about freely on the surface in sheltered coves, mingled with such liverworts as Ricciocarpus, with such fernworts as Azolla, with seeds, eel-grass flowers, and other flotsam. There are definite upper and lower surfaces to the thal- lus with pendant roots beneath hanging free in the 154 Aquatic Organisms water. lobes from pre-existing thalli. production are of rare occurrence. Increase is by budding and outgrowth of new A, and C, the hornwort (Ceratophyllum); B, the water milfoil A is an old leaf, the upper half normally covered with alge and silt; the lower half cleaned, save for a closely adherent dwelling-tube of a midge larva in the fork at C, is a young partly expanded leaf whorl from the (Myriophyllum). the right. apical bud. Fic. 64. Leaf-whorls. Flowering and seed The water lily family includes the more con- spicuous of the broad-leaved aquatics, which pre-empt the rich bottom mud with stout root stocks, and heavily shade the water with large shield- shaped leaves, either floating upon the sur- face, as in the water shield and water lilies or lifted somewhat aboveit, asin the spatterdock and the lotus. They are long-lived perennials, re- quiring a rich muck soil to root in. These are distinguished for the beauty and fragrance of their flowers. Aquatic Seed Plants 155 The bladderworts (Utricularia) comprise another peculiar group. They are free-floating, submerged plants with long, flexuous branching stems that are thickly clothed with dissected leaves. Attached to the leaves are the curious traps or “‘bladders’’ (discussed in Chapt. VI) which have suggested the group name. Being unattached they frequent the still waters of sheltered bays and ponds where they form beautiful feathery masses of green. They shoot up stalks above the surface bearing curious bilabiate flowers. Fic. 65. The water weed, Philotria (ladchards or Elodea), with two young black-and-green-banded nymphs of the dragonfly Anax on its stem, and a snail, Planorbis, on a leaf. The hornwort (Ceratophyllum) is another non-rooting water plant that grows wholly submerged and branch- ing. It is coarser, however, and hardier than Utricu- laria and much more widespread. Its leaves are stiff, repeatedly forking, and spinous-tipped (fig. 64 A and C). The water milfoils (Myriophyllum) are rooted aqua- tics, superficially similar to the hornwort but dis- tinguishable at a glance by the simple pinnate branch- ing of the softer leaves (fig. 64B). Then there are a few very common aquatics that form patches covering the beds of lesser ponds, bogs 156 Aquatic Organisms and pools. The common water weed, Philotria, (fig. 65), with its neat little leaves regularly arranged in whorls of threes; and two water crowfoots, Ranunculus, (fig. 66), white and yellow, with alternate finely dissected leaves; and the water purslane, Ludvigia palustris, with its closely-crowded opposite ovate leaves. These are the common plants of the waterbeds about Ithaca. They are so few one may learn them quickly, for so strongly marked are they that a single spray or often a single leaf is adequate for recognition. Then there are three small families so finely adapted to withstand- ing root submersion that they dominate all our permanent shoals and marshes. These are (1) the Typhaceze including the cat-tails and the bur-reeds, a Pee white water-crow- 1h form vaststretch- es of nearly clear growth, as discussed in the last chapter; (2) the Alis- mace, including arrow heads and water plantain, and (3) the Pontederiacez, represented by the beautiful blue pickerel-weed. All these are shown in their native haunts in the figures of chapter VI. Another family of restricted aquatic habitat is the Droseracez, the sun-dews, which grow in the borders of sphagnous upland bogs. They are minute purplish- tinted plants whose leaves bear glandular hairs. Few other families are represented in the water by more than a small proportion of their species. Those Aquatic Seed Plants 157 families are best represented whose members live chiefly on low grounds and in moist soil. A few rushes (Juncaceze) invade the water on wave-washed shores at fore front of the standing aquatics. A few sedges Fic. 67. Fruit clusters of four emergent aquatic seed plants; arrow-arum (Peltandra), pickerel-weed (Pon- tederia), burr-reed (Sparganium), and sweet flag (Acorus). (Carices) overrun flood-plains or fringe the borders of ditches. A very few grasses preémpt the beds of shallow and impermanent pools. A few aroids, such as arrow arum and the calla adorn the boggy shores. A few heaths, such as, Cassandra and Andromeda over- spread the surface of upland sphagnum bogs with dense 158 Aquatic Organisms levels of shrubs, and numerous orchids occupy the sur- face of the bog beneath and between the shrubs. Willows and alders fringe all the streams, associated there with a host of representatives of other families crowding down to the waterside. A few of these on account of their usefulness or their beauty, we shall have occasion to consider in a subsequent chapter. Such are the dominant aquatic seed plants in the Cayuga Basin; and very similar are they over the greater part of the earth. The semi-aquatic represen- tatives of the larger families are few and differ little from their terrestrial relatives: the truly aquatic families are small and highly diversified. ANIMALS ANY of the lower groups of animals are wholly aqua- tic, never having de- parted from their ances- tral abode. Other groups are in part adapted to life on land.