GIFT OF Professor W.A.Setohell BIOLOGY LIBRARY Compliment* of tbe Urgent* of tlje and of ttjc 3utt)or, Minnesota Plant Diseases. A Wound Parasite (Plettrotus ulmarius) on the Trunk of a Maple Tree* Original. MINNESOTA PLANT DISEASES by E. M. Freeman, Ph. D. Assistant Professor of Botany University of Minnesota Report of the Survey Botanical Series Saint Paul, Minnesota July 31 , i 905 A GIFT OF BIOLOGY ft" PUBLISHED BY AUTHORITY OF THE BOARD OF REGENTS OF THE UNIVERSITY FOR THE PEOPLE OF MINNESOTA Edition, 2,500 copies Preface* is probably safe to say that millions of dollars are lost in Minnesota yearly by the ravages of plant diseases. Agriculturists and horticulturists all over the world have of late years directed a great deal of attention toward the study of plant diseases and the methods of combating them. The Department of Agriculture of the United States has done vastly more than any other institution in the world along this line and the results have been well worth the efforts, for many efficient methods of fighting these pests have been devised. In many cases where cure is impossible an intelligent understanding of the con- ditions and effects of a disease will aid in prevention. The dissemination of such knowledge is of very great value. It is a very evident fact that all agricultural pur- suits are taking great strides, and the education of those boys and girls who are about to cultivate or manage the cultivation of lands is becoming more and more impera- tive. The possession of an accurate knowledge of plant diseases and their causes is not only of commercial use to the farmer, both in cure and prevention, but also, by making him an intelligent observer, adds hosts of assistants to the small corps of men who are devoting their time to this study of botanical science. The advantages of such a condition amongst agriculturists would far surpass those where the mere knowledge of present methods of prevention and cure obtains* In fact it is only with the intelligent and hearty co operation of farmers that such work can successfully go forward. It is not the aim of this work therefore to catalogue all of the ills that Minnesota plants are heir to, but its chief object is to disseminate knowledge of the destructive parasites of the useful plants of this state, to assist all concerned in the cultivation of plants to a more intelligent and thorough understanding of the habits of these para- sites, and to point out established methods of combating such diseases. Recipes are not the aim of such a work — these are of value and as such are introduced ; but by far the most valuable effort should be the inculcation of the knowledge of the habits and life-stories of those organisms which are the causes of disease. Upon such knowledge, widely disseminated, can be built a substantial system of disease preven- tion. In short, the aim of this work is rather educational than immediately practi- cal, for in the former feature the author hopes that it will be ultimately most useful. viii Minnesota Plant Diseases. It is to be regretted that a systematic survey of the plant diseases of the state , sufficiently thorough to determine the full extent of the damage due to these diseases, has not been possible. The Minnesota Agricultural Experiment Station has never employed a special plant pathologist, and the records of the station on plant diseases are therefore only fragmentary. The author has, in the pursuit of his studies on the fungi of Minnesota under the Geological and Natural History Survey of the state, be- come more or less acquainted with many of the plant diseases, and this volume is in part the result of such observations as were made in that work* The omission of some diseases is naturally unavoidable, and on the other hand it has been deemed advisable to include many diseases which are doubtfully of much importance in this state. These have been added either because their prevalence is to be expected on account of their existence in neighboring states, or on account of their general importance in other parts of the country. While not wishing to borrow trouble from the future, it is well to be forewarned. The old adage, "a stitch in time saves nine," is peculiarly appropriate. Again, plant diseases are here described which are economically of minor importance, but which are illustrative of certain impor- tant classes of diseases, and, as it has been pointed out that this work pretends to be chiefly educational, such diseases become, secondarily at least, of considerable im- portance. I wish to express my thanks to the following for assistance in various ways, as in the use of plates, photographs, material or literature : Mr« F. K. Butters, Profes- sor E. W. D. Holway, Mr. H. Cuzner, Professor F. L. Washburn, Miss D. Hone and Dr. H, L. Lyon of the University of Minnesota ; Mr. C. J. Hibbard of Minneapolis; Dr« Francis Ramaley of the University of Colorado; Professor G. F* Atkinson of Cornell University ; Professor R. S. Macintosh of the Alabama Experiment Station ; Dr. G. P. Clinton of the Connecticut Agricultural College ; Professor H. Marshall Ward, F. R. S., of the University of Cambridge; Professor Roland Thaxter of Har- vard University ; Professor F. C. Stewart of the New York Experiment Station ; Mr. F. J. Seavers of the University of Iowa; Mr. M. A. Carleton of the United States Department of Agriculture ; Professor H. L. Russell of the Wisconsin Agricultural Experiment Station; Professor B. M. Duggar of the University of Missouri; Mr. S. A. Sirrine of the New York Experiment Station ; Professor J. C. Blair of the Illinois Agricultural Experiment Station ; Mr. C. G. Loyd of Cincinnati ; Dr. J. C. Arthur of Purdue University ; Dr. . W. A. Kellerman of Ohio State University ; Professor H. L. Bolley of the North Dakota Agricultural College ; Professor B. D. Halsted of Rutgers College ; Professor B. O. Longyear formerly of Michigan State Agricultural College ; Minnesota Plant Diseases. ix Professor L. F. Kinney of the Rhode Island Agricultural Experiment Station ; Mr. J. B. Ellis of Newfield, New Jersey; and Professor G. Massee of Kew Gardens, Lon- don. To my wife I am greatly indebted for assistance in proof reading and in pre- paring the manuscript and index. To the following Experiment Stations I am indebted for the loan of plates for illustration: Kansas, Connecticut, New York (Geneva), New York (Cornell), Illi- nois, New Jersey, Massachusetts, Michigan, Rhode Island, Maryland. My thanks are also due the Goulds Manufacturing Co. of Seneca Falls, N. Y., for the loan of several electrotypes. Amongst the many well-known general works consulted, the following have proved particularly useful and have been freely used ; I wish here to acknowledge my indebtedness : Diseases of Plants, Tubeuf and Smith ; Pflanzenkrankheiten, Hartig Diseases of Trees, Hartig (translated by Somerville and Ward) ; Zerzetzungser scheinungen des Holzes, Hartig; Spraying of Plants, Lodeman; A Textbook of Plant Diseases, G. Massee; Die Natiirlichen Pflanzenfamilien, Engler and Prantl; and the older general works of Sorauer, von Tavel, Frank, Zopf and De Bary, I have made free use of the great literature of the bulletins and reports of the United States Agricultural Experiment Stations and especially of Connecticut Experi- ment Station Bulletin No. J42 and the Connecticut Report for J903, both of which were written by Professor G. P. Clinton. Where illustrations have been taken from other works credit is given in the proper place ; I desire here to acknowledge my indebtedness to the following publish- ers, for permission to copy illustrations : Julius Springer, Berlin ; Eduard Trewendt, Breslau; Gustav Fischer, Jena; The Clarendon Press, Oxford ; Longmans, Green & Co., New York; The Botanical Gazette, Chicago; Macmillan & Co., London and New York ; Wilhelm Engelmann, Leipzig. For the chapter arrangement of the descriptions of specific diseases in Part IIt I am indebted to the suggestion of Professor MacMillan. All figures designated as original were made by Mr. C. J. Hibbard under the Geological and Natural History Survey of Minnesota. The great majority were made under the direction and with the co-operation of the author ; the remainder under the direction of other members of the survey staff. To the Board of Regents of the University of Minnesota is due the credit for making financially possible the collection of material and illustrations and the publica- tion of this work. I am particularly indebted to Professor Conway MacMillan, at whose suggestion the work was undertaken, and without whose advice and assistance the publication would hiv£ bien impossible. Table of Contents. Jff PREFACE. INTRODUCTION i PART I General 5 CHAPTER I Fungi. Nutrition 7 CHAPTER II Fungi. Reproduction 21 CHAPTER III Fungi. Fungus Life Methods 35 CHAPTER IV Fungi. Plant Partnerships. Parasitism 48 CHAPTER V Fungi. Parasites on Animals 66 CHAPTER VI Fungi. Parasites on Plants 77 CHAPTER VII Fungi. Plant Disease 90 CHAPTER VIII Fungi. Kinds of Fungi. Algal Fungi 103 CHAPTER IX Fungi. Kinds of Fungi. Sac Fungi 117 CHAPTER X Fungi. Kinds of Fungi. Sac Fungi 135 CHAPTER XI Fungi. Kinds of Fungi. Basidium-bearing Fungi 153 CHAPTER XII Fungi. Kinds of Fungi. Basidium-bearing Fungi 170 CHAPTER XIII Other Disease-causing Organisms 189 CHAPTER XIV Economics. Prevention and Cure 201 CHAPTER XV Fungicides and Spraying Apparatus 211 PART II Special 233 CHAPTER XVI Diseases of Timber and Shade Trees. Timber Rots 235 CHAPTER XVII Diseases of Timber and Shade Trees. Timber Rots 260 CHAPTER XVIII Diseases of Field and Forage Crops 282 xii Minnesota Plant Diseases. CHAPTER XIX Diseases of Garden Crops 316 CHAPTER XX Diseases of Orchards and Vineyards 347 CHAPTER XXI Diseases of Greenhouse and Ornamental Plants 371 CHAPTER XXII Diseases of Wild Plants 385 INDEX 401 Index to Illustrations. Jff FRONTISPIECE. A wound parasite (Pleurotus nlmarius) on the trunk of a maple tree. Original. FIG. i. The mycelium of a food-mold fungus. After Zopf 8 FIG. 2. Various special absorptive or sucker threads of parasitic fungi. After Zopf 1 1 FIG. 3. Fungus strands and storage organs. Original 13 FIG. 4. Storage organ of a cup-fungus with fruiting bodies. Original. 14 FIG. 5. Strands of mycelial threads of the dry-rot fungus. Original. . 15 FIG. 6. "Shoestring" strands of mycelial threads of the honey colored mushroom. Original 17 FIG. /. Highly magnified view of section through the end of mycelial strand of the honey-colored mushroom. After Zopf 18 FIG. 8. Fairy rings of a mushroom fungus. Photograph by Dr. F. Ramaley 20 FIG. 9. Chief kinds of spores of fungi. Highly magnified. After vari- ous authors 22 FIG. 10. Various kinds of common fruiting bodies of fungi. After various authors 24 FIG. ii. Kinds of spores produced by one rust fungus (wheat rust) at different times. Highly magnified. After various authors 25 FIG. 12. A carrion fungus. Original 29 FIG. 13. A birds-nest fungus. After Engler and Prantl, and Sachs... 30 FIG. 14. Various explosive apparatuses for distributing spores. Mag- nified. After various authors 32 FIG. 15. A caterpillar-fungus spore, germinating. By the author 34 FIG. 16. A dung-dwelling fungus of the black mold group growing on horse dung. Photograph by F. K. Butters 37 xiv Minnesota Plant Diseases. FIG. 17. The same fungus as in figure 16, greatly enlarged. Micro- photograph by F. K. Butters 38 FIG. 18. An earth-dwelling fungus of the gill fungi. Original 39 FIG. 19. A wood-dwelling fungus on a dead stick of wood. Original.. 40 FIG. 20. A wound parasite. Original 46 FIG. 21. A lichen. After Atkinson 48 FIG. 22. A large witches'-broom on white pine. Photograph by R. S. Macintosh 52 FIG. 23. Witches'-broom on balsam fir, caused by a rust fungus. Original 53 FIG. 24. Witches'-broom on white spruce, caused by a mistletoe. Photograph by the author 54 FIG. 25. An enlarged view of the broom on the spruce shown in Fig. 24. Photograph by the author 55 FIG. 26. Birds-nest witches'-broom on red cedar, caused by a rust fungus. Original 57 FIG. 27. Oat smut. An accomplished parasite. After G. P. Clinton.. 59 FIG. 28. An endophytic mycelium between the cells of a grass grain. By the author 60 FIG. 29. Infection of a grass leaf by a rust fungus (wheat rust). After Ward - 61 FIG. 30. Beetle fungi attached to an insect. After Thaxter 68 FIG. 31. Various kinds of caterpillar fungi with fruiting bodies. Origi- nal 70 FIG. 32. Dead minnow with fish mold. Original 71 FIG. 33. A spore-case of a fish mold, showing escaping swimming spores. Highly magnified. After Zopf 72 FIG. 34. Damping-off of seedlings. After Atkinson. 77 FIG. 35. Strawberry leaf spot. Original 79 FIG. 36. Larch tree killed by the parchment pore-fungus. Original.. 81 FIG. 37. Fungus galls on the leaves of Labrador tea. Original 83 Minnesota Plant Diseases. xv FIG. 38. Two ways in which wood is destroyed by wood-rot fungi. Highly magnified. After Hartig 86 FIG. 39. A good example of an epidemic. Potato-blight has within a week entirely destroyed the potato plants in this field. After Clinton 99 FIG. 40. An epidemic of mildew on encumbers checked by spraying. After F. C. Stewart 101 FIG. 41. A lowly algal fungus. Highly magnified. After Schroeter. . 105 FIG. 42. Water and fish molds. Highly magnified. After various authors 106 FIG. 43. Sewer-pipe fungi. Highly magnified. After Pringsheim. ... 108 FIG. 44. Downy mildews. Highly magnified. After De Bary 109 FIG. 45. A downy mildew with the aspect of a white rust. Original. . in FIG. 46. A black mold. Highly magnified. After Zopf 113 FIG. 47. An insect mold. Highly magnified. After Brefeld 115 FIG. 48. Yeast fungus cells. Highly magnified. After Rees 118 FIG. 49. Plum-pocket fungus and loose-weft fungus. Highly magni- fied. After De Bary and Sachs 121 FIG. 50. A powdery mildew on common plantain leaf. Original 124 FIG. 51. The fruiting body of the powdery mildew of black haw, show- ing the appendages. Highly magnified. Microphoto- graph by E. W. D. Holway 125 FIG. 52. The fruiting body of the powdery mildew of willows, show- ing the appendages and spore-sacs. Highly magnified. Microphotograph by E. W. D. Holway 126 FIG. 53. Ergots of grasses. Original 127 FIG. 54. Ergot fungus on canary grass. Original 128 FIG. 55. Fruiting bodies and spores of the ergQt fungus. Variously magnified. After Tulasne and Brefeld 130 FIG. 56. A caterpillar fungus. Original 131 FIG. 57. A strangling fungus on grass leaves and stems. Original. . . . 132 xvi 'Minnesota Plant Diseases. FIG. 58. A strangling fungus. Fruiting bodies and spores. Variously magnified. After Winter and Brefeld 133 FIG. 59. Black knot of plum. After Clinton 135 FIG. 60. Two common types of "burnt-wood" fungi: a dung fungus (Sordariaceae), and a somewhat closely related fungus (of the family Chaetomiaceae). Magnified. Microphotographs by F. K. Butters 137 FIG. 61. A common cup-fungus growing on sunken sticks and appear- ing abundantly in the spring. Original 140 FIG. 62. A single sac and sterile threads from the palisade of sacs of the fungus shown in Fig. 61. Highly magnified. After Seavers 141 FIG. 63. A cluster of cup fungi showing cups just appearing above the ground. Original 143 FIG. 64. A cup fungus on the bark of a fallen tree. Original 144 FIG. 65. Cup fungus on decaying wood. Original 145 FIG. 66. Morel fungi. Original 147 FIG. 67. Saddle fungi. Original 148 FIG. 68. Truffles. Photograph by F. K. Butters 149 FIG. 69. Truffles. Fruiting bodies and spores, variously magnified. After F. K. Butters 159 FIG. 70. Two types of imperfect fungi. Magnified. After Tulasne. .. 151 FIG. 71. Smut spores, germinating. Highly magnified. After Brefeld 155 FIG. 72. Loose smut of wheat. Original 157 FIG. 73. Spores of rust fungi. Highly magnified. After Ward and Carleton 159 FIG. 74. Spores of rust fungi. Highly magnified. After Tavel 161 FIG. 75. Cluster-cups of ash-leaf rust fungus, on an ash twig. Mag- nified. Microphotograph by E. W. D. Holway 162 FIG. 76. Cluster-cup spores from the rust fungus of Fig. 75. Highly magnified. Microphotograph by E. W. D. Holway 163 Minnesota Plant Diseases. xvii FIG. 77. Spores of a grass rust fungus (Puccinia vexans). Highly mag- nified. Microphotograph by E. W. D. Holway 165 FIG. 78. Various basidia and spores of the lower basidium-bearing fungi. Highly magnified. After Brefeld 166 FIG. 79. Jew's ear fungus fruiting bodies on a dead branch of a balsam fir. Original 167 FIG. 80. A trembling fungus on the end of a log. Original 168 FIG. 81. Basidia and basidiospores of the higher basidium-bearing fungi. Highly magnified. After Brefeld and Schroeter. .. 170 FIG. 82. A smothering fungus growing on the ground. Original 172 FIG. 83. Club fungi on a decaying log. Original 173 FIG. 84. The coral fungus on the under side of a log. Original 174 FIG. 85. A pore fungus, growing on the ground. Original 176 FIG. 86. A stick-dwelling gill fungus, on a dead branch of a birch. Original 177 FIG. 87. The shaggy-mane fungus. Original 178 FIG. 88. The shaggy-mane fungus— a later stage than that shown in Fig. 87. Original 179 FIG. 89. The common wild mushroom fruiting body. Original 180 FIG. 90. A group of the common gemmed puff-balls, just before open- ing. Original 181 FIG. 91. The same group as in Fig. 90, taken two weeks later. Origi- nal 182 FIG. 92. Stalked puff-balls. Original 183 FIG. 93. Earth stars. Original .' 185 FIG. 94. A carrion fungus. Original 187 FIG. 95. A carrion fungus, photographed just after the breaking of the "egg," and while the cap was being lifted. Original.. 188 FIG. 96. Bacteria of the black rot of cabbage. Highly magnified. After H. L. Russell 189 FIG. 97. Bacteria of fire-blight of apples. Highly magnified. After B. M. Duggar 193 xviii Minnesota Plant Diseases. FIG. 98. Bacterial nodules on root of common bean. Original 195 FIG. 99. The bacteria of such root nodules of the pea family as are shown in Fig. 98. Highly magnified. After Atkinson... 196 FIG. 100. Slime molds. Variously magnified. After De Bary and Cienkowski 197 FIG. 101. Twig of a witches'-broom of spruce, showing the parasitic plants of the mistletoe, which cause the brooming of the branches. Photograph by the author 199 FIG. 102. A bucket pump. (The Deming Co.) 211 FIG. 103. A knapsack pump. (The Goulds Mnfg. Co.) 212 FIG. 104. A barrel pump. (The Deming Co.) 213 FIG. 105. A simple type of barrel pump used in the horticultural de- partment of the University of Minnesota Experiment Sta- tion. Photograph by R. S. Macintosh 214 FIG. 106. A gear-power force pump. (Victor Spraying Machine) 216 FIG. 107. A barrel pump in action, on the farm of B. Hoyt, St Anthony Park, Minn 217 FIG. 108. A powerful type of spray pump for orchard spraying. (Goulds Mnfg. Co.) 220 FIG. 109. A complex type of spray pump used at the New York Ex- periment Station for spraying several rows of asparagus at once. After S. A. Sirrine 222 FIG. no. The apparatus shown in Fig. 109 in action. After F. A. Sir- rine 224 FIG. in. Various fixings, tools and appliances for spraying apparatus. After J. C. Blair 228 FIG. 112. A convenient nozzle for spraying the under side of leaves. (Deming Co.) 230 FIG. 113. Nozzle for spraying plants in rows. (Goulds Mnfg. Co.). ... 230 FIG. 114. An effective nozzle for mist-like sprays. (Goulds Mnfg. Co.) 231 FIG. 115. Powder gun, with attachments. (Leggett) 231 Minnesota Plant Diseases. xix FIG. 116. Fungus fruiting boaies of a gill fungus, on street railway ties. Photograph by Dr. F. Ramaley 236 FIG. 117. A Stereum wound parasite. Original 241 FIG. 1 18. Partridge wood rot. Original 242 FIG. 119. The coral fungus, on the under surface of a log. Original.. 246 FIG. 120. The fruiting body of the dry-rot fungus. Original 245 FIG. 121. The dry-rot fungus on a pine board. Original 248 FIG. 122. The dry-rot fungus on pine boards, showing later stages of decay than that in Fig. 121. Original 249 FIG. 123. The fruiting body of the flattened pore-fungus, on a standing dead tree trunk. Original 252 FIG. 124. Fruiting bodies of the sulphur pore-fungus, on a dead oak stump. Original 253 FIG. 125. Fruiting bodies of the scaly pore-fungus seen from both sur- faces. After Loyd 254 FIG. 126. Fruiting body of the birch pore-fungus, on a branch of a white birch. Original 255 FIG. 127. Fruiting bodies of an undetermined pore fungus on a bass- wood log. Original 257 FIG. 128. Fruiting bodies of the honey-colored mushroom, at the base of a tree. Original 261 FIG. 129. Fruiting bodies of the fatty Pholiota in a wound of an oak tree trunk. Original 263 FIG. 130. The velvet-stemmed Collybia on a decaying log. Original... 264 FIG. 131. Fruiting bodies of the sapid Pleurotus on a standing yellow birch trunk. Original 265 FIG. 132. Fruiting bodies of the pine Lenzites, common on soft woods. Original 266 FIG. 133. Tar spots of willow and maple. Original 269 FIG. 134. Powdery mildew of willow leaf. Original 273 FIG. 135. Powdery mildew of elms on an elm leaf. Original 274 FIG. 136. Pine knot on Scotch pine. Original 276 xx Minnesota Plant Diseases. FIG. 137. Poplar leaf rust. Original 278 FIG. 138. Willow leaf rust. Original 280 FIG. 139. Wheat rust. Stems of wheat, showing opened and unopened black clusters of winter spores. Slightly magnified. Original 283 FIG. 140. Wheat rust. A section of such a stem as is shown in Fig. 139, highly magnified. Microphotograph by E. W. D. Holway 284 FIG. 141. Oat stems and leaf bases, with clusters of summer spores of the oat rust. Original 285 FIG. 142. Spores of the common "black rust" of wheat. After Arthur and Holway 286 FIG. 143. Spores of the crown rust of wheat. Highly magnified. After Arthur and Holway 287 FIG. 144. Cluster-cups of the crown rust of wheat, on swollen cushions of the stem of the alder-leaved buckthorn. Photograph by Arthur and Holway 288 FIG. 145. Cluster-cups of the black or stem rust of wheat, on stems and leaves of the barberry. Photograph by Arthur and Hol- way 290 FIG. 146. Loose smut of oats. Original 293 FIG. 147. Stinking smut of wheat, showing smutted grains and spores. Variously magnified. After Tubeuf 296 FIG. 148. Smut of corn. On the leaves and tassels. After Clinton. .. . 298 FIG. 149. Corn smut on an ear of corn. Original 299 FIG. 150. Head smut of sorghum. After Kellerman 301 FIG. 151. Grain smut of sorghum. After Kellerman 302 FIG. 152. Powdery mildew of grasses on wild grass-plant leaves. Original 304 FIG. 153. "Black mold" of clover on leaves of white clover. Original 305 FIG. 154. The ergot fungus on rye. After Clinton 307 FIG. 155. Storage organs or ergots of ergot fungi on various grasses. Original 308 Minnesota Plant Diseases. xxi FIG. 156. Flax wilt; wilted seedlings. After Bolley 3II FIG. 157. Spores of the flax wilt fungus, highly magnified. After Bol- le^ 312 FIG. 158. Flax wilt; the fungus threads around the root of an attacked flax plant. Highly magnified. After Bolley 312 FIG. 159. Flax wilt; a section of a flax root, with fungus threads and spores at the surface. Magnified. After Bolley 313 FIG. 1 60. Orange rust of raspberry and blackberry. Original 316 FIG. 161. Winter spores of the asparagus rust. Highly magnified. Microphotograph by E. W. D. Holway 318 FIG. 162. Rust of bean. After Clinton 3I9 FIG. 163. Pore-fungus root-rot of currant. Original 321 FIG. 164. Potato scab. After Clinton 326 FIG. 165. Anthracnose of bean. After Halsted 328 FIG. 166. Potato blight. Early stages of the blight on the leaves. After Clinton 332 FIG. 167. Potato blight. Later stages on the leaves. After Clinton... 333 FIG. 168. Downy mildew of muskmelon. Blighted vine in the field. After Clinton 335 FIG. 169. Downy mildew of muskmelon, showing the under surface of an attacked leaf. After Clinton 336 FIG. 170. Downy mildew of muskmelon. Under surface of an attacked leaf. After F. C. Stewart 337 FIG. 171. Downy mildew of melons and cucumbers. Spores and spore- bearing threads. Highly magnified. After Humphrey and F. C. Stewart 338 FIG. 172. Bacterial rot of potato. After Clinton 340 FIG. 173. Bacterial rot of squash. After Clinton 341 FIG. 174. Black rot of cabbage. A badly infested field. After H. L. Russell 342 FIG. 175. Black rot of cabbage. Artificial infection of cabbage plants. After H. L. Russell. . 343 xxii Minnesota Plant Diseases. FIG. 176. Black rot of cabbage. Bacteria, highly magnified. After H. L. Russell 343 FIG. 177. Black rot of cabbage. Cabbage heads, apparently sound, are attacked by the rot. After H. L. Russell . 344 FIG. 178. Black rot of cabbage. A cabbage leaf showing the manner of infection. After H. L. Russell 344 FIG. 179. Club root of turnips. After Halsted 345 FIG. 180. Club root of cabbage. After Clinton 346 FIG. 181. Cedar apples of red cedar. Original 348 FIG. 182. Rust of apple leaves. After Clinton 349 FIG. 183. Apple scab on the fruit. After Clinton 351 FIG. 184. Apple scab on the fruit. After Longyear 351 FIG. 185. Apple scab on a twig. After Clinton 352 FIG. 1 86. Apple scab on the leaf. After Longyear 353 FIG. 187. Spores of the apple scab fungus. Highly magnified. After Longyear 354 FIG. 1 88. Blue-mold fruit rot of apple. After L. F. Kinney 355 FIG. 189. Blue-mold fruit rot of apple. Accessory spores of the fun- gus, highly magnified. After L. F. Kinney 356 FIG. 190. Bitter rot of apple. After Clinton 357 FIG. 191. Black knot of wild cherry, showing various stages in the de- velopment of the knots. Original 359 FIG. 192. Powdery mildew of plums and cherries. Variously magni- fied. After Ellis 360 FIG. 193. Plum Pockets. Photograph by H. Cuzner 362 FIG. 194. Black rot of apple. After Clinton 364 FIG. 195. Fire blight of apples. Bacteria which cause the disease. Highly magnified. After B. M. Duggar 364 FIG. 196. Downy mildew of grape. Under surface of an attacked grape leaf. Original 368 FIG. 197. Downy mildew of grape. A healthy and an attacked bunch of grapes. Original 369 Minnesota Plant Diseases. xxiii FIG. 198. Downy mildew of grape. Spores and spore-bearing threads. Highly magnified. After Millardet 370 FIG. 199. Leaf rust of roses. The cluster-cup stage on the stems and leaves. Photograph by H. Cuzner 374 FIG. 200. Leaf rust of roses. Stem with groups of cluster-cups. Origi- nal 375 FIG. 201. Leaf rust of roses. Variously magnified. After Massee 376 FIG. 202. Powdery mildew of lilac. Original 377 FIG. 203. Powdery mildew of roses. A leaf of the rose attacked by the disease. After Clinton 378 FIG. 204. Powdery mildew of roses, showing the superficial mycelium and summer spores on the leaves. After Tulasne 379 • FIG. 205. Golden-rod rust. Original 388 FIG. 206. Sunflower rust. Original 389 FIG. 207. The stem rust of the cowberry. Highly magnified. After Hartig 390 FIG. 208. Rust of wild sarsaparilla. Original 391 FIG. 209. Mint rust. Original 393 FIG. 210. Powdery mildew of composites, on the leaf of the great rag- weed. Original 396 FIG. 211. Gall fungus on the wild peanut. Original 398 Introduction. The diseases of plants and their causes may be grouped as follows : Organic diseases, i. e., those caused by living organisms such as: Fungi, Bacteria. Slime molds. Flowering plants. Insects and other animals. Inorganic diseases, i. e., those due to other causes than living organisms : Unfavorable conditions of soil, etc. Unfavorable conditions of weather, etc. It is not the purpose of this work to consider all of the dis- eases of Minnesota plants. The attack of insects furnishes a vast field of research which is best left to the entomologist. By far the most widely distributed and most destructive of Minne- sota plant diseases are organisms belonging to the plants known as fungi. Bacteria are responsible for a considerable number and the fungus-like animals, known as slime-molds, are respon- sible for a few. In addition the flowering plants cause several diseases. There are also to be considered those diseases which are caused by inorganic agencies as drought, heat, wind, hail, lightning, frost-cracks, sunscalds, etc. This work will not ad- mit of a discussion of the latter group. It is well at the outset to note that disease cannot be easily defined. One might consider any variation due to the derange- ment from the most favorable conditions of the life of a plant as a disease. The most favorable conditions in all respects are seldom, if ever, realized. When the favorable conditions of life are so seriously interfered with by any agency, so that the life 2 Minnesota Plant Diseases. of a part of a plant or of the whole plant is threatened, we rec- ognize disease in that plant. The change in favorable condi- tions may be so slight that the shortening of the life of the plant or its parts is not apparent. One does not recognize disease in such a case, although it is essentially similar to that of well- recognized diseases. There are, then, between health and dis- ease in plants imperceptible gradations and no sharp lines of demarcation. A farmer who intelligently strives for all of the most favorable conditions of his crop is in reality combating disease. A great loss to agriculture annually occurs which does not usually pass for disease. When the grower of plants real- izes this, and when he joins his efforts with those who are seek- ing methods of combating diseases, then more rapid strides will be possible in methods of investigation and prevention. The more knowledge a farmer possesses of the conditions favorable and unfavorable to the numerous diseases which affect his crop, just so much more successful will he be in his efforts toward preventing disease. Agriculture really resolves itself into one great problem, the prevention of plant disease in the broader sense. There are three factors to be considered in a plant disease : (1) The immediate cause of a disease, e. g., fungi, bacteria, insects, etc., as enumerated above. (2) The immediate effect in the anatomy, form and physi- ology of the host plant and the effect in inheritance. (3) The previous condition and disposition of plants which may seriously affect the susceptibility of those plants to a cer- tain disease ; in other words, the predisposition of plants toward disease. It is therefore apparent that one must study not only the immediate cause of a disease but the predisposition or immu- nity of plants toward that disease. An appreciation of these principles finds expression in the selection of varieties for spe- cific purposes and in the more detailed study of the life-histories of diseases. By such study an exact knowledge of the habits of a parasite are obtained and it is only by means of this knowl- edge that we can. intelligently devise methods of prevention. Too much stress cannot be placed on the necessity for accurate work in the observations of the habits of a parasite and of its Minnesota Plant Diseases. 3 life-history. All of those diseases which are at present success- fully combated have been dealt with only after a thorough knowledge of their habits. The treatment of oat smut, for in- stance, is based on the knowledge that infection of the oat plant takes place when the plant is in the seedling stage and from spores found usually clinging to the oat grains. The predisposition of plants toward disease is a subject which at this point is to be dealt with only in passing, and will receive more detailed attention in later chapters. Part I. of this work will deal in general with those groups of plants, particularly the fungi, which furnish the causes of dis- eases in plants and with general methods of combating diseases, etc. Part II. will be given up to a consideration of specific dis- eases of Minnesota plants. PART L— GENERAL. Chapter I. Fungi. Nutrition.-, H };/ Jff •"/.'.. : , - , What the fungi are. As understood today, the plants known as fungi do not include the bacteria and the slime molds. The bacteria are plants which find their closest affinities with the blue-green algae. Slime-molds possess fructifications which have at least great superficial resemblance to those of the fungi, but their vegetative life is similar to that of the lowest order of animals. They are therefore known appropriately as fungus- animals. The fungi are all devoid of leaf-green. They hold this char- acter in common with bacteria, slime-molds and many flower- ing plants. The lack of leaf-green is the result of a different habit and nutrition method from that of leaf-green-bearing plants. The latter can utilize constituents of the air and water, together with mineral salts from the soil, and build them up. with the power of sunlight, first into starch and then into the more complex substance known as protoplasm or living sub- stance. The loss of leaf-green indicates that a plant has no longer any use for a starch-forming apparatus, but since it still needs starch it must obtain such material in a manufactured condition. Fungi are therefore dependent upon other plants or animals or upon the products of these organisms for food. Al- though lack of leaf-green is not characteristic of fungi alone but is shared by certain other plants or groups of plants, we find that the fungi do possess a distinguishing mark in the structure of the vegetative portion of their bodies. That portion of the plant which is concerned with the build- ing up of the individual plant itself is known as the vegetative portion, while that which is concerned with the production of cells for the development of offspring is reproductive. The vegetative portion of a fungus is known as a mycelium and has 8 Minnesota Plant Diseases, a characteristic structure and method of growth. This myce- lium is composed of fine microscopic threads, more or less branched and densely interwoven to form loose, woolly masses, as in bread mold, or may even be compacted to form solid bodies. All fungi reproduce in some form by means of micro- scopic cells, more or less spherical in shape, and often as small as 1/2000 of a millimeter in diameter. They are usually, how- ever, larger. These tiny cells are known as spores and have various forme and methods of production, which are character- FIG. 1. — The mycelium of a food-mold fungus (Penicillium). A. Mycelium which is entirely absorptive and tufts (t) of spores (reproductive tract). The original spore from which the mycelium grew is seen at a. B. Highly magnified view of spore tuft. After Zopf. istic for different groups of fungi. There is, however, no spore form or spore receptacle which is common to all fungi, nor are spores themselves confined to fungus plants. Plants as well as animals can usually be best understood by their ancestry. The fungi have all descended from the algae, probably not, however, from one, but from several groups, e. g.. Minnesota Plant Diseases. 9 from the flower-pot algae, the green felts and the pond scums, and possibly from the red sea-weeds. The fungi therefore comprise low forms of plant life which have descended from algal stock and which by a change in their nutritive methods have lost their leaf-green and have come to possess a vegetative mechanism, composed of more or less branched threads known as a mycelium. The number of fungi in Minnesota is undoubtedly very large. It has been estimated at between 2,500 and 3,000, out of a total number of 7,000 Minnesota plants. The minute size of many of these fungi, — some of the entire plants cannot be seen without the aid of a hand-lens, — the difficulty of observation, the great resemblances of forms and the complex methods of life make the determination of these plants a slow task, and the exact number of Minnesota fungi will probably not be known for some years. The rate of constant additions of new forms is sufficient indication of the very large number which exists in the state and points towards a confirmation of the above esti- mate. The fungus method of obtaining nutrition. It was stated above that fungi had lost the leaf-green of their algal ancestors and were therefore unable to make starch from water, soil and air constituents but compelled to derive their elaborated food from other sources. Two methods have been adopted. In one the fungus derives its nutritive material directly from living plants. Such are parasites, and the plants upon which they feed are known as host plants. In the other method the fungus derives its prepared food from the dead products or remains of animals or plants, as leaf-mold, bread, preserves, etc. Such plants are known as saprophytes. In both of these cases the food obtained is at least partially prepared. How the nutritive method is expressed in structure. It is a law which covers all living things, plants as well as animals, that the complexity of the structure of an organism depends on the amount and kinds of work which it can perform. When an organism has its food prepared by no effort of its own, it soon shows the loss of power to do that work. This loss of power is usually expressed in loss of certain structures, or in the simplifying of such structures. Such an effect is commonly io Minnesota Plant Diseases. described as degeneration. It is a noteworthy fact that such a plant may be very well adapted for obtaining food in its own way, and in this respect may be highly specialized. The wheat- rust, for instance, is very highly organized and is very closely adapted to its own manner of life. The fungi are specialists along certain lines of obtaining food and are in these lines more highly specialized than leaf-green-bearing plants. Plants with such a habit of life do not need the elaborate starch-making machinery of higher plants, as of ferns and flowering plants. It is easier and more economical for fungi to reduce their vege- tative areas and hence, to simplify their structure. It is a case of economy on the part of the plant. In general, all plants, whether fungi or flowering plants, when devoid of leaf-green, are efficient specialists in their absorptive methods while at the same time the vegetative area may be comparatively simple. It must therefore be understood that when these plants are called degenerate it is only in this one aspect of vegetative structure that they are correctly so called. In absorptive power and in reproduction they may be fairly complex. It is also well known that parasitism in animals also results in degeneration of structure. There are a large number of worms, such as tapeworms and thread worms, numerous insects, such as fleas and bird lice, and even vertebrates, as the hag fishes, which are parasitic in their habits. In all of these cases simplification or degeneration of the animal body results. Or- gans of locomotion, sense organs, digestive tracts are all pro- foundly affected; either very much reduced or lost entirely. Many flowering plants have also adopted either parasitic or saprophytic habits. Familiar examples are found in the dodder and coral-root orchid. The dodder is usually found in swampy places or in clover fields and is a confirmed parasite. It has lost its leaf-green except in very early life and is consequently in later life yellowish in color. The coral-root orchid grows on leaf mold in the deep woods and is a saprophyte in habit ; it has also lost its leaf-green; and its leaves, as in the case of the dodder, are reduced to small scales, useless for starch-making purposes. On the other hand, all parasites and saprophytes, whether plants or animals, have well developed systems of ab- sorption and reproduction. The fungus system of absorption, Minnesota Plant Diseases. 1 1 at least in higher forms, is highly organized. In lowly forms of fungi, where the plant body is but a single, small, more or less rounded cell of microscopic size, absorption takes place over the entire surface of the little plant and there is no specialized region for the performance of this function. In all of the higher forms absorption takes place through a system of much- branched, fine threads of microscopic size. In a mushroom, for instance, these threads penetrate the soil for a considerable distance, often for feet and even yards. FIG. 2. — Various special absorptive or sucker threads of parasitic fungi, m. The mycelial threads. The sucker threads (H) are seen in the host plant cells. I. A downy mildew. II. Rust fungus. III. Protomyces (a fungus with a doubtful systematic position). Highly magnified. After Zopf. The absorptive area is built upon a similar physiological prin- ciple to that of the root system of flowering plants, for in these absorption takes place at the surface of very fine hairs, which are borne on the surface of the younger roots. True root hairs and fungus absorption threads embody the same advantage in the presentation of a large absorbing area. In the fungus the threads branch profusely and are of great length, and thus a 12 Minnesota Plant Diseases. greater area of soil is drained of its nourishment. Root hairs of flowering plants never branch, but new ones are constantly being formed near the tip of the growing rootlets, thus effect- ing a similar result to that of the branched mycelium of the fungus. The absorptive system of parasites often consists of a similarly branched mycelium which runs between the cells of the plant upon which it feeds. Some of the branches of these fungus threads are of a special kind and penetrate into the cells of the host plant. Parasitic plants may not have such a richly developed absorptive system as a mushroom, but in other re- spects may be more highly specialized. The mycelium of a highly organized parasite is usually only able to obtain nour- ishment from certain species or groups of species of plants. For instance, certain rusts are capable of getting nourishment only from one kind of grass plant. It will be seen from these considerations that the absorptive system of this group of plants, whether parasites or saprophytes, is, in general, well de- veloped. Parasitism and saprophytism. Parasites are usually de- scribed as those plants which obtain their nourishment directly from living plants or animals. They are so organized that, when their nourishing threads come into close contact with cer- tain living plants or parts of plants, they answer to certain im- pulses, sending special branches directly into the living tissues and there absorbing nutrition. Saprophytic plants, on the other hand, are not reacted upon by living plants and are com- pelled to get their nourishment from the dead products of plants or animals. The real substances which are absorbed by parasites and saprophytes may not be different in their chem- ical natures but the methods of obtaining them differ. The parasite has learned to respond to certain impulses, which it re- ceives when it comes near to another plant, and by this response obtains nutrition. True saprophytes never respond to such an impulse. They live on ground rich in leaf mold or in decaying wood, or on dung of animals, on remains of animal life or on still other products of living plants or animals, but never upon the organism when the latter is still alive. Parasites are limited in their size by the size of their host- plant, hence they are usually very small — often microscopic in Minnesota Plant Diseases. T^ size. Being limited in size, they often live for a long period through which they produce their reproductive bodies and thus compensate for lack of size. In some cases they produce dif- ferent kinds of spores at different seasons. Such is the case in the fungus which causes rust diseases of grains. The sapro- phyte, on the other hand, has often an unlimited supply of mate- FIG. 3. — Strands and storage organs. 1. Strands of a stalked puff-ball (Tylostoma) with young fruiting bodies attached. 2. Strands and storage organs of a carrion fungus (Dictyophora ravenellii). Original. rial at its disposal. Moreover, this food material is easily avail- able and large plant bodies can thus be built up. Such is the case with a great many saprophytes, especially those of the mushroom group, puff-balls, etc. Only one effort a season may 14 Minnesota Plant Diseases. be made by the plant to produce reproductive bodies and then one grand effort is made. A single mushroom may produce mil- lions of spores and shed them all in a single day. Not all para- sites, however, are small; but in some cases, as in the wound parasites, they may produce large shelf-like fruiting bodies. These plants are often saprophytic at first, becoming parasitic later. Storage organs. Most fungi use the food materials which have been absorbed from their various sources, for the immedi- ate production of fruiting bodies. Consequently the fungus con- sists almost entirely of these two regions, the absorptive myce- FIG. 4. — Storage organ of a cup fungus (Sclerotinia) with fruiting bodies (stalked cups) which have grown from the storage organs. Original. lium and the reproductive organs. Some fungi, however, have learned to store food for future use and are thus able to collect considerable material, before attempting the formation of spore-bearing organs. The ergot of rye is such a storage or- gan, formed by a fungus parasitic on the rye. The fungus ap- propriates the nutrient material of the young grain and builds up a solid elongated or roundish body which, when mature, be- comes dark violet colored or blackish. This body is composed of parallel threads of the fungus tightly compacted together and Minnesota Plant Diseases. contains nutrient mate- rial in the form of oils and other compounds. This ergot remains dor- mant through winter and in the spring pro- duces reproductive bod- ies. Certain carrion fun- gi form storage organs. They are found under the ground, developed on strands of the mycelium. In this case the storage organ has packed up its food material in the form of a starch peculiar to fungi and known as fun- gus starch. Certain pore fungi produce very large underground storage or- gans. Such is probably the "Tuckahoe Indian Bread" of the southeast- ern states. This storage organ is often about the size of a small cantaloupe and of heavy doughy consistency. A certain pore fungus of Australia produces storage organs of immense size and these are used by the natives for food. The caterpillar fungus furnishes an ex- ample of a storage organ of some interest. The fungus attacks living cat- erpillars and the myceli- FIG. 5. — Strands of mycelial threads of the dry- rot fungus (Merulius lacrymans). Figs. 120, 121 and 122. Original. See also 1 6 Minnesota Plant Diseases. um finally gains entrance to the interior of the insect body. By continued growth of the fungus the caterpillar is killed. Its substance is absorbed and appropriated by the parasite, which finally replaces all insect parts with densely woven threads packed with nourishment. There is thus produced a complete cast of all parts of the caterpillar, life size, composed of the threads of the fungus. After a rest period, this mummy or storage organ produces a stalked reproductive body. In New Zealand certain very large caterpillars are thus attacked and the resulting storage organs are used as a food by the natives. They are known as vegetable worms. Fungus Shoestrings or Strands. One often finds in decaying logs or in soil where an abundance of woody material is present, cord-like strands, often whitish in color, or in other cases very dark. By tracing them along one finds them connected with puff-ball fruiting bodies, or carrion fungi or gill fungi. Those strands formed by the puff-ball or carrion fungus are whitish in color and branch considerably ; some of the branches are very small and occasionally meet each other, fusing together to form a network. These threads are not absorptive in their function, although the smaller branches connect directly with the ab- sorptive mycelium. They serve probably in part to store up a certain amount of nourishment, but their chief purpose is to distribute as widely as possible the fruiting bodies and to enlarge the territory from which the fungus draws its nutrition. In re-' spect to the enlargement of the spore distribution such strands function as do the runner stems of higher plants. Perhaps the most common of these strands and those to which the name shoestring more properly applies, are the gill- fungus strands, particularly those of the honey mushroom, which is abundant everywhere in the fall. These strands are found both in the ground and under the bark of trees. They are dark-colored exteriorly and branch profusely and, like those of the puff-balls, may form elaborate networks. The older strands look somewhat like shoestrings. They may attack roots of trees, penetrate the bark and spread under the latter to form an absorptive mycelium which is parasitic, and which may finally kill the tree. Under the bark of such dead trees one finds large networks of shoestring strands and at the base Minnesota Plant Diseases, 17 of the trunks will arise the honey-colored mushroom, which usually occurs in great clusters. FIG. 6. — "Shoestring" strands of mycelial threads of the honey-colored mushroom (Armillaria mellea). (See also Fig. 128.) Original. Physiology of the Mycelium. The mycelium arises from the spore by the germination of the latter. The spore sends 1 8 Minnesota Plant Diseases. out one or more little tubes which elongate and finally, by branching, produce numerous threads; the spore is then seen at the center of a system of radiating threads, like the hub of a wheel and its spokes. These threads soon branch pro- fusely and now a circular, densely interwoven network is produced which keeps on enlarging, thus encroaching upon new areas of nu- tntion. If the spore should be placed in nutrient jelly, where its'5 environments in ^ all directions are alike, the result- ing mycelium would be ball- shaped in outline ; but if the myceli- um is DrodtlCed ill SUCh a Olace aS the mold soil on the forest floor, the symmetry of the form is interfered with by various obstacles. In general, a mycelium would tend to become circular in outline as seen from above. Such a myce- lium is often seen in the production of what are called fairy rings. Many gill-fungus mycelia grow from year to year and at the proper season of each year produce a crop of fruiting bodies at the surface of the ground. These are formed at the end of the mycelium and hence come to< stand in a circle. One circle appears each year, becoming larger year by year. The peculiar life habits of many fungi bring with them peculiarities in the development. Many fungus spores will ger- minate between temperatures a little above freezing, i.$°-2°C., and 4O°-43°C., but best at about 2$°C. Such as are required to pass through the alimentary canal of certain animals before germinating demand, in general, higher temperatures. One of the gaseous constituents of the air, oxygen, is necessary to the germination of spores of fungi. Every housewife knows ly magnified view of section through end of mycelial strand of honey-colored mushroom, showing compactness of central portion (c and d) and loose threads at the surface (a and b). Highly magnified. After zopf. Minnesota Plant Diseases. 19 that if all of the air is excluded from a jar of preserves no molds will develop. The spores of parasitic fungi will usually germinate if placed in water. They often require to be kept for a certain time and are often adapted for certain seasons. For instance, the black rust spores of wheats and grasses usually will not germinate until the following spring. A germinating spore of a true par- asite must be brought into contact with its proper host, or it will soon die for lack of food. When brought into contact it commences very soon its parasitic life. The spores of many saprophytes, on the other hand, require nutrient substances before they will germinate. It is often a matter of very exact requirements as, for instance, in the case of the common com- mercial mushroom. It is only within the last few years that the commercial mushroom spore has been observed germinat- ing. The continuation of the growth of the mycelium takes place at about the temperature of the germination. Light is not a necessary condition for growth, for it is not an essential in the building up of starch in fungi, as it is in the case of any of the leaf-green-bearing plants. Hence one finds fungi devel- oping luxuriantly in caves and cellars. Light, however, some- times influences the formation of the fruiting bodies. The food material of most saprophytic fungi is required to be of a slightly acid composition. The concentration of compounds found in the nutritive substances affect profoundly the develop- ment of the fungus. Certain fungi which develop well in a weak solution of sugar, cannot grow in a very concentrated solution, a principle which is utilized in the preserving of fruits. Such fungi as the wood-inhabiting and insect-inhabiting forms illustrate well the method of attack of many fungi. The timber parasites and saprophytes exude from their threads a chemical substance which attacks the wood tissues and destroys the woody properties. The wood is thereby reduced to punk. Insect-inhabiting forms exude a substance which attacks and disintegrates the chitinous coverings of the insect, thus gain- ing entrance for the fungus to the soft parts of the insect. The age of a mycelium varies considerably in different fungi. Some live for but a few days, some live indefinitely, being lim- ited only by the absence of nutrition, and others again are reg- 20 Minnesota Plant Diseases. ularly perennial. The latter include both saprophytes and parasites. The fairy-ring mushrooms are good examples of the former, while of the latter, illustrations are found in those rust fungi which attack balsam fir and other cone-bearing plants and form witches' brooms. The mycelium of the fungus caus- ing smut of grains is of a peculiar kind. It often finds its way into the host plant when the latter is very young and tender, and continues to grow in the delicate growing parts and dies FIG. 8. — Fairy rings o >f a mushroom fungus (probably a Lepiota). Photographed by Dr. Ramaley. F. behind in the mature tissues. The examination of such a plant would show a mycelium only in the growing part of the stem. When the young grains are formed the mycelium develops in their tissues, completely destroying them and forming smut spores in their stead. The mycelia of many fungi are capable of resisting many unfavorable conditions, reviving again immediately upon the return of propitious surroundings. Evidence of such power is seen in any woods when a heavy rain follows on a long period of drought. On all sides one finds fungi improving to the full- est their opportunity of favorable weather. Chapter II. Fungi* Reproduction. The fungus method of reproduction. Fungi reproduce by means of very small bodies of microscopic size, which are known as spores.* All of the spores of fungi are not similar in origin, structure or appearance, but differ in these respects very considerably. Some spores are pinched off, as it were, of special fungus threads, often in rows, as in the summer spores of mildews. Others, again, are formed in cases, as in the small black heads of black molds ; or in sacs, as in the morels and cup fungi. Again, a spore may be formed as the result of a breeding act — i. e., the fusion of two sexual elements which may be both alike or may be male and female. Some spores are provided with fine thread-like processes and by whipping these about can swim around in the water. Such spores are found in the potato-blight and in many water-inhabiting forms, as fish-molds. Many spores are capable of germinating im- mediately while others require a long rest period and are there- fore provided with thick protective coats. The summer or red-rust spores of grass rusts commence to grow as soon as they are ripe, if the conditions are otherwise favorable, and this fact accounts in part for the rapid spread of rust in certain seasons. The winter spores of rust, or black rust, have thick protective coats and usually rest over until the following spring, when they continue their further development. In the bread-mold and its allies, in the fish molds and in the potato-blight relatives, no complex organs are formed upon which the spores, whether pinched off or in cases, may be ag- *The term spore might b2tter, as is advocated by many botanists, be retained for the equivalents of the spore of the moss sporogonium and all other sporophytes. This restric- tion would exclude the term from the realm of fungi with the exception of perhaps the sac spores of the sac fungi and certain spores of the algal fungi, and perhaps also the sporidia of the rusts. Convenience and established usage would seem to counsel here the retention of this teim in the older and commonly accepted sense. 22 Minnesota Plant Diseases. gregated together. They are found on threads more or less loosely scattered about. In many higher fungi, however, the spore cases or sacs are borne on special structures, called fruit- ing bodies, though, of course, this term does not imply that they are at all similar or equivalent to fruits, as the gardener or horticulturist understands that term, when applied to parts of FIG. 9. — Chief kinds of spores of fungi. 1. Sac with spores. 2. Basidia with basidio- spores; a, b and c stages in spore formation. 3. Spore case of mold containing numer- ous spores. 4. Tuft of pinched-off spores of blue mold. 5. Swimming spores of an algal fungus. 6. Spores of a black mold produced by a breeding act — stalks of the breeding cells are seen below the spore. 7. Spores of an insect mold. 1, 2 and 5 after DeBary; 3 after Sachs; 4, 6 and 7 after Brefeld. flowering plants. The best known of such fruiting bodies are the common structures known as mushrooms and toadstools, which in typical forms are composed of a stalk and an umbrella- like cap, on the under surface of which are leaf-like plates, run- ning from the edge to the top of the stalk. The spores are Minnesota Plant Diseases. 2^ «3 borne all over the surface of the plates, or gills, as they are termed, and the spore area is thus very greatly increased in size. Such fungi are known as gill fungi. Again, shelf fruit- ing bodies are produced, which have holes all over the under surface, as though pricked with a needle. The spores are formed over the entire surface of these holes or pores. These fungi are known as pore fungi. The fruiting bodies of other fungi, again, may be more or less club shaped and branched or unbranchecl, or they may be provided with numerous teeth as in the bear's-head fungus. The puff balls are very common ob- jects, especially towards the fall of the year; they are closed fruiting bodies, with one or more enclosing membranes, which open by a definite hole at the top, to allow of the escape of the ripe spores. By pressing such a puff ball a dust of spores is thrown out to the wind and scattered considerable distances. Many relatives of the puff ball form fruiting bodies under- ground, which look somewhat like truffles. The curious little beaker-shaped structures containing egg-like objects are fruiting bodies of the "birds-nest" fungi and the fruiting bodies of the carrion fungi are still more remarkably elaborated. Here the spores are borne on the top of a very elastic stalk and are found in a sticky mass which has an odor of carrion and is much sought after by insects. The whole is enclosed in an elastic covering which ruptures only when the spores are ripe and then the stalk, previously held under pressure, is released and lifts the spore area up very quickly into the air. In the mildews, such as the common mildew on lilacs, in addition to the loosely scattered summer spores, fruiting bodies are found in the fall. They are usually very much smaller than a pin- head. Under a microscope they are seen to be little, hard, black-walled, capsule-like objects with curious appendages and containing one or more sacs of spores. The black-knots on cherry trees are fruiting bodies which contain, scattered over the surface, numerous minute, pear-shaped depressions, which are partially lined with sacs of spores. Very common in most places, on wood or on the ground, are the cups of the cup- fungi. These are fruiting bodies of various sizes with, in gen- eral, a cup or beaker shape and are often brightly colored. The inside of the cup is lined with sacs which burst open and Minnesota Plant Diseases. FIG. 10. — Various of the most common kinds of fruiting bodies of fungi. 1. Birds-nest fungus. 2. A gill fungus. 3. Caterpillar fungus, one on grub and other on fly. 4. Club fungus. 5. Carrion fungus. 6. Pore fungus. 7. A morel. 8. Puff-ball. 9. Truffle. 10. Cup fungus. 11. Sac-spore-capsule of powdery mildew (highly magnified). 1-8. After Engler and Prantl; 10, After Rehm; 9 and 11, after Tulasne. Minnesota Plant Diseases. forcibly eject their spores. Often by a change in the atmos- pheric conditions a large number of sacs burst at once and clouds of spores can be seen to ascend from the cup. The truf- fles have underground closed fruiting bodies which are related to the cups but never open except by decay of the walls. The morels and their allies have cups which are turned inside out, as it were, and are furthermore usually much wrinkled, and borne on stalks. Another very important phase of reproduc- tion in fungi lies in the kinds of spores produced by a given fungus. One and the same fungus may often produce more than one kind of spore. In fact, some fungi produce as many as five or six kinds. The wheat-rust, for example, forms one or more, commonly two, — kinds of spores in the spring, another in summer and anoth- er in the autumn and when the autumn spores grow in early spring still another kind is produced. These spore forms fol- low in a certain way the seasons. The mil- dew, for instance, has summer spores and winter spores. In oth- er fungi the various forms may be called forth by differences in the substances upon which the fungus grows. In some fish-molds the production of the different spores can be exactly controlled by changing the food sub- stances. Sometimes a fungus which is or has been capable of producing several spore-forms continues under certain condi- tions to produce only one kind of spore. Our knowledge of such a fungus is incomplete until we know the other spore- forms which it is capable of producing. There is a vast num- FIG. 11. — Kinds of spores produced by one rust fungus (a wheat rust) at different times. 1. Winter spore. 2. Basidiospore. 3. Cluster-cup spore. 4. Pycnidial spore (probably a function- less relic of a male sexual cell). 5. Summer spore. 1, 2, 4 and 5, after Ward; 3, after Ar- thur and Holway. 26 Minnesota Plant Diseases. her of such imperfectly known fungi, many of them being of great economic importance. They are usually designated as "Imperfect Fungi" and are classified temporarily according to a very artificial system under what are usually termed "form genera." This selection of fungi for special substances, for the pro- duction of certain spores, and the production of different spores according to seasons, has given rise to a very remarkable phe- nomenon in the succession of spores. Not only may some parasitic fungi form different kinds of spores but these spores may be formed on widely different plants. The wheat rusts furnish us with the most familiar examples. The spring spores are formed on barberry or on buckthorn, or on some other plant, according to the kind of rust, while the summer and winter spores are formed on grasses. If one sows spring spores on barberry they will not develop but they must be con- veyed to a grass plant before infection takes place. In a simi- lar manner, when the winter spores germinate, the little spores which are produced on the germ threads must be borne to a barberry or buckthorn leaf before they can cause infection. Spore distribution. Just as the seed plants utilize many agencies for the purpose of distributing their seeds over as wide an area as possible, just so do fungi utilize the same agen- cies for the dissemination of their spores. The fungi in gen- eral may be said to be very prodigal of their spores, so that these are produced usually in great numbers. This may be accounted for in the peculiar requirements of the spore for ger- mination and for further development. Hundreds or thou- sands usually fail to develop where one or two find suitable conditions and give rise to a mature plant. A mushroom or a puff-ball produces literally millions of spores, yet from the abundance of any given kind we know that very few germinate and come to maturity. Again spores are microscopically small and hence in general cannot contain a great deal of nourish- ment. They cannot therefore withstand unfavorable condi- tions of germination for such protracted periods as can many seeds of seed-bearing plants. Many spores can pass through a very long resting period and are capable of germination at the end of this period, but after germination is begun the spore Minnesota Plant Diseases. 27 cannot usually resist unfavorable conditions ; this is an impor- tant principle commonly made use of in combating fungus diseases. The spraying of fungi is most effective if carried out just after the spores germinate. Under the natural conditions of the sowing of spores, unfavorable dry periods may follow closely on a damp season, in which the spores have just ger- minated, and in this way undoubtedly myriads of spores come to grief. Distribution by water. There is a great group of fungi which always live in the water or, if not actually in the water, in very moist conditions; or, as parasites of seed plants, they pass long periods in the resting condition and revive during very moist seasons, as after a rain or heavy dew. Such fungi have spores, with special mechanisms for dissemination through the water. Each little spore is provided with one or two ex- ceedingly delicate whip-like processes which protrude from the end or side of the spore. These lashes whip about and propel the spore with comparatively great speed through the water, until it finally comes to rest and then germinates into a new plant. In this way potato blight is spread and this disease be- comes epidemic only during very wet seasons. In the so- called white rust which so commonly attacks almost, if not all, of the plants of the mustard family, an enormous number of spores is found in white rust-like patches which give the com- mon name to the fungus. These spores are formed in chains and when ripe are blown about by the wind, and are thus borne to the surface of other plants. Here they remain until very moist weather brings about their further development. They then divide up internally into numerous little swimming spores provided, as in the fish and water molds, with propelling lashes, and the chances of infection of the host plant leaves by these swimming spores are thereby many times increased. The white rust therefore uses both the wind and water in the dissemina- tion of its spores. Distribution by wind. The great majority of fungi utilize the wind as an agent for carrying spores. The spores of rusts and smuts are shaken out into the wind by the movement of the plants on which they grow. Their position is of advantage just as is the elevated position of the wind-distributed seeds 28 Minnesota Plant Diseases. and fruits — their radius of distribution is proportionately in- creased by increase of height from ground. Rust spores can be blown for great distances and still retain their power to in- fect plants. In this connection one sees in the structure of these spores a certain adaptation which assists in the wind sowing. The food material packed up in the spore is usually oily and is therefore light in weight. The spore-coat, more- over, has often spiny projections which enable the spore to ad- here to objects with which it comes in contact. Moreover, the summer spores of rusts are often formed continuously for a long period, — throughout the summer, — that is to say, the fungus scatters its chances over a long period rather than con- centrate the production into one effort. The mildews are like- wise parasites with a similar habit of spore distribution. The mushrooms and their allies have learned to use the wind in sowing their spores. The stalked, unbrella-like, fruiting body raises the spores into the air and at maturity sheds them where the wind can take them up. Many shelf fungi on the trunks of trees have acquired especially elevated positions. Such fungi can be said to concentrate their efforts upon the produc- tion of an enormous number of spores for distribution in a comparatively short time and a favorable period is of course sought for this effort. The spores of mushrooms are in gen- eral smooth-coated, as they usually come to the ground before they germinate and require no special means of attachment. Puff-balls also form myriads of spores but do not shed them all at once or in such a short time. Gusts of winds, or a jar by some falling object, may force out little clouds or puffs of spores and such a puffing goes on intermittently for a long period. Distribution by insects. Again some fungi have learned to use insects as an aid in spore distribution. A very effective de- vice has been invented by the fungus which forms ergot of rye. Previous to the formation of the storage organ known as the ergot, the fungus forms a soft mass of much branched threads in the young grain and from these are formed summer spores. These are accompanied by an attractive sugary solution which is luring to insects and with this sugar food the latter carry off the spores, sowing them on other flowers and thus rapidly Minnesota Plant Diseases. 29 spreading the disease. The early spring spores of rusts are often accompanied by structures exuding sweet fluids that are attractive to insects and may be materially beneficial in the sow- ing of spores. There is a certain group of fungi, often known as the honey-dew fungi, which grow chiefly on the leaves of higher plants. They are not parasites but live on insect secre- tions and excreta which are deposited upon the leaves of plants. In this rich pabulum the fungi grow luxuriantly and often form very black sooty coats on the leaves. Such fungi are often specialized to the secretions of certain specific insect forms. A very curious device has been developed among the so-called birds-nests fungi — a device which has to do with the utilization of insects for the spreading of spores. The fruiting FIG. 12. — A carrion fungus. The black head at the top of the fruiting body (lying on the leaf) is covered with a sticky solution in which spores are found. Insects, at- tracted by the odor, carry off this solution and thus scatter the spores. Original. body is beaker-shaped and in the little beaker are tiny flattened egg-like bodies, in reality closed cases, the interior of which contains numerous spores. The "eggs-stalks" become gelat- inous and very elastic when wetted and can be pulled out to a comparatively enormous length. These stalks probably serve to attach the "eggs" to insects' legs and later, becoming en- tangled in twigs or leaves, fasten the "eggs" to these objects. Germination of the spores follows immediately under favorable conditions. Undoubted and remarkable examples of insect aid to spore sowing occurs in the so-called carrion fungi. Here the spores are found in a sticky, usually brownish mass, which is at matu- io Minnesota Plant Diseases. »j rity very qiuckly elevated by a sponge-like stalk to a conspicu- ous height. The spore-mass contains substances that emit a very strong odor as of carrion; hence the common name of these plants. This odor is very attractive to many insects and apparently the spore mass contains abundant food material for it very soon disappears as a result of the numerous visits of flies and other insects. In some forms of these carrion fungi pure white veil-like or lace-like mantles — in appearance much like a large-meshed Wels- kach rrmntle — are produced. j Certain tropical forms, more- / — *\ > £ .ILp — iJf^WM over, add a phosphorescence to these mantles so that they at- tract nocturnal insects, and such FIG. 13. — A birds-nest fungus. To the r . , left are unopened fruiting bodies; forms Open USUally at Or JUSt DC- to the right a section of the same; r < < /^ . 11- the eggs are chambers, carrying fore dUSK. Certain molds spores, and the chamber stalks be- • .1 i /r r i r . come sticky when moist and prob- it the bodlCS Of larvae Ot ably catch in the legs of insects and i:,™^ t^aracifir-alKr rm tVipm An are thus distributed. After Engier living parasiticaiiy on tnem. /\n insect thus infected may carry the fungus to a considerable distance and after death numerous spores will be formed which may infect new larvae. The silk- worm is often preyed upon by these fungi. Distribution by other animals. Vertebrate animals are also occasionally agents of spore distribution. Squirrels often feed on certain mushrooms thereby carrying the spores off into their holes. These fungi are the so-called wound parasites which start life as saprophytes in the dead heart-wood of trees and finally grow out into the sap-wood and kill the tree. In the well-protected shelter of such squirrel holes a wound para- site can get a good start. Rabbits and other burrowing ani- mals often brush up against the fungus fruiting bodies of root- inhabiting forms and carry the spores in their furry coats. Truffles are probably distributed by those animals which feed on them. There is a very large class of fungi which inhabit the dung of certain animals. Such fungi often grow from spores which have passed through the alimentary canals of these animals. The near relatives of the shaggy-mane mush- room are good examples of these fungi. The common com- mercial mushroom also regularly inhabits dung and is there- Minnesota Plant Diseases. ^>i \j :ore raised in caves from beds of manure. Many molds and any black knot allies are also constantly found upon dung, nimals are thus very potent factors in the distribution of the spores of such fungi. Woodpeckers play the same role as do squirrels, for they open holes in the bark of trees by which fungi gain entrance to a tree and boring insects are similar abettors in the attack of wound parasites. Man is an important agent in spore distribution. In all of his commercial transactions, such as shipments of grains, introduction of plants and moving of commodities, fungi of many kinds may be introduced and spread over vast areas. The mallow rust furnishes a good example. This rust was in- troduced from South America less than twenty-five years ago and has since spread over nearly the whole world, becoming a great destroyer of many kinds of plants of the mallow family. The spores of many fungi lurk on the seeds of other plant parts and develop with the advent of favorable conditions. Smut spores are very good examples of such fungi for they often attach themselves to grains of grasses and when the grain germinates attain conditions favorable for their germi- nation. This, at the same time, is precisely the best period for the infection of the grain-plant. Fungus spores or mycelia may be present in bulbs or underground parts of plants which are transported from one place to another and thus are spread over wider areas. Explosive apparatus. In addition to these external factors of wind, insects, etc., some fungi have developed special meth- ods of their own for hurling out spores so that these shall be scattered over larger areas or may better be caught by the wind. The cup fungi have one such device. Here the spores are formed in long cylindrical sacs. These sacs have lids at the apex and when ripe throw off the lids arid spurt out the spores, together with a little drop of fluid material. Often numerous sacs blow off at once so that one sees little clouds of spores arise from the cup. The little mold fungus which causes fly cholera has also a shooting device to thrust off its spores. Each little spore is formed on the end of a thread and is finally snapped off by the protusion of the wall just under- neath the spore. One sees these spores as a little halo around 32 Minnesota Plant Diseases. the fly on panes of window glass in the autumn. A very com- mon dung-inhabiting mold has also an explosive apparatus. FIG. 14.— Various explosive apparatuses for distributing spores. 1. Sac fungus— spores are blown out of the sac when the lid is also blown out. 2. A black mold — the whole top of the spore case with spores is blown off; on right unopened case — on left, case is being blown off. 3. Sphere-throwing puff-ball — showing a longitudinal section with the spore mass ready to be thrown out. 4. The spore mass is ejected by the inversion of the fruiting-body coats. 5. The fly cholera fungus (an insect mold). To the right a spore has been snapped off with a small surrounding mass of sticky fluid which serves to fasten the spore to another insect. 1, after Engler and Prantl; 2, 3, 4 and 5, after Zopf. This fungus forms numerous spores in a case on the end of a fungus thread. The thread just beneath is much swollen and under pressure, until at the ripening of the spores the whole Minnesota Plant Diseases, 33 mass of the latter breaks away and is shot off with considera- ble force. One of the most interesting devices is that found in the ball-throwing fungus. This is a very tiny puff-ball, little larger than a pin head. The spores are not released in a pow- der as is usual in the puff-balls, but cling together in a ball-like mass. The outer coats of the puff-ball burst open in star- shaped fashion and the inner coats suddenly invert, throwing the ball a yard or more into the air, reminding one of the simi- lar methods which certain seed plants, as the common touch- me-not, utilize to cast their seeds abroad. Spore resistance. Just as one finds great diversity in the form and method of production of fungus spores, so also may one find great differences in their powers of resistance. The presence of moisture is often a crucial factor in determining the life of a spore. The spores of many of the algal-fungi, most of which are aquatic in habit, cannot endure a dry atmos- phere for any considerable length of time. This is particularly true of the swimming spores, which are peculiarly adapted to the water habit. \Yhen such spores are dried they lose their power of germination — they are dead. The great majority of fungus spores can, however, endure desiccation with perfect impunity. Such spores as smut spores have been known to retain their vitality for eight years or more in an air-dried con- dition. The spores of the ordinary green molds are also capa- ble of living in dry atmospheres for a very long time. That the atmosphere of an ordinary room contains many such spores in full vigor of life can readily be demonstrated by exposing nutri- ent gelatine to the air, when colonies of green or blue molds will be produced in a few days. Such spores are always, after their maturity, ready for germination. Moreover, the air-dried spores of fungi are in general capa- ble of resisting high and low temperatures, much more so than spores in moist conditions. Blue mold spores can survive dry temperatures of several degrees above the boiling point of wa- ter. But under moist conditions they never survive this tem- perature; in fact, they succumb at temperatures considerably below it. The common treatment for smuts is based on this fact, for smut spores perish in water considerably below boiling water temperature. On the other hand, dry spores can endure 34 Minnesota Plant Diseases. very much lower temperatures. Very many spores of our fungi must be able to endure forty degrees below zero Fahr. to pass the winter. In fact many can undergo still lower temper- atures and survive. Conditions of spore germination. When a spore is placed- under proper conditions of moisture, temperature and of other factors, it germinates, i. e., grows out into a fine thread which, if conditions remain favorable, develops directly into the fun- gus mycelium. By far the largest majority of fungus spores are capable of germination as soon as they are ripe, provided, of course, that such external conditions as light, moisture, etc., are favorable. Many so-called rest- ing spores are forced to undergo a cer- tain resting period after maturity be- fore they can germi- FIG. 15.— A caterpillar-fungus (Cordyceps) spore. A nate- OUCll SpOrCS germinating spore at different successive stages of are DTOVlded With several hours anart. The small resnltincr invrplinm is seen below. Highly magnified. By the author. COatS for tection. This resting period is often connected with the suc- cession of seasons. For instance most of the rust winter spores germinate best in the following spring and cannot be 4made to germinate before that time. Moreover, they retain but a decreasing vitality as the following summer passes, and are usually incapable of growth in the fall. Such spores are adapted closely to the seasons. Not only resting spores but other non-resting spores may also evince such conditions. Rust summer spores are generally incapable of germination after the summer in which they are formed, though some are probably capable of surviving the winter in vigorous condition. Such adaptations are of course especially bound up in the pe- culiar habits of the fungus. Chapter III. Fungi* Fungus Life Methods, Jff Parasitism and saprophytism. \Ye have already seen how fungi have adopted two methods of nutrition, the parasitic and the saprophytic. It may now be pointed out that there is asso- ciated with these methods of nutrition a further difference, viz. : that of reaction to certain impulses. When a certain parasite comes into close contact with a suitable host plant, it is at- tracted or reacted upon by that plant. In other words, it re- ceives an impulse from that plant which results in certain pecul- iarities of growth, e. g., the sending out of sucker threads or organs, and the final result is the parasitic mode of nutrition. The saprophyte cannot respond to this impulse, no matter how closely its threads may be associated with another plant. It has not learned to respond and so is forced to obtain nutriment in other ways, i. e., in the saprophytic mode. Some plants, however, seem to have partially or imperfectly learned to avail themselves of the parasitic habit, while during the greater part of their lives they are true saprophytes. That is to say, at times in their development they may become parasitic, though they are nominally saprophytic. Such are known as half- saprophytes. Some of the blue molds and especially the wound parasites of trees furnish good examples. Again there are cer- tain fungi which are for the greater part of'their lives parasites, but which are capable of passing, even for a considerable period of time, to a saprophytic habit. Some smuts are able to do this. Such plants are known as half-parasites. True sapro- phytes are those whose whole life is saprophytic, e. g., most mushrooms ; while a true parasite draws nourishment from its host plant throughout the life of the latter. Of true parasites the rusts furnish excellent examples. Saprophytes. True saprophytes cannot in any way obtain their nutriment directly from living cells. But since, on account ?6 Minnesota Plant Diseases. \j of lack of leaf-green, they are unable to manufacture starch for themselves they are forced to depend on the products of other plants or animals. Such elaborated food stuff is found in many different forms both in animal and plant remains. Saprophytes which are adapted to growth on special substances often re- quire such materials both for development of the mycelium and also for the germination of spores. The following are the more common habits of saprophytes : The yeast habit. The yeast are fungi which grow luxuri- antly in sugar solutions of one kind or another. In nature they occur, for instance, on the ripe berries of grapes, especially where a berry has broken open and the sugary juice exudes. In this juice the yeast plant thrives. Again in the slimy fluxes of tree trunks, yeasts often grow well. The yeast plant is microscopic in size and propagates with great speed. This speed is often facilitated by the fluid condition of the medium in which the yeast is placed, because the new plants when bud- ded off from the old can easily separate. This is not true of yeast growing in solid starch paste. The yeast usually exerts a peculiar effect upon the medium in which it lives. It exudes at the surface of its cells a chemical substance known as a fer- ment and this substance has the power of splitting up the sugar into two substances, carbonic acid gas, which escapes as tiny bubbles, and alcohol, which remains in the solution. The escape of these bubbles is the well known effect which is pro- duced in fermentation, though not all yeasts cause fermenta- tion. Preserved fruits sometimes "work," gas bubbles arising to the surface. Such may be caused by yeast plants which were allowed to get into the preserves before sealing. Two great industries are founded upon this fermenting power of yeasts. The raising of dough in bread-making is caused by the produc- tion of gas bubbles in the action of growing yeast plants upon sugary solutions, and thus bread-making is dependent upon this process. The second is the process of brewing. The abil- ity of yeast to break up sugars into alcohol and carbonic acid gas is again utilized, but the alcohol is here the chief object of the employment of the yeast. Water-mold habit. Almost all water molds and fish molds live in a submerged condition. Many of the fish molds are Minnesota Plant Diseases. 37 half-saprophytes, since they are capable of attacking living fish or other water animals. As saprophytes, however, the water molds obtain their nourishment from the water in which they are continuously bathed and in which organic food stuff is found in solution. In stagnant pools or ponds they may be particularly abundant. They are often sensitive to the amount of acid in the water, preferring very slightly acid water. Such plants have their food material easily accessible, absorbing it at all points of the mycelium. Dung-dwelling habit. Very many fungi are constantly found on the dung of certain animals. Particular fungi are often to be met with only on the dung of certain species of animals and on the other hand some are almost constantly to FIG. 16.— A dung-dwelling fungus (Pilobolus) of the -black mold group, on horse dung. The threads, bearing spore-cases, are seen pointing in parallel directions. Photograph by F. K. Butters. be found on the dung of these animals if placed under proper conditions. For instance, certain molds grow on fresh horse dung and almost without exception one will find this fungus if the horse dung is placed under favorable conditions of moisture and heat. There are two ways in which the fungus spores get into the dung of animals. They may fall on the dung from the air or they may be deposited with the dung, having previously passed through the alimentary canal. In the latter case they are of course taken in with the food of * 38 Minnesota Plant Diseases. the animal. Many of the latter fungi have so become adapted to this passage through the canal that they require the higher temperature and the previous action of the digestive fluids of certain animals before they will germinate. Such are some of the little black "burnt-wood" fungi which always appear on horse dung when the latter is allowed to remain for several weeks under a bell jar in moist conditions. Besides these burnt wood fungi, the common inhab- itants of the dung of our ordi- nary herb-eating animals are members of the mushroom group, the molds and the cup fungi. The specialization of many forms to the dung of cer- tain species of animals is, of course, explained in the prefer- FIG. 17.— The same fungus as in Fig. r « . . P . 16, greatly enlarged. The spore case CllCC OI the .ailimal tor Certain has a svringe-bulb thread-end, below, r i , i • r 1 • i which "throws off the spore mass. foods, the remains Ol which 111 its%°ores°n MfaSpLtograp^lb" °v. the animal dung are most favora- K- Butters- b!e for the fungus. Earth-dwelling habit. On the forest floor or on the ground, in fields, from the thaw of early spring until snow flies in fall, one sees fungi of one sort or another. Such fungi appear to take their substance from the soil since their mycelium is branched and scattered in the earth. However, if these fungi were removed and placed in pure sand where no plant or ani- mal remains were present, or where no substances had been leached out of dead wood, leaves or roots, and diffused through the soil, they would he utterly unable to develop. That is to say, they are unable to live in plant-free or animal-free soil, and so-called earth-inhabiting fungi in reality draw their nourish- ment from substances deposited in the soil or in solutions in the soil water. It is very noticeable that one finds numerous fungi in the neighborhood of old, partially decayed stumps or tree trunks, where bits of the wood have been scattered about and where the water has long been soaking through the wood. The forest floor is of course usually a humus soil, one which has been built up for inches, or even feet, by the deposit of Minnesota Plant Diseases. 39 plant debris from year to year. Often apparently earth-inhabit- ing fungi can be traced back to their attachment to wood lying buried in the soil, and many plants which may apparently live both on the soil and on the wood belong to this category. FIG. IS.— An earth-dwelling fungus (Lepiota procera) of the gill fungi. Original. Among the earth-inhabiting fungi the mushroom group is per- haps most prominent, but a host of other fungi have a similar habit. Club fungi, many pore fungi, puff balls, carrion fungi, cup fungi, and saddle fungi are found among the commoner forms. Minnesota Plant Diseases, Wood-dwelling habit. A great host of saprophytic fungi grow upon wood — on sawed timber, fallen logs and on the ex- posed heart wood of living trees. They constitute the great timber diseases — the chief agents of the rot of wood. Railroad ties, mine timbers, house foundation timbers, in fact, wood, wherever it is placed in continuously moist, dark places, quickly undergoes a rotting which is caused by these fungi. The wood of all our trees is subject to the attack of some of these fungi, but one kind of fungus is often confined to one kind of tree timber. For instance, the birch pore fungus is found only on birches. As a general rule, these fungi are not able to live in the bark of trees, hence they can gain entrance to the wood of living trees only through wounds in the bark. When once such an entrance has been obtained, the fungus remains in the heart- wood — which is of course dead even in healthy trees — and sets up a decay which may finally cause the tree to become hollow. Such a hollow tree may live for years, since the attacking fungi may be unable to injure the sap wood in which the living cells are found. Wood-inhabit- ing fungi obtain their nourish- ment from the wood in which the mycelium is buried. The "woody" character of wood is largely given to it by a substance known as lignin. The timber saprophyte is able to secrete a chemical which can break down this lignin just as the ferment of the yeast cell breaks down sugar. When the lignin is broken down the wood no longer gives the characteristic chemical tests for lignin. The wood has then been converted into "punk," is brittle and soft and crumbles readily. This action of the fungus is in '- ••" all probability often aided by the FIG. 19.— A wood-dwelling fungus (Dal- , . - dinia vernicosa) on a dead stick of aCtlOll Ot bacteria. Wound Sap- wood. This is a burnt-wood fungus. ropllvtes ga}n entrance tO the Original. Minnesota Plant Diseases. 41 heart-wood through a wound in the bark but never attack the sap wood. Some half-saprophytes are capable of attacking the sapwood after an established saprophytic life — thus becoming parasitic in habit. Such fungi are known as wound parasites. They live most of their lives as saprophytes and are capable of living for an indefinite time as such. The wound parasites are dangerous enemies to forest and shade trees. The injuries and wounds through which fungi gain entrance to a living tree may be caused in numerous ways which will be more fully discussed later. Storms, hail, insects and rodents are among the more common agencies. Leaf-dwelling habit. There is a great host of very minute fungi found on dead leaves, while the latter are still on the tree or after they have fallen. For the most part they are "burnt wood" fungi but one often finds among them small fungi of the mushroom group. In fact, most of those fungi found on the leaf mold of our forest floor are in reality leaf saprophytes. The number of such plants is very large and includes fungi of very different kinds. Most conspicuous, perhaps, are the fleshy fungi of the mushroom group which, on the undisturbed floor of the hard-wood forests in the northern part of the state, often occur in astonishing abundance. The burnt wood fungi are also very abundant. The leaf saprophytes, as well as the wood saprophytes, are of great importance in nature's economy, for they are the agents through which the dead plant structures are gradually disintegrated or broken down until finally the constituents are again mingled with those of the soil and air. The substances are actually burned by this process until they are reduced to soil and air constituents. If this fungus and bacterial disinte- gration of wood and leaves were suddenly to cease all over the world the earth's surface would quickly be covered with the debris of leaf-green plants and its physiognomy would be vastly changed. Many of the plants of this day would require impor- tant alterations in their habits and form to survive such a change, as they would at present be unable to exist among the fast accumulating debris. Plants of low stature on the forest floor would probably succumb first and if one imagines the process to continue indefinitely only the taller plants would 42 Minnesota Plant Diseases. survive. These saprophytes are therefore of great economic importance in two ways. In man's narrower economy they are directly injurious in the enormous losses sustained in the decay of woods and timbers. In the broader economy of nature they are of inestimable value for they are the garbage- destroyers which keep down the accumulation of plant debris. As such their use vastly outweighs those effects detrimental to man's interest. Bees-nest-dwelling habit and others. Certain fungi, whose near relatives are the blue molds, are often found on nests of bees and wasps. They have learned to utilize for their nourish- ment the material of which the nest is made and so well have they learned this method that they are unable to thrive on any other material. One therefore finds certain fungi confined to such material. Other fungi also related to the blue molds are found on horn. They are able to produce a horn-destroy- ing substance which makes the horn material available for the fungus food. One finds such fungi on old cattle horns, or horses' hoofs, and it is only on such substances that they are found. Again, certain fungi occur on bones and still others on feathers. One of the most common of the feather-inhabit- ing fungi is also a blue mold relative. Fungus-dwelling habit. A very common habit among fungi is that of living on other fungi. This is especially the case among those molds which live on plants of the mushroom group. A mushroom placed in a closed moist chamber will soon be covered with mold-growths of various kinds. These molds are for the most part truly saprophytic, though some are capable of parasitism during a part of their life history. Honey-dew-dwelling habit. There is a great group oi fungi which are known as "honey-dew" fungi and for the most part belong to the ''burnt wood" groups. They are true sapro- phytes and live on the excretions and secretions deposited by various insects upon the surfaces of leaves and twigs. They often show an exact selection for the secretion of certain kinds of insects. A fungus of spongy appearance, for instance, al- ways appears on the woolly aphis secretions. After the death of the insect the dead remains of the body become incorporated with the secretions and the whole forms a mass in which the Minnesota Plant Diseases. 43 fungus thrives. The mycelium of such honey-dew fungi is usu- ally black in color and looks like partially burnt wood. These fungi are usually true saprophytes and do not attack the living leaves or plant parts on which they develop. They may, how- ever, grow in such abundance on the surface of the leaves that they cut out the light and hence injure the plant by prohibiting the leaf in its starch-making function. The secretions of in- sects, especially when the latter are abundant, are often evenly distributed over leaf surfaces and hence the fungus may be- come very evenly and abundantly distributed over the foliage. Food-mold habit. It is the common experience of every housewife that bread and cake, and starchy material in general, is subject to molding. Such molding is due to the presence of certain fungi known as black or bread molds. They develop on all kinds of starch foods and especially where these are kept moist, as often happens in improperly ventilated bread boxes. Such fungi will commonly grow in sugar solutions. The molds of preserves are also common enemies of the housewife. These are for the most part fungi of the blue or green mold group. When fruit is preserved in jars spores of such molds are intro- duced with the fruit and those near the lid have access to the included air or to air which leaks in through imperfectly fitting covers. These spores develop into the blue or green mold plants and produce the scum which is so often found under the jar covers. When paraffin is poured on preserves it forms a close-fitting, air-tight cover and does not allow any molds to develop. It is well known how cheese when allowed to remain under moist conditions for any length of time will produce, especially on the rind surface, green patches of mold which, unless removed, increase in size until they cover the whole cheese. This mold is a saprophytic fungus and the green color is due to the millions of spores produced on much-branched threads. Green molds are purposely cultivated in certain kinds of cheese to which they impart peculiar flavors. "Mildew" of clothes. When moist clothes are left in closed, badly ventilated receptacles for any length of time they "mil- dew" or get moldy. This condition is due to the growth of fungi which feed on the cotton or wool fibers. It is only under moist and undisturbed conditions that such will grow. An air- 44 Minnesota Plant Diseases. ing dries out the cloth and the fungus perishes. Moldy clothes have usually lost their firmness because the fibers have been partially disintegrated and weakened by the fungus. Egg-inhabiting fungi. Not all rotting of eggs is caused by fungi, as bacteria are chiefly responsible for these processes. Mold fungi, however, do occasionally penetrate, especially through the cracks in the shells, and live saprophytically upon the albumen. The latter makes an excellent nutrient material and the fungus usually thrives here though it cannot form any spores unless air is admitted. The keeping of eggs in lime or in cold storage serves the same purpose — the prevention of the development of fungi and bacteria. Half-saprophytes. Intermediate between pure saprophytes and pure parasites are those fungi which can live under either conditions of life. Some are, however, typically saprophytes and are usually found growing under saprophytic conditions, but are capable of parasitic life under other conditions. As a rule, such fungi do not show any great specialization or exact selection in their parasitism. They are not confined in their parasitic life to certain specific kinds of host plants but often attack plants of widely related groups. Ripe rots of fruits. Many of the fruit rots are due to fungi of this class. Some of the green molds and also of the bread molds are able to penetrate the thin -skin of some fruits and attack the living cells within in the manner of a parasite. In the killed portions the fungus continues to live as a saprophyte. The living substance in most fruits is at the time of ripeness practically dormant and contains a great deal of food material, both of which conditions serve to make it easier for those fungi, which have not yet learned thoroughly, but only in an amateur- ish way, the parasitic life, to obtain nourishment. The low vital- ity of the fruit-cell protoplasm is insufficient to ward off the at- tack and the large amount of nourishment is an alluring reward. Hence these molds may live for a short time as parasites and then continue their saprophytic life. In fruits a great deal of sugar is stored up and this furnishes the nutrition. The fungus gains entrance through thin-skinned fruits or through cracks in the skins. Those with thick skins are capable of warding off such fungi. Bruising or crushing of berries or fruits may not Minnesota Plant Diseases. 45 only injure them so that the fungus can gain entrance, but ex- uding juices will often furnish nutrition where the fungus can build up a strong mycelium from which the attack upon the uninjured parts may be better carried on. Damping-off fungi. Another half-saprophytic habit is that of the damping-off fungi. These fungi are usually found under very moist conditions and feed upon plant and animal debris in the water. One of the most common of these fungi (Pythi- um debaryanum) requires a very considerable amount of water for its development. When it comes into contact with seed- lings, especially of the mustard family, it is capable of attacking the young plant at about the surface of the ground and kills the tissues. The plant falls over and dies. In this way whole beds of seedlings may be destroyed in a few days. This fungus is never able to attack old plants. The weakness of the seed- lings lies in the fact that the living substance is not yet pro- tected by thick coats of cork and cuticle as it is in the older plants. When the seedlings have been killed, the damping-off fungus continues to live as a saprophyte. The fungus is not a highly proficient professional in its parasitism for two reasons : First, just as do the mold fruit rots, it exercises no particular selection for special kinds of hosts, but will attack almost any plant in the seedling stage ; and, second, it kills its host as soon as it penetrates, thus preventing any further service which the host might pay to its parasite. Rusts and smuts, as we shall see later, are much more proficient in this habit of life than is the damping-off fungus. Wound parasites. Perhaps the most important of all half- saprophytes are those which have already been mentioned un- der wood-inhabiting fungi as wound parasites. These fungi are usually found on dead wood. The bark of trees ordinarily refuses to them entrance to the tree trunk, since the fungus threads are incapable of forcing their way through layers of cork. When, however, a wound occurs which lays bare the wood, this difficulty is overcome and the fungus thrives in the heart-wood. After building up considerable mycelial strength in its saprophytic life it proceeds to attack the growing zone of the trunk, i. e., where the sap wood joins the bark and where the living substance is protected by very thin walls. The host Minnesota Plant Diseases. FIG. 20. — A wound parasite (young specimen of Pleurotus ulmarius). The fruiting bodies are formed in a knot-hole of an unpruned tree. Original. Minnesota Plant Diseases. 47 is thus slowly killed and the fungus continues to live on in its saprophytic way. The wounds, through which these fungi penetrate, may be caused in many ways : the breaking of branches in storms, or the wounds by falling trees, the rubbing together of trees swayed by the wind ; injury by cattle and deer ; lightning strokes ; frost cracks ; hailstones, sun scalds, holes of woodpeckers, squirrels, boring insects ; injury to roots by burrowing animals. Moreover, man himself is responsible for many such opportunities for wound parasites, chief among which are the wounds of shade and orchard trees in pruning. Such wounds should be covered with tar or some other sub- stance which will prevent the development of the fungus myce- lium. Of the wood parasites by far the greater number are allies of the mushroom group. Gill fungi and pore fungi and a few burnt-wood fungi are also found in this class. The best known is the common fall- or honey-mushroom which occurs in clus- ters at the bases of stumps and trees in the autumn. Many of the very common "shelf fungi" are also in this class. Not ail half-saprophytes are dependent upon wounds for their entrance to the tree trunk. A few such, as the honey-mushroom, may gain entrance by attacking the smaller roots with a shoestring- like strand composed of thousands of threads. The latter pene- trate the bark to the growing layer just beneath. They then enter upon a parasitic life and make their way up through the roots to the stem. In this way the fungus can proceed from one living tree to another and cause epidemics. Chapter IV. Fungi* Plant Partnerships* Parasitism* Jff Equal partnerships of plants. Plants often live in very inti- mate relationship with each other. vSometimes this intimacy works out to the injury of one and to the benefit of the other. It may result in benefit to both partners or in what may be called an equal partnership of plants. When two plants find such an intimacy beneficial they may learn to modify their FIG. 21.— A lichen. A plant with equal partnership of fungus and alga. After Atkinson. habits and even their structure in such a way that both may re- linquish the fulfillment of some duties and will depend on the partner for the accomplishment of that work. In this way the Minnesota Plant Diseases. 49 two plants may work as one individual, one unit, though really composed of two plants. Such are the organisms known as lichens, which occur in abundance as flattened crusts on rock surfaces or on the trunks of trees. Each lichen is composed of a fungus and an alga. The algae are for the most part rela- tives of the flower-pot algae, while the fungi are almost all rela- tives of the cup fungi. The little green algal spheres are en- closed in dense wefts of the fungus threads. To the former is assigned the task of starch-making on account of the leaf green, to the latter the task of protection and also of the ab- sorption of mineral salts from the soil. Together the two plants thrive, while, if separated, the fungus at least would perish and the alga would probably not thrive so well. This partnership is therefore of benefit to both plants and the result has been a unifying of two organisms into one. A somewhat similar living together is also encountered among certain plants and animals, e. g., the little wheel animalcule which is always found in the small cup-shaped portions of certain leaves of one of our common liverworts. The cup furnishes a pro- tected harbor for the wheel animal and the plant probably de- rives nitrogenous food from the animal, and thus a living to- gether on equal terms is effected. Unequal partnership — host dominant. The number of equal partnerships among plants is of comparatively rare oc- currence. In a vast majority of cases one partner becomes dominant and the benefits are shared unequally, if not entirely appropriated by the dominant party. In a very few of those very numerous cases when a fungus and a leaf-green plant en- ter an unequal partnership the leaf-green plant is dominant, and what might be termed nutrient parasitism arises. In such cases the fungus derives nourishment from the soil and trans- mits it to the host plant, getting, as far as one can see, no bene- fit in return. In other words, these fungus partners of leaf-- green plants behave much as do the tiny absorbent root hairs which are commonly found on the roots of leaf-green plants. Most of our native orchid plants as well as many foreign mem- bers of the same family possess such a fungus partner. Some of these orchid plants show no external evidence of the pos- session of fungus partners, still retaining their leaf-green in 50 Minnesota Plant Diseases. undiminished quantity. In other cases, where the orchid plant has learned to derive more of its nutrition from the fungus partner, it may economize in its own structure and labor and dispense with some or all of its leaf-green. As a matter of course, the leaf-green organ would also be reduced. Such plants have a yellowish appearance with little or no green color and the leaves are mere bracts. The well-known coral-root orchid is an excellent example of such a plant. The little plant known as Indian-pipe is an even more conspicuous example. It is a little forest-floor plant, whose relatives are members of the blueberry family, and has formed a very effective fungus partnership. So great have its profits become that it has entire- ly dispensed with leaf-green and derives all its nutrition through the fungus in its roots. The leaves consequently are reduced to mere colorless scales and the whole plant has a pure white appearance. There are many other plants, however, which have fungus root-hairs but \vhich have not yet abandoned their leaf-green apparatus for starch-making. They may also pos- sess ordinary root hairs in addition to the fungus. For in- stance, many oak trees, and perhaps most plants of the heath family, possess a subservient fungus root partner. Further in- vestigation will probably show many more plants with this same device, as the list is constantly increasing. Bacteria and bacteria-like plants are also met with as sub- servient root partners of the green plants. Such are the or- ganisms of the root tubercles which are so commonly found on the roots of plants of the pea family. These bacterioids are capable of converting nitrogen, one of the unavailable gaseous constituents of the air, into an available compound, and thus prove of great benefit to the host plant. Often special struc- tures are formed upon the roots by the stimulation of the fun- gus or bacteria and in them these organisms are found. Such structures are usually tubercle-like bodies, as in the clover roots ; or they may be dense, grape-like clusters of tubercles, as are found in the roots of alder trees. In recent years it has been asserted by a French botanist that the well-known potato tubers, which are swellings of the underground stem of our common potato plant, are due to an infection by a certain fungus. This infection is said to be fol- Minnesota Plant Diseases. 51 lowed by the excessive growth of the stem at the infected points. In many of these unequal partnerships we find again the welding together of two organisms into one individual, a phenomenon comparable with that in lichens, but with a differ- ent final result, at least as far as nutrition is concerned. Unequal partnership — fungus dominant. Parasites. An overwhelming majority of the partnerships between fungi and leaf-green plants result in exclusive benefit to the fungus, and this condition is usually designated as parasitism. The host is subservient and the fungus is dominant. It may not be the entire host, though this is so in some cases, that is robbed of nutrition, but special parts only may be attacked and forced to nourish the fungus. From the standpoint of the host plant it may be termed destructive parasitism or simply parasitism in the narrower sense. The destructive effect is the ultimate effect received by the host plant as a unit. The immediate effect of such parasitism may be very local and may be in the nature of a stimulation. Moreover, the living together of a parasite with special parts of its host often produces again, as in the lichen, an essentially new individual composed of the fungus and the host plant-part. Witches'-brooms. Such "individuation" is best shown by the structures known as witches'-brooms. Many of our com- mon trees are attacked by certain fungi, the latter chiefly rusts, whose mycelium becomes confined to a certain w^ell-marked re- gion of the host plant. This part of the host behaves in a peculiar manner. The branches are usually larger than nor- mal, are more numerous, and often, again, profusely branched. The whole mass of branches looks like a little bush growing parasitically on the host. Moreover, the bush usually arises from one point on the host plant and the main branch of the bush, although it may be a lateral branch of the tree, behaves as though it were the leader and grows straight up in the air. Phis brings the bush still more into prominence and demon- the individualistic character of the broom. Such bushes Dwn as witches'-brooms. The branches usually bear leaves which fall early and are often yellowish, having lost some or all of their leaf green. This serves to point out an- other important feature of the broom, viz., that, as an individ- Minnesota Plant Diseases. Cfl 85 Minnesota Plant Diseases. 53 ual, it is living parasitically on the remainder of the host plant. That the broom itself is not injured, but rather stimulated, in its growth is seen by the production of such numerous and large-sized branches. But the ultimate effect upon the whole FIG. 23.— Witches'-broom on balsam fir, caused by a rust fungus (Aecidium elatinum). The branches of the broom are vertical instead of horizontal, as are the normal, un- diseased branches in the right of the picture. Original. plant is injurious because the normal balance of nutrition and work has been interfered with for the rapid production of a group of larger but worthless branches. In a word, therefore, the witches'-broom may be described as a bush- or broom-like 54 Minnesota Plant Diseases, individual, formed by the partnership of a fungus and certain branches of the host, and living at least partially as a parasite upon the remainder of the host plant. It behaves as does a par- asitic mistletoe plant and is not unlike it in appearance. Most of the witches'-brooms of Minnesota trees are due to rust fungi. One of the most common is the birds-nest broom upon red FIG. 24. — Witches'-broom on white spruce, caused by a mistletoe (Razoumofskya pusilla). The spruce is badly affected. Numerous brooms are seen below and the whole upper part of the tree is broomed. (See also Fig. 25 and Fig. 101.) Photograph by author. cedars. These brooms occur in great numbers in many parts of the state and look like crows' nests in the distance. The branches are very numerous and the broom stands on a lateral branch like an independent plant. The leaves are not like the Minnesota Plant Diseases. 55 ordinary leaves but are larger and very spiny, and stand out from the branches just as do the leaves on a very young plant of red cedar or in a similar fashion to those of the common juniper. At the bases of the leaves may be found in spring the brown cushions of spores. Another very common broom, espe- cially in the northern part of the state, is that on the balsam fir. This broom is much larger than that of the red cedar and the branches are often very long and wavy and are thicker than their sister unbroomed branches. The leaves are thickish, and are yellowish in color and fall very early, never lasting as long FIG. 25.— An enlarged view of a broom on the spruce shown in figure 24. The distorted bush-like appearance of the broom is very marked. The mistletoe plants can be seen on the smaller branches. (See Fig. 101.) Photograph by author. as the ordinary leaves. It is clear that the broom must derive most if not all of its nourishment from the neighboring parts of the fir tree. Such brooms may become ten feet or more in diameter. The fungus partner of this broom is also a rust fun- gus and the spores are produced in great abundance in late spring or early summer. Another common broom is found on 56 Minnesota Plant Diseases0 cherry trees. Almost any kind of cherry is subject to broom- ing. The broom branches are usually very numerous and the leaves do not acquire the usual regularity of form but are often distorted. This is especially noticeable where the fungus part- ner forms its spores. The latter are produced usually on the lower surfaces of the leaves over which a grayish filmy coat spreads. This fungus belongs to the sac fungi and is a relative of the cup fungi. Although it produces no cups yet the spores and sacs are arranged in a similar fashion. Birch trees some- times carry brooms which are caused by fungi of the same group. Witches'-brooms are not always caused by fungus attacks. Insects are sometimes also able to produce them, but in many cases the origin of the broom is unknown. In the latter category stand the brooms which are sometimes found on pine trees, occasionally attaining a diameter of over ten feet. Other examples of individuation. Witches'-brooms are not the only cases of the building up of a physiological individual from a fungus and a part of its host. Swellings are often pro- duced on pine trunks which are five times the thickness of the adjacent part of the trunk. Such swellings are caused by a parasitic fungus and may be considered again as individuals which are living luxuriantly at the expense of the host tree. Burls on trees are by no means uncommon though their origin from a fungus infection is not always clear. In many cases their origin is unknown. Again, such tubercular swellings as are found on Indian corn, where smut later arises, are in reality favored individualized parts of the corn with a fungus partner. Large galls form in allies of the blueberry plant upon leaves and stem, and these galls are also of fungus origin. A larger number of examples might be cited but enough have been mentioned to illustrate the individuation of fungus with plant parts in a parasitism which is ultimately detrimental to the host plant. In most cases of parasitism of fungi the host plant does not in any way show a stimulation of the affected parts and the absence of any difference in the action of the affected and nor- mal parts indicates a low degree or absence of individuation. It is worthy of mention here, however, that parasitic fungi in general thrive best on healthy plants rather than on weaklings, Minnesota Plant Diseases. 57 though some weak points in the plant organization may be re- sponsible for the successful attack of the parasite, as has been experimentally proven within the last year. In other words, the most successful parasitic fungi are those which can stimulate the affected parts of host plants to extraordinary effort, or at least do not immediately injure those parts. FIG. 26. — "Birds-nest" witches'-broom on red cedar caused by the birds-nest rust fungus (Gymnosporangium nidus-avis). The bush-like broom stands vertical on the horizontal branch of the host. The difference between the diseased and healthy leaves is very marked. The former are very similar to those of the common juniper. Original. Degrees of proficiency in parasitism. The simplest modes of parasitism are undoubtedly to be met with in those half- saprophytes which are just learning the methods of parasites. Some of these have already been described in certain mold fruit- rots. Such a beginner can only obtain its food from living 58 Minnesota Plant Diseases. substance which is in a resting state and which approaches most nearly the condition of dead proteid material. More- over, such protoplasm contains much nutrient material. The fungus kills as soon as it comes into contact. It has not acquired any particular choice for specific kinds of hosts but attacks al- most indiscriminately. The damping-off fungus is another amateur parasite, though it has carried a little farther its ability to kill. It is able to attack vigorously growing parts, as seed- lings, but, like the fruit molds, does not exercise any well- marked preferences in its selection of hosts, i. e., it may attack almost any seedling. The beginnings of such a preference are indicated in the great frequency with which it attacks seedlings of the mustard family. The wound parasites of trees show likewise a low degree of parasitic efficiency. They require a mycelium well established by previous growth in the heart- wood before they can successfully attack the living part of the tree. When, now, we examine the powdery mildews, e. g., the powdery mildew of lilac bushes, we find an improved method of parasitism. The fungus does not noticeably injure the host, though it is of course detrimental to it even when the results are not evident, and in some mildews the results are obviously disastrous to the host. Moreover, the parasite requires special hosts and a given mildew is found only on one kind of host, or only on plants which are very close relatives and so furnish very similar materials. In other words, the mildew is more select in its choice of food than the damping-off fungus, and its method of attack is more complicated and exact in its detail. Now, if one considers the parasitism of the smut fungus, e. g., the smut of corn, one sees again an improvement in para- sitic methods. In the first place the fungus has refined very much its selective power for food and can now only exist as a parasite on corn, and is unable to live on any other plant even of the same family. But when it has once established itself upon its host it does not immediately destroy the attacked portion of the plant, as would the damping-off fungus ; neither is it a passive passenger, as is the mildew ; on the contrary, it stimulates the part of the corn plants on which it lives and causes that part to grow abnormally larger at the expense of Minnesota Plant Diseases. 59 the rest of the plant. Then arise the carbuncle-like swellings of the leaves. If a kernel of the cob is attacked it increases perhaps tenfold in size. During this increase of size the fungus is also gaining strength and keeping pace with its partner plant-part, and when the proper moment has arrived for the formation of its spores it proceeds rapidly and utilizes all the extra food stored up by the swollen host plant-parts and de- stroys the latter rapidly. Such a parasite stimulates its host to unusual activity for a long time and at the same time pre- pares to use to best advantage all of the nutrient material laid up by the host, delaying its destruc- tive effects until the most advanta- geous moment. Sometimes, as in oat smuts, the presence of the fungus is not determinable until harvest-time, when the fungus forms its smutty powder of spores in place of the grain. This is a very efficient meth- od of parasitism but, in some respects at least, the fungi producing grain rusts are even more capable. The smut produces but one kind of spore on its host plant and that is a resting spore for tiding the fungus plant over the winter season. The rust fungus can produce spores from early spring to autumn and is able to do this by forming different kinds of spores at different seasons. Such a rust will produce a spring spore, a summer spore, and in autumn a so-called win- ter spore, the latter having the same function as the spore of the smuts. This continuous production of spores FIG. 27.-oat smut-an accom- js of COursc a very efficient device. plisned parasite. After G. P. Clinton. jn addition to the multiplicity of spores the rust fungi often possess the stimulating powers al- ready mentioned for smuts. Such have also been described in witches'-brooms of red cedar and balsam fir. In the simpler 7 6o Minnesota Plant Diseases. cases of rusts all of the spore forms are found on the same kind of host plant and it is now a well-known fact that the rusts are extreme specialists in the selection of their hosts. So exact has this selction become that certain rusts will attack one grain plant and are unable to attack other even closely related grasses. In this respect they are among the most proficient of all known parasitic fungi. Still further complications may, however, arise. A rust fungus may increase its distribution by selecting in the spring time another earlier plant for a host, and produce upon this plant its spring spores. This migration is the expression of one phase of the education of the most highly educated plant parasites known to botanists of today. In view of these and other accomplishments of these fungi one has little hesitation in pronouncing them the most proficient parasites amongst the fungi. The modes of life of parasitic fungi. In general, there are two methods of life. The fungus may live on the surface or it may live within the tissues of the host plant. The powdery mildew of lilacs lives on the surface of the leaves while the smut of oats lives inside the tis- sues of the oat plant. Those fungi living in the tissues of their host, how- ever, come to the surface when they are about to produce spores. The sur- face-dwelling fungus may derive its nutrition in one of two ways : it may send special threads into the living substance of the host and through these sucker-threads draw nourishment, or may merely attach itself to the surface of the plant and never send threads into the living- substance. It is clear FIG. 28. — An endophytic (internal) mycelium be- tween the cells of a grass grain. (Fungus of Lolium temulentum.) Highly magnified. By the author. Minnesota Plant Diseases. 61 that in the latter case the nutrient material must first pass through the walls of the host plant before it can be taken up by the fungus thread. The interior-dwelling fungi may get their nourishment in several ways. In many, special sucker- threads are sent into the living substance of the plant. In other cases the fungus threads run between the cells of the tis- sues without ever coming into direct contact with the living substance. On the other hand, fungi may gain entrance to the cells and live entirely within them. Such is the common method of many very minute water fungi. The sucker-threads of the various fungi differ considerably in shape and often fur- nish important marks of distinction, since each fungus may FIG. 29. — Infection of a grass leaf by a rust fungus (wheat rust). Above is a summer spore showing germ-tubes. Below is a germ-tube entering through the pore of the leaf and is reaching down in the internal part of the leaf where it soon becomes well established. After Ward. have its own peculiar form of sucker. The simplest are little cylindrical unbranched threads. Again, they may be small tubercular hyphae ; others are branched to form a stubby-fin- gered, hand-like system of threads. In still other cases the suckers may be very much branched and the branches may be coiled up into dense mats entirely filling the cell of the host. Methods of attack. When the spore of a parasitic fungus falls on the leaf of a host, it awaits favorable conditions for fur- ther development. When the moisture and temperature and other conditions are most favorable the spore sends out a 62 Minnesota Plant Diseases. thread which in many cases grows directly to a ventilating pore of the leaf and enters through this pore. In many cases, how- ever, it is able to bore its way through the walls and thus pene- trate to the interior. Special threads may be developed to fasten the germinating spore to the host plant. This is accom- plished by minute disk-like ends similar to little rubber vacuum cups. Abundant hairs on the surface of a host plant, or a very thick cuticle, may lessen the danger to the host of fungus at- tacks. Some fungi select certain periods in the growth of the host during which the latter is less able to ward off the attack. Such is seen in the oat smut and damping-off fungi, which at- tack seedlings, or again in the wounded trees where a fungus gains entrance before the tree has had time to close a wound in the normal manner. Since the selection for a time for attack is in many cases of great importance to the fungus, the latter usually forms its spores to coincide with this favorable time. Fungi which attack the trunks of trees are usually unable to penetrate the bark unless aided by wounds of some sort, but they may occasionally penetrate through the ventilating holes. Mention has already been made of those fungi which require previous preparation for attack, as is the case in many of the wound parasites. The living together with special plant-parts. Parasitic fungi do not usually live together with all parts of their host plants but confine themselves to certain organs, or at least show pref- erence for certain plant-parts. Leaf-inhabiting parasites. Perhaps the most conspicuous and common are those which prefer the partnership with leaves. Most rust fungi are of this class; most mildews, blights, leaf-curls and that great group of imperfectly known fungi which commonly form the so-called leaf spots. The foliage leaf is usually selected by the fungus, though more rarely the scale leaves or floral leaves may also be attacked. Sometimes, as in the leaf-spot, the fungus only inhabits a small portion ; in others it may pervade or cover the whole leaf. The leaf-dwelling parasites are perhaps the most destructive of all fungus parasites, both on account of their number and their effect upon the starch-making machinery of the plant. The ease with which the fungi develop in the leaf-tissues is perhaps Minnesota Plant Diseases. 63 explained by the fact that, on account of the great air-spaces inside of the leaf, the fungus can easily obtain the air gases which are necessary for its development; secondly, that these spaces are always more or less moist on account of the water vapor given off by the leaf tissues ; and, lastly, they are not too highly illuminated by sunlight. The interior of a leaf, therefore, furnishes excellent opportunities for fungus develop- ment and many fungi have availed themselves of these oppor- tunities. Moreover, the fungus can often gain easy entrance through the air pores on the leaf surface. When a leaf-fungus dwelling in the interior is about to produce spores, it forms the latter usually at the surface of the leaf. Sometimes, as in the potato-blight allies, it shoves the spore-bearing threads out through the air pores, but this is not the method in the rusts Here the leaf surface is broken open, splits out, and the interior- ly formed spores reach the air through the split. Of course such an injury, minute though it may be, really injures the leaf by the interference with the leaf control of water vapor. A large number of such wounds, together with the injury by loss of nutrition to the fungi, may cause the death of the leaf. The spores of the fungi usually appear as a powder or cake uncov- ered by the upheaval of the leaf surface tissues. In some few leaf-fungi the spores are formed internally and are only released by the decay of the leaf. Stem-inhabiting parasites. The stems of plants furnish an- other favorite abode for parasitic fungi. In the stems of herb- like plants the fungus problems of entrance and life are not very different from those of the leaf except that the tissues are firmer. Hence we find many rusts capable of living either on the leaves or stems of a given host plant. But in woody plants, as in shrubs and trees, the fungus meets with new difficulties in the nature of a thick layer of bark which must be penetrated before the living part of the stem can be reached. Moreover, the compactness of the tissues and the resultant absence of larger air-spaces do not make the stem such a congenial dwell- ing place as is the leaf. In such woody stems, therefore, we find almost exclusively those fungi which are capable of break- ing down woody tissues and feeding on them. It has already been stated that these fungi must usually depend for entrance 64 Minnesota Plant Diseases. to the stem upon some wound, which will remove the protect- ing cork layer from the wood. Many burnt wood fungi in- habit stems both herbaceous and woody. On the latter are very often found the gill fungi or mushroom allies and the pore fungi. These fungi are in general long-lived, living from year to year on a tree trunk and storing up nourishment in their mycelia. Months and even years of preliminary growth are often required of such fungi before the spore-bearing or- gans are produced. Enormous numbers of spores are then formed and a new crop may be shed every year until the nour- ishment in the tree trunk is exhausted. Root- inhabiting parasites. The root is not as popular a resort for parasitic fungi as either the leaf or the stem, but not a few find a congenial abode in these parts. They have similar difficulties to meet as the stem dwellers and are in fact mostly members of the same groups of fungi. Often the same fungus is capable of growing up into the tree trunk. The spore-bear- ing organs are always found either at the surface of the ground or in air-spaces in the soil, such as in the burrows of rabbits. In certain grass-like plants a smut is found in the roots and causes the formation of swollen pear-shaped bodies. Fruit-inhabiting parasites. A very large group of fungi inhabit the fruits of flowering plants. The fruits, whether they be fleshy, like apples, or hard, like nuts, have always some protective coat, which is a serious obstacle against an invading fungus. Some fruits are better protected than others in this respect and the weaker may prove vulnerable to fungus attacks, e. g., when thin-skinned apples are invaded by mold rots. The smuts, which are commonly found in the grains of grass- plants, have devised an ingenious method for a successful at- tack upon the fruit of the grasses. The fungus gains entrance to the stem of the plant when the latter is in the seedling stage and then keeps pace with the growing plant without appar- ently affecting it at all detrimentally, until the grains are com- mencing to fill. Then the fungus permeates all of the grain tissues, appropriates the food material and forms its smut spores. The ergot .of rye and other grains has still another device for attacking the grass fruit. It does not, as the smut, live in the point of the stem until the fruit is formed, but at- Minnesota Plant Diseases. 65 tacks the grain from without while the latter is still very young. It seems to be able to penetrate the grain coats at this stage and immediately proceeds to convert the grain into storage material, packing it up in the dark-coated storage organ known as the ergot. This is used in the following spring to produce the spore-bearing organs. The fruit-inhabiting fungi include members of almost every group of fungi. Fruit-mold rots, smuts and ergots have already been mentioned. There are many other burnt-wood fungi beside ergot. Plum-pocket fungi, cup fungi and algal fungi are also among the inhabitors of fruits. Anther-inhabiting parasites. Among the smut fungi are to be found forms which have developed very strange habits. One of the most remarkable cases is that of the smut which forms its spores only in the anthers of particular kinds of plants. The latter are members of the pink family. The fungus gains en- trance to the plant before the flower is completely formed and in the young flower it selects for its abode only the stamens, and particularly the pollen-bearing part or anthers. It gives no external evidence of its presence until the flower opens. \Yhen this happens one finds that, in place of pollen, the an- thers give forth a violet dust of smut spores, and few, if any, pollen grains are produced. To the casual observer such flowers appear to throw off purple pollen while other flowers of the same kind of plant give off yellow pollen. The fungus has formed its spores in place of the host's pollen, and when the anthers open they shed the spores. When insects visit these flowers they carry smut spores in place of pollen from plant to plant, thus aiding in the spread of the fungus. These fungi often prove troublesome pests on plants of the pink fami- ly, such as carnations, where the flowers are grown for show plants, because the presence of the fungus cannot be foretold before the opening of the flower, and after the latter event the smut spores discolor the flowers so that they are worthless for the market. It can readily be seen that this fungus has car- ried to a remarkable degree of efficiency its selective power, having learned not only to repress its spore formation until a most favorable moment but also to choose a most advanta- geous special floral part for the spores. Chapter V. Fungi. Parasites on Animals. An account of the parasitic fungi would be incomplete with- out some mention of those fungi which attack animals and cause disease in them. These fungi are becoming more and more of economic importance, especially in their use in com- bating insect invasions on agricultural crops. They are fur- thermore of great interest in the diseases which they cause in man and the lower animals. In general, these fungus parasites belong to the lower or algal fungi, the water molds, bread- mold-allies and insect molds; but not a few are found amongst the higher fungi, e. g., the caterpillar fungus, the green mold, and even yeast-like fungi. Diseases of lower animals. Not even the most lowly groups of animals are exempt from fungus parasites — on the contrary, they seem to suffer to an unjust degree. Those small unicellular animals which usually inhabit the water are often attacked by the simplest of fungi, also unicellular and very minute plants. The fungus finds its way through the wall of the animal cell and draws its nourishment from the animal protoplasm. Sometimes the fungus is exceedingly minute and may confine itself to only a special port'on of the proto- plasm, as do nuclear parasites. Where (as in the Coelenterates) the host animal possesses a protective coat of lime the invading parasite may bore through the lime. The resting stage of these small animal- cules furnishes an especially inviting host, since here the fun- gus meets with less resistance. One parasitic fungus is known to live only on the eggs of the little animals known as wheel ani- malcules. The pin worms are likewise subject to fungus diseases and one often finds an epidemic raging amongst colonies of these little creatures. As these worms are often greenhouse Minnesota Plant Diseases. 67 pests such a fungus may become an efficient aid to the horti- culturist. The method of attack of this fungus is a very un- usual one. The mycelium is built on the principle of a net in which the threads of the fungus form loops or meshes. In these meshes the wiggling pin worm becomes entangled and every effort to free itself usually results in a securer imprison- ment. When the worm is held fast the fungus sends out- threads which penetrate the body of the prisoner and absorb its substance. Amongst the true worms, fungi have been reported on the common earth worm. These fungi belong to the fish or water molds. The little water flea (Daphne) is the host of a very interesting fungus. This fungus is said to be a relative of the yeast fungi which are not, as a rule, parasites, but true saprophytes. The spores of this yeast or yeast-like plant are long, pointed, almost needle-shaped, and when taken into the alimentary canal of the water daphne they penetrate the wall of the canal and get into the body cavity. Here a fight ensues between the white corpuscles and the spores. If the latter con- quer they soon commence to divide in yeast fashion and rapidly use up the nutrition derived from the fluid of the body cavity. The host animal soon becomes sluggish and dies. Later the needle-shaped spores are again set free and may be swallowed by other daphnes. The crabs have also been reported as hosts for fungi, but such occurrences have not been very frequently noted. The parasites in these cases are water or fish molds. Amongst the spiders a black fungus parasite is known. Even upon the clam fungi have been reported, but their parasitic nature has not yet been proven. Shell-boring fungi are often found on the shells of such animals. Diseases of insects. Of all the animals the insects are by far the most popular hosts for parasitic fungi. Most of the fungus parasites attack the insects in their larval stages, when the latter, with worm-like habits, crawl through the soil or in other moist places. Hence the fungi most frequent upon them are forms of the algal fungi which are also typically aquatic in habit, though of course many have learned to live in dry situ- ations. The fungi of insects have certain advantages. In the 68 Minnesota Plant Diseases. body of an insect there is considerable chance for aeration on account of the large number of air-tubes which traverse the insect body. This very probably accounts very largely for the popularity of the insects as fungus hosts. Of these fungi the insect molds are very abundant as is also the "burnt wood'' fungus known as the caterpillar fungus, and these two- groups of fungi are responsible for most of the disease epidemics of insects. Plant lice have been known to suffer from attacks of both of these fungi. The common housefly and its relatives are de- stroyed in enormous numbers every fall by an insect mold causing a disease commonly known as fly cholera. Such flies are seen clinging to window panes or the ceiling or walls of a room, surrounded by a dim circular haze or halo of the fungus spores which have been forcibly snapped off from fungus threads and caught on the glass. Of course most of the spores have been thrown off into the air where they may float about until they come into contact with another fly. The fungus continues to form spores as long as there is available food material in the insect body. When spores alight on an otherwise healthy fly a fungus thread is pro- duced which may make its way through the skin to the inside of the body and there continue to grow. The mycelium soon causes the death of the insect and later comes again to the surface to produce its spores. Other insect molds have been known to attack com- mon house fly relatives. The mosquito may also prove a prey to fungus diseases and attempts have been made to fight it by aiding the spread and dissemination of those par- ticular insect-molds which are parasitic upon it. One of the most remarkable groups of insect parasites are the beetle fungi, relatives, perhaps, of the black fungi. They are found FIG. 30. — Beetle fungi attached to an insect. The black spots at the base are the at- taching organs. Highly magnified. After Thaxter. Minnesota Plant Diseases. 69 on the legs and wing covers of flies and particularly of water beetles. They are highly specialized as to their abode, often occurring constantly on a certain joint of one leg. This defi- niteness of position is explained in the spore distribution, as the plant sexes are often separated, growing on different plants, and the sexual cells of the fungus are brought together dur- ing the breeding acts of the insects. These beetle fungi are not, as far as is at present known, harmful to the insect which they inhabit. In form they are very minute and visible only by the aid of strong lenses. They usually have the shape of little broom brushes and are attached by a blackened disk. The butterflies, particularly in their caterpillar stages, are also common prey for the insect mold. Perhaps more com- monly, however, they are attacked by the fungus known as the caterpillar fungus, a member of the black fungus group. This fungus has learned to produce a variety of spores, each special- ized for a certain purpose. Cylindrical spores are produced upon orange-colored fruiting bodies in the autumn. When a spore falls on a caterpillar it sends out germ-threads which can eat their way through the covering of the caterpillar and enter the body cavity. Here the threads immediately form long nar- row spores which are pinched off into the fluid of the body cavity and can move around easily, thus rapidly spreading the fungus. These spores germinate immediately and more spores are formed. Meanwhile the threads produced by these spores branch profusely and soon permeate all parts of the insect body-cavity and invade the various organs, finally working their way even into the muscle fibers. The caterpillar gradually becomes sluggish and finally dies. After death, the fungus continues to grow and to appropriate the insect substance for food. At fist the threads are very thin and are thus able to work their way with more ease through all parts of the body. As soon, however, as the threads become very numerous they grow thicker and lay up nutrition as storage material in the form of oil and fungus starch. Finally the threads have com- pletely absorbed all of the insect's soft parts, filling the chitin- ous covering, and retain in their densely compacted form, the exact shape of the larva — not only in the external form but in the form of the internal organs. In other words a mummy 70 Minnesota Plant Diseases. and model has been formed ; this mummy contains a great abundance of food material, but no part of the insect can be found in it. The mummy now acts as a storage and resting organ and requires apparently considerable time — months, perhaps — to ripen. Under favorable conditions this mummy will send up an orange-colored club-shaped body, which will again produce the kind of spore which was described at the be- FiG. 31. — Various kinds of caterpillar fungi with fruiting bodies. (Cordyceps militaris, C. stylophora and Isaria sp.) The forms of the caterpillars are preserved by the fungus storage organs and the upright clubs bear the spores. 1 and 2 bear clusters of pinched- off accessory soores; 3 and 4 bear sac- spores in capsules. (See chapter 9.) About natural size. Original. ginning of this account. Under some conditions, however, the mummy can be made to produce a dense growth of threads from its entire surface, so that it looks like a small ball of cotton, and from these threads another kind of spore is formed. These spores are pinched off in great numbers. They have the power of germination and infection of the larva in a way similar to that of the sac spore already described. Caterpillar fungus epidemics are not infrequent and thousands of larva may be Minnesota Plant Diseases. 71 killed in a year. A caterpillar after infection can still crawl some distance before death overtakes it and thus the scattering of the fungus spores is materially aided, Attempts, made at vari- ous times to utilize this fungus to combat grubs, have met with varying success, but its use has not yet become general. Silkworms frequently suffer from these fungi and the silk growers of Europe have lost enormous sums of money through such epidemics. The beetles are very frequently the hosts of parasitic fungi, especially of the so-called "beetle fungi" which have already been mentioned. The caterpillar fungus and the insect molds are also to be found on the beetle as well as upon the dragon flies and their allies. Ants, though not very frequent hosts, have been known to harbor the caterpillar fungus. Diseases of fish and lower vertebrates. If we now consider the vertebrate animals we find also abundant evidence of fun- gus parasitism. One of the most important cases is that of the fishes. Both the mature fish and its eggs may be attacked. FIG. 32. — Dead minnow with fish mold (probably Saprolegnia thuretii). Original. The fungi are the water or fish molds. Thousands of fish are killed off annually by these parasites. They can be seen on any minnow bait, which has died and been kept for several days. A filmy mold gradually covers the whole surface of the minnow. These fish molds are half saprophytes and live ordi- narily upon dead debris in the water. When, however, they come into contact with living fish, they may attack the latter if conditions are favorable. They apparently are unable to Minnesota Plant Diseases. FIG. 33. — A spore-case of fish- mold showing escaping swim- ming spores; each of the spores is provided with two swimming lashes which whip about in the water and propel the spores. Highly magnified. After Zopf. attack healthy fish unless perhaps through the respiratory system, but succeed if the fish are in some way in- jured, for instance at points where the scales have been rubbed off. When once the parasites are established they gradually spread over the body of the fish and ultimately cause its death. The fungus produces an enormous number of spores which are for the most part furnished with whip-like lashes for propelling purposes. Oc- casionally these fish molds cause epi- demics and vast numbers of fishes may then succumb. The occurrence of several such epidemics is known. These fungi are very often the cause of the death of fish in aquaria such as common gold fish. The danger from such fungi can be lessened by keeping the aquaria scrupulously clean so as to furnish little chance for the sapro- phytic existence of the fungus. The infected fish should be removed as soon as possible to prevent the forma- tion of more spores. The injuries of these fungi are not confined to the fish in lakes and streams but are sometimes a cause of great loss in the fish hatcheries where the eggs may be attacked. Some of the bread mold allies are also known as inhabitors of fish eggs. On the Amphibia, the frogs and their relatives, few fungi have been found. In this state mud puppies have been observed, which have been killed by certain fish molds. The fungus appeared on an apparent- ly healthy mud puppy as a thin filmy spot which rapidly grew larger, coa- lescing with other spots until the ani- Minnesota Plant Diseases. 73 mal was completely covered. Meanwhile the puppy gradually grew sluggish and finally died. Soon after death the fungus had formed around the mud puppy's body a dense mass of mold almost an inch thick. All the mud puppies left in the same aquarium were finally killed by this mold. Diseases of birds. Birds are not without their fungus para- sites. However, these parasites are members of a different group of fungi from those inhabiting fishes and amphibians. In the latter the parasites are adapted to aquatic habits while on the birds one finds fungi which have become adapted to aerial life. The birds offer somewhat analogous advantages to fungi which one finds among insects ; that is to say, abun- dant aeration furnished by the bird habit of life. One fungus disease of birds is caused by forms of the green molds which affect particularly the respiratory organs causing inflammation of the affected parts. Almost all classes of birds have been reported as hosts of these parasites. Chickens sometimes suffer from a comb scab which is also of fungus origin. This fungus, when raised on gelatine plates, shows similar life habits to the yeast fungi. In this disease scabs are formed on the comb and the fungus inhabits the scab spots. The same form, or a close relative of it, may attack the crop of the chicken and form a pustule disease. Hens' eggs, as has already been mentioned, are not infrequently attacked by fungi of the green or black mold group and egg rot ensues. Such fungi may, however, be mere saprophytes living on the albumen of the egg. Diseases of lower mammals. There are several diseases of considerable importance among the mammalians. The most serious of these is the disease of cattle known as lumpy jaw. The cause of this disease is apparently a fungus but its position in the classification of fungi is not yet known because its spores have never been observed. It occurs in little nodules which ap- parently multiply very rapidly. It attacks most commonly the jaws and mouth parts of cattle and the diseased animal's head becomes much swollen and presents the lumpy appearance which gives the disease its common name. The results are usually fatal. Infection apparently takes place from the food, particularly from the hay and grain foods, upon which the fun- gus has been found to exist. The fungus is probably intro- 74 Minnesota Plant Diseases. duced in cuts in the mouth made by grass blades when the animal is feeding, and from these points spreads throughout the mouth parts. Inoculation with the nodules results in the typical disease. At times the disease becomes epidemic, prob- ably on account of the prevalence of the fungus in certain food. The same fungus, or one very closely related to it, attacks swine. It is not always confined to the mouth parts. Horses have also been known to suffer from the same disease. In the lungs of rabbits, cats and dogs the spores of green molds may lodge. Under favorable conditions of weak resistance, the spores may germinate and induce inflammation in the sur- rounding parts, causing the formation of tubercular growths in the lung tissues. The disease is known as a mycosis. Such fungus spores injected into the blood of animals may also give rise to mycosis in various organs of the body. The intensity of the disease seems to be proportionate to the number of spores injected or inhaled. This is of course not the cause of ordinary tuberculosis. Bread mold allies are reported as responsible for diseases in rabbits. They gain entrance to the intestine with the food and. produce diseases of the intestinal tract. When injected into the blood the spores may produce diseased conditions in the kidneys and other organs and even in the bone marrow. Death sometimes results from the attack of these molds. An ally of the yeast fungus, and apparently also of the comb scab disease of chickens causes in the throat and mouth parts of young cats and dogs pustules and scabs similar to those produced in throats of children. The fungus is found in the scabs and pustules thus formed. Several other external scab diseases of the skin of animals are produced by these fungi, as are also the bald spots, accompanied by scabs on the exter- nal head and throat parts, often found on cattle and less often on dogs, horses, cats, etc. The latter may be identical with bald spot disease in man. Diseases of man* Skin diseases of man, analogous to those of the lower mammals, are caused by fungi. Ring worm and some bald spots are prominent among these. They are caused by fungi perhaps identical with those of lower mammals, at any rate very similar to these in all their characters. Minnesota Plant Diseases. 75 Cases of lumpy jaw in man, though not very frequent, are well known. The disease is similar in all respects to that pro- duced in cattle. The fungus is similar and the results are usu- ally fatal. Infection takes place in all probability from cuts by splinters or wounds by grass blades, or when a grass blade is drawn through the mouth or grains in the field are sampled by biting. The fungus thus appears to lurk in places similar to those of the fungus of lumpy jaw of cattle. Green mold fungi also cause disease in man. Some dis- eases of the outer and middle ear canal are of this nature. Here the fungus grows as a saprophyte in the ear secretions and by its presence sets up irritation and consequent inflamma- tion. It is doubtful if the fungus in this case is a true parasite. These molds, moreover, when inhaled into the lungs in sufficiently large quantities, may produce lung and bronchial troubles. The latter are often asthma-like in their symptoms. Children are subject to the attack of one of the yeast-like fungi, similar to the comb-scab of chickens and the throat troubles of cats and dogs. As with the last two the in- ternal throat-parts are attacked and scabs and pustules pro- duced in which the fungus is found, giving rise to sore throats. Somewhat similar throat troubles have been produced also in adults by a similar fungus. Contrast of parasitism in plants and animals. A great dif- ference is noticeable between the known number of fungi para- sitic on animals and plants. The former have been estimated as less than two hundred while the latter must now exceed ten or fifteen thousand. This difference can, in part, be accounted for by certain general differences in surroundings. Fungi as a rule require neutral or acid media, while animal tissues are usually alkaline. Plants offer in their tissues more air space and thus furnish more air, which is essential to the growth of fungi. The body temperature is, in all higher animals, above that at which most fungi develop under normal conditions, and finally, the resistance of the white corpuscles of the blood is an important factor. Fungus parasitism on animals is, with per- haps the exception of lumpy jaw, an immediately destructive one, and shows no effect of mutual partnership between fungus and animal parts. 76 Minnesota Plant Diseases. Just as with bacteria, so with fungi, — white blood corpuscles seem to form the garrison guarding against attacks. As soon as the fungus threads enter the tissues, the corpuscles gather around them and the battle begins. Moreover, the corpuscles are often produced in extraordinary numbers in the vicinity of the fungus attack. They may thus exclude air from the fun- gus and so materially hamper its growth. Plants have no such protection and hence suffer more. The fungus may sometimes encrust itself with lime, as in lumpy jaw, perhaps protecting itself in this manner from unfavorable conditions. Chapter VI. Fungi* Parasites of Plants. Jff Effect of parasite on host. We have already seen that para- sitism, in the broader sense, of a fungus on leaf-green plants is always one of two kinds of partnership, equal or unequal, and of the latter either the host or parasite may dominate. Now, equal partnerships are rare, and those unequal associa- tions with dominant hosts are also comparatively few, though science is rapidly adding many new examples to the list already known. The greatest number of partnerships are those in which the parasite is the profit-making partner and the host FIG. 34. — Damping-off of seedlings, caused by a fungus (Pythium debaryanum) which immediately kills the host plant — a low, though effective, type of parasitism. After Atkinson. the loser. It has also been pointed out that different fungi have acquired different degrees of efficiency in obtaining their prof- its, and that highly specialized parasites can influence the host to over-production of food stuffs for the benefit of the former. 78 Minnesota Plant Diseases. Immediate destruction. The immediate destruction of plants or plant parts has been characterized as an amateur method. It is admittedly not as clever a method as is the de- layed destruction preceded by stimulation. But the perform- ance of even such amateur methods can be carried to a high degree of proficiency and that is what many fungi have done. The green-mold fruit-rot effects its parasitism not only accord- ing to amateurish ways, but is a beginner in this work. This is not so with the potato blight, which is an adept at its meth- ods of killing and feeding on the potato plant. There are many special methods to be found among these parasites but they may be brought under these heads : the destroyers of small areas of plants, the destroyers of whole organs, and the destroyers of whole plants. The destroyers of small areas. Among the simplest of the algal fungi one finds certain kinds which possess a very small m'ycelium so that they occupy only a single cell of the host. This cell the parasite may immediately destroy without effect- ing any change in the surrounding cells. In some cases, how- ever, it may affect neighboring cells and these may grow ab- normally large. Such growth results in the formation of galls. Galls vary in size from that of a pin head, or even smaller, to walnut size, and some galls are known to be even very much larger. Not all plant galls are of a fungus nature; for by far the great majority are caused by the sting of insects when the latter deposit their eggs in the plant tissues. Such are the very common galls formed so abundantly on leaves or branches of oaks, as in the nut galls of commerce. Most small-area-destroying fungi do not confine their at- tacks to one cell but pre'y on a large group of cells. Typical examples of these fungi are found among the leaf spots. These fungi are exceedingly abundant parasites and are usually characterized by the destruction of limited, often circular, spots of the leaf which they inhabit. These spots usually turn brown and are sometimes fringed with a red or white band. The spots of strawberry leaves which are so destructive to certain varieties in our state are excellent examples of leaf spots. Many fungi of this class are very injurious if they occur in abundance, while others do not perceptibly affect the general Minnesota Plant Diseases. 79 health of the host. Certain smuts and powdery mildews may also be confined to small and limited areas. In the former case the area is converted into a smut heap while in the latter it be- comes mildewed and later dotted with the very small spore cases. Most smuts and mildews, ho\vever, are not restricted to small areas. The mildews are seldom confined to small areas FIG. 35. — Strawberry leaf-spot. The fungus (Sphaerella fragariae) destroys small areas of the leaf. Original. of the leaf surface or even to the leaf itself, though usually this is its favorite habitation. The smuts, although often occupy- ing a sharply delimited area, more often occupy whole plant organs, as fruits or stamens. Moreover, the smut mycelium always dwells inside of the leaf while the mildew is external in its habits, except in its sucker-threads. Rusts, though often confined to certain organs of the host, are not usually restricted to particular or limited areas. Methods of killing tissues. There seems to be two ways by which tissues of the host plant are killed. The nutrient sub- stance of the host tissues can be directly absorbed through the membranes of the fungus thread wall and also, in some cases, through the wall of the host cell. The substances are with- 8o Minnesota Plant Diseases. drawn before the death of the host-plant part. In the second case the fungus produces on the surface of its invading threads a chemical substance which kills the host plant tissues and the fungus absorbs its nourishment later from this killed area. It is only fungi which know the first method: that can stimulate their host to extraordinary growth and over production of food material, as in the witches'-brooms. The second method is common among half saprophytes. The destroyers of organs. Many leaf mildews attack so vigorously that the whole leaf is unfit to perform its natural function. In this case the leaf is impoverished and usually turns yellow or brown and falls. In other cases the fungus, while not withdrawing much nourishment, may cause leaves to fall prematurely. Such are often known as leaf-casting dis- eases. The blight of potatoes may extend over all of the foli- age leaves, blighting them and causing death. The death or fall of leaves before the normal period of fall is a serious injury to the host, as every leaf lost is a fractional loss in the manufac- ture of starchy material. The destructive attacks of smuts on the fruit of grasses and upon the stamen of pinks have already been mentioned. Rusts of grasses never, of course, cause the fall of leaves but they may very seriously affect the starch- making power of the plant, and so very materially injure the crop. Branches are sometimes killed off by fungus parasites. Such may be the wound parasites which attack the trunks and branches of trees. The tax which a witches'-broom levies on a branch may kill off, by indirect action, the branch beyond its insertion. Whatever the attacked organs may be, if invaded in sufficient numbers their loss may cause the death of the whole plant. The destroyers of whole plants. There are many fungi whose usual effect of parasitism is the death of the whole host plant. Conspicuous among these is the damping-off fungus which attacks seedlings. Wound-parasites of trees, when they have successfully invaded the trunk of the tree, or root-wound parasite may cause the death of the whole tree. Powdery mil- dews, rusts, and especially the downy mildews, such as the po- tato blight, very often kill the whole plants. Death is here the accumulative effect of the attack on the various organs. Sev- Minnesota Plant Diseases. 81 eral fungi suffocate plants, causing death with or with- out true parasitism. A shelf fungus not uncommon in Min- nesota grows on the ground and often envelopes the bases of shrubs or sap- lings with its dark b r o w n fruiting body. When it meets seedlings this envelopment may prevent the further growth of the host and suffocation re- sults. One of the black fungi attacks several kinds of grass plants and prevents the unfold- ing of the leaves and finally causes the death of its host plant. Stunting of plants and plant parts. Fungus par- asites in many cases do not produce death but succeed only in stunting the host plant or its FIG. 36. — Larch tree killed by the parchment pore-fungus (Polystictus pergamenus). The entire tree was killed by this half-parasite. Orig- inal. 82 Minnesota Plant Diseases. parts. This stunting is shown in a few cases in the leaves of plants. It may be accompanied by a stimulation of certain parts of the leaf. For instance, a very simple little fungus may attack dandelion leaves and produce tiny galls which appear as rough- nesses on the surface of the leaf, while the leaf as a whole is con- siderably smaller than an unattacked one. More frequently one meets with the stunting or total sup- pression of flowers. Some plants, for instance, which may sup- port a parasitic fungus for many years, never produce flowers. Again, curiously deformed flowers are produced in which one or the other kind of floral leaves are missing. Sometimes the floral parts are present but strangely unlike the normal struc- ture ; petals may be green and like simple foliage leaves or like sepals. Fruits may be stunted in their growth. In cherries or plums when the fruit is attacked by certain sac fungi "pockets" are produced. These fruits, though much enlarged over the normal fruits, never produce natural seeds and the stone is also undeveloped. Not only may stunting affect the form and size of the host, but the life of parts may be shortened. The witches'-broom often furnishes examples of such age shorten- ing. Here the leaves may fall long before the normal time. Stimulation of host. More conspicuous and more common is the occurrence of stimulation of the host by the fungus para- site. This stimulation may result in one or more of four effects, viz. : (a) an increase in size ; (b) an age stimulation ; (c) the de- velopment of normally undeveloped organs ; and (d) the forma- tion of new organs. (a) Many cases of increase in size of organs are met with as a result of. fungus parasitism. The fungus galls mentioned above are the simplest cases of such enlargements. The branches of witches'-brooms are usually enlarged not only in size but in numbers. The plum and cherry "pockets" are like- wise enlargements. On the leaves of Labrador tea and other heath plants may be formed large solid galls which are covered with the spores of the parasite. Rusts produce enlargements of the stems of various pines, forming huge spherical, burl-like swellings. Roots of the rushes are enlarged by the attack of a smut fungus. Moreover, floral parts are often enlarged. Petals, sepals, stamens or pistils may be stimulated by fungus parasites to extraordinary growth. Minnesota Plant Diseases. (b) Many rusts have remarkable powers of stimulation, not only in their influence on size but also in the age of parts. Al- though a host plant may bear the load of such a parasite the fungus may still stimulate it sufficiently to enable it to maintain its normal age relationships so that the fungus and host may live together for years. In the darnel grass lives a smut-like fungus which is parasitic and which infects the embryo in the seed before the latter is ripe, and thus this fungus lives on from to vear ASL vear in- fecting its host without the need of spores. Such a partnership has become almost, if not altogether, an equal partnership, and approaches the degree of uni- fication attained among the lichens. (c) Among the most remark- able effects of stimulation are the changes in , i n i , c t"C HOrai partS Ol 1n/^0f ^lit-ifo Tf io l pia«lS. 11 IS well known that in some plants there are two kinds of flowers, one bearing stamens and the other pistils. This is the case in certain mem- bers of the pink family. In these plants, however, this so-called (and incorrectly) "unisexual" condition has been brought about by the failure of the beginnings of one of the floral parts to develope. Thus, we find in such flowers either the stamens alone fully developed, with the undeveloped beginnings of the pistil, or vice versa. Very often such flowers are attacked by certain smut fungi and the parasite often exerts a stimulating effect upon the undeveloped beginnings of the floral parts and 84 Minnesota Plant Diseases. excites them to growth, so that where normally only one kind of floral leaf is developed, two may be produced in the diseased flower. The stamens may be produced in pistillate flowers or pistils produced in staminate flowers. In still an- other case stamens may by the influence of a fungus parasite be transformed into petal-like bodies, thus producing a doub- ling of petals. (d) All of the effects of parasitism mentioned thus far have been either changes in normally developed organs or the growth of undeveloped beginnings of parts. There are known at present only a very few cases where a fungus excites the formation of absolutely new organs. In these cases the organs are produced by the host only when the fungus is present and they have to do solely with aiding the parasite in the produc- tion and dissemination of its spores. Such new organs are known on a cone-bearing tree of Japan closely related to our own white cedar and the fungus causing the formation of new organs is a rust. Effects of parasitic fungi on tissues and structure of hosts. It has already been said that fungi may cause increase in size of plant parts. This increase in size is effected in two ways : first, by an abnormal multiplication of the cells of the tissues affected which takes place under stimulus from the fungus, and second, by the enlargement of each cell. Both processes may go on at the same time. Fungi act differently in their invasion of tissues and each has its own method of attack. This is noticeable in the effect upon the leaf-green of plants. Some fungi cause a decrease in the amount of leaf-green found in the host plant, often effecting its complete disappearance. Such plant-parts have a yellowish color. Certain rusts have such an effect upon their hosts. One may find other cases where only a partial decrease of leaf- green occurs as in the balsam-fir needles on the witches'-broom, also produced by a rust fungus. On the other hand the fungus may excite the tissues to the production of an extraordinary amount of leaf-green, or to the retention of leaf-green after sur- rounding parts have lost it. Such green spots on leaves have been known as green islands and are striking examples of the unification of fungus and host-parts into a virtual individual. Minnesota Plant Diseases. 85 Fungi are even known to excite the formation of leaf-green in plant parts usually devoid of it, e. g., in petals of flowers, as is the case in the white rust on mustard plants. In this case it is very probable that we see simply the stimulation to the devel- opment of latent beginnings of the leaf-green bodies, just as the stamens and pistils are sometimes formed in flowers usually de- void of them. As leaf-green furnishes the machinery for starch- making, one sees that the amount of starch formed in a fungus- inhabited part may vary with the fungus. However, leaf-green is not the only agency of starch production. There are other agencies for the transformation of starch from other com- pounds. Aside from the effect of the fungus upon leaf-green, fungi react directly upon the starch, producing certain chemical substances which dissolve the starch. Some fungi use all of the available starch as soon as it can be reached, while others cause a great accumulation of starch temporarily and dissolve it in the important stages of their life history, during and just preceding the formation of spores. A great many fungi are able to dissolve starch and among them may be mentioned cer- tain rusts, black fungi, white rusts and many wood-destroying fungi. \\ hen tissues of plants are examined under the microscope a honeycomb-like structure of cells is seen. The walls of most cells are whitish, soft and composed of a substance called cellu- lose. The walls of the cells of woody tissue enclose in the youngest stages the protoplasm, but soon lose the latter. The "woody" character of wood tissues is imparted by the thickness, size and form of their cell walls, and the chemical compounds found in them. In young stages, the wall is whitish and not particularly resistant nor hard, for it is a cellulose wall. Later new substances are added, which collectively are known as lig- nin, and the tissues then become woody. But woods differ among themselves due to variation in the above-mentioned characters. The cellulose membranes are sometimes pierced by fungus threads in a mere mechanical fashion, just as one would force a pin or needle through them. Wood membranes offer considerable resistance to most fungi, but some of the latter have solved the problem of penetration of these walls. Such are the wood-destroying fungi already mentioned. The 86 Minnesota Plant Diseases. threads of these parasites exude certain chemicals which are able to attack the lignin of woody tissues and to dissolve out the substances which make up this lignin. These cell walls now have the same chemical constitution which they had before they became lignified. But the fungus is also able to attack the cellulose walls and the final result is a more or less complete breakdown of the walls. The wood crumbles easily and is con- verted into punk, which is characteristic of rotten wood. The threads make their way from cell to cell, usually by boring through the walls, whether they are wood walls or cellulose walls, and in tissues attacked by these fungi one sees large numbers of holes through the cell walls, where fungus threads oooo FIG. 38. — Two ways in which wood is destroyed by wood-rot fungi. On the right the wood cells are destroyed from within outwards. On the left they are destroyed from the middle of the wall toward the center of the cell. Highly magnified. After Hartig. have passed. From these points the dissolving substance spreads over the cell wall completing the rotting process in that vicinity. Since woody tissues can be colored characteris- tically by using certain chemicals, one can determine by the use of these chemicals just how far the rotting has proceeded. It is worthy of notice that fungi have different methods of attacking and rotting woods, using different substances and ap- plying them in various ways. The study of the rotting of woods is still in its infancy, but it is now known that certain wood rotting fungi can be determined by the kind of rot which they produce. The wood-rot, therefore, often gives very def- inite symptoms of determinable diseases. The study of wood- rots is receiving considerable attention at the present time on Minnesota Plant Diseases. 87 account of its vast importance economically. To realize this importance one has but to think of the great losses sustained yearly by the decay of mine timbers, house-foundation and cellar timbers, of bridge-timbers, railroad ties, paving blocks, fence posts and rails — in fact, timbers wherever air and moisture can reach them. The creosoting of pavement blocks and the tarring of cedar posts are attempts to aid the wood in resisting fungus attacks. Tar and creosote are substances in which the fungi cannot live and their presence protects the wood. But as soon as the substances are washed off the fungi commence their attack. At present a considerable amount of money is being expended to find a process or substance which will pro- tect railroad ties from fungus rot. What is wanted is some substance which when deposited in the wood will prevent the entrance of fungi and which will not readily leach out into the soil during heavy rains. Effects of parasites on anatomy of host. The effects of fun- gus parasitism described above have to do with the destructive attacks upon cells and tissues, particularly in those cases where enlargement of parts is caused. One often finds other effects in tissues, viz. : changes in quality and amount of certain kinds of tissues. The covering layer is often affected by fungi which live on the surface, and may also be ruptured by the spore-pro- ducing hyphae of interior-dwelling fungi as in red rusts. Some fungi excite in certain plants an abnormal growth of cork which constitutes the cuter layers of the bark. In general, in the en- larged parts of the hosts, the supporting or strengthening tis- sues are not as well developed as in the normal host. Many tis- sues, moreover, which are usually woody are not so in the dis- eased and enlarged parts, although there are exceptions to this generality. Sometimes the fungus attack stimulates the ex- cessive production of resin in pines and their allies. Other products and tissues may undergo change, though no generali- ties can be discovered in the action of fungi. It seems, how- ever, that, in general, those changes take place which transform the host part into a most suitable and profitable dwelling and food store for the parasitic fungus without regard to the host's needs, and often to the direct detriment of the host plant. There is usually in this connection a great amount of tissue 88 Minnesota Plant Diseases. produced which is especially fitted for storage of food materials. The cells therefore are large, thin-walled, closely crowded and contain much starch and other storage food. Effects of hosts on parasites. In the unequal partnership of host and parasite, where the fungus is the dominant partner, the latter is often profoundly affected by the host plant. It be- comes so accustomed to peculiarities in the life history of cer- tain plants or groups of plants that it has learned to shape its own course in harmony with these peculiarities. First of all, then, one finds a parasite capable of living on but one particular kind of host — it is found on no other, and an attempt to* culti- vate it on even the most closely-related plants fails. Such a condition of parasitism, though by no means unknown, is not very frequent. Far more common is that condition where the parasite has learned to shape its general habits to comply with the peculiarities of each of a group of plants very closely re- lated and is capable of infecting any of them. It is found, how- ever, that the previous habitation of a fungus has in some rusts at least an important effect upon the spore of that rust in the infection of other host plants. In general, infection succeeds best upon the identical kind of host upon which the spores were formed, while the nearest relatives of this host are more easily infected than are distant relatives. One must infer from these facts that the effect of nutrition, etc., received during habitation on a host are far reaching and influence the fungus towards a preference for this same host. Certain fungi, again, are able to attack any of a number of host plants which are but widely related. Such fungi show general abilities and no special education in selection of host. In other words, they are not so deeply affected as the previously mentioned specialists. It has already been noted that certain rusts, in order per- haps to produce spores continuously throughout the season, have learned to live on different hosts at different times of the year. Such fungi may also exercise exact preference for their hosts, though, of course, two hosts are necessary. The influ- ence of the host-effect may here be carried over through the life on the second host until the fungus again inhabits the first host plant. Such an impression must indeed be a profound one. Minnesota Plant Diseases. 89 Host-influence on parasite may be exerted even at the time of spore germination. The spores of a great many parasitic fungi will start to grow when placed in pure water. Some fungi, however, as most of the smuts, require nutrient material before they will germinate. Again, other fungi must bring their spores into direct contact with the host plant in order to bring about germination. After the spore has germinated the germ-tube penetrates the tissues of the host plant. In some cases, where the fungus spore is not directly influenced in its germination by the pres- ence of the host, a spore may germinate on an unfavorable host and the germ-tube may even penetrate into the tissues, but here its progress is prevented as the host does not permit of further growth. Such a struggle may continue for some time, but is usually short if the host is at all unlike the usual host of the fungus. The preference shown by fungi for special plant parts as dwelling places, as the grass-fruit-inhabiting smuts, is but another expression of the influence of the host plant parts upon the fungus. Chapter VII. Fungi. Plant Diseases* Jff Disease in plants. It is not always an easy matter to tell whether or not a given plant is healthy or diseased. For in- stance, a plant may be placed under very slightly unfavorable conditions of moisture and sunlight. If it were to obtain slightly more or less moisture or sunlight, as the case might be, it would thrive or sicken. Still the unhealthiness of such a plant would hardly be termed a disease. If, however, we were to further change the unfavorable surroundings, we might bring the plant to a condition where its life would be seriously threat- ened and such a plant would unhesitatingly be called diseased. We can therefore see that one may conceive of all sorts of possible conditions between so-called good health and undoubt- ed disease in plants, and that disease and health are only con- ventional marks, as it were, on an artificial scale of the life con- ditions of organisms. No plant ever enjoys all of the best con- ditions possible for it can only approach such a condition. If it could, it would touch the top mark of the life-scale ; the bot- tom mark is the disease-death of the plant. We might say a premature death instead of a disease-death because it must be remembered that all plants as we know them today are destined to die sooner or later. Some, as many of our common weeds, live only a year, while, on the other hand, our great forest trees live for centuries, but sooner or later their constructive powers are no longer successful in repelling the attacks of unfavorable conditions and they succumb. Such a "natural death" is not in the nature of a disease, as we commonly understand that term. Yet disease merely hastens this death, and again we might trace all conceivable conditions between an imperceptible has- tening of death to a violent death from a well-defined disease. All of the efforts of agriculturists and horticulturists are summed up in saying that the conditions of growth of selected Minnesota Plant Diseases. 91 plants are artificially favored. The fertilizing of soils, the selec- tion of various soils for certain plants, processes of cultivation, and so on, are all directed toward this end. Men engaged in these pursuits are fast learning to recognize the advantages and profits of such processes and no improvement, however small it may be, is too insignificant for notice and application. We might term such processes improvements of health. There is another aspect which often escapes the busy prac- tical farmer or horticulturist of today. In the absence of an analysis he recognizes in disease only those sharply marked or violent disturbances which are very obviously threatening the life of his plants. The small losses by inconspicuous diseases are often overlooked. For instance, no farmer fails to calculate his loss when a heavy rust epidemic attacks his wheat or an epidemic of smut invades his oats. Few farmers, however, realize that every year rust levies a tax of a fraction of his crop, although that fraction may be small. Why should he not be alive to these facts and to the necessity for alleviating such troubles as he is to the small improvements of cultivation and introduction? And such conditions can only be improved by a fair intelligence of the cause and spread of the diseases of plants. It is only by such knowledge that intelligent remedies are applicable and the greatest profits attainable from the products of the soil. It is only then that our plant proteges will at all approach the highest mark of good health. It is a well known fact that the offspring of a plant may vary considerably in their characters. If we take an extreme case we can easily imagine two offspring of one plant to be so dif- ferent in character that under the same conditions one would thrive very well while the other would suffer very perceptibly. The variation in the latter case would be indistinguishable from disease for it tends under existing conditions to prematurely end the life of that plant. Of course such a plant, if placed un- der different conditions, might thrive exceptionally well, and man's great interest in variation is the puzzle of fitting together varieties and conditions to the best advantage. As seen in one light the life of a plant is unlimited in time — is, so far as we know, immortal through the germ cells which contribute to the formation of new offspring. Individuals, 92 Minnesota Plant Diseases, however, have a limited life. A plant evinces two processes constantly at work, viz. : a constructive process which is build- ing up the tissues, increasing or replacing them, and a repel- lant process which organizes and otherwise provides for the repulse of unfavorable conditions among which may be includ- ed the attacks of injurious weather and soil conditions as well as those of fungi and other organisms. Now in the normal vigor of youth a plant is capable not only of successfully re- pelling external attacks but puts much energy into the con- structive work. Gradually less and less of an increase of tis- sues is noticeable because of the necessary replacement of lost tissues and finally we reach the mature vegetative condition of a plant where the latter has attained its greatest possible size and all of its constructive power is exerted to replace lost mem- bers or parts. If conditions were ideal, one might imagine such a mature or prime condition to last indefinitely, but now with the increase in size and complexity we find also an increase in the attacks of foreign organisms or the unfavorable conditions due to accidents, as lightning strokes or storm damage. If the repelling power of the plant does not increase, the disintegrat- ing forces gain and the plant enters the period of old age and decline which is terminated only by the complete success of the disintegrating forces, i. e., the death of the plant. Among the shortest-lived individuals are those plants which live but a single season. Among the longest-lived are not only our giant trees but also those herbaceous plants which have creeping underground stems, that travel from year to year, carrying their reserve material as a capital for starting work again in the following spring. Such plants as iris, bloodroot and many of our grasses are good examples of such long-lived plants. The at- tack of some foreign organism has in general more chance of success during the old age period than during the vigor of youth and old age in a plant, therefore in general predisposes that plant towards disease. Factors of disease. Disease in plants has these three fac- tors : first, the immediate cause of disturbance, as a fungus or some insect or some unfavorable atmospheric agency; sec- ond,, the resultant change in the life of the host ; and third, the previous condition of the host plant, i. e., its predisposition in Minnesota Plant Diseases. 93 particular towards that disease. The first factor will be con- sidered later. The second has been discussed in Chapter VI. We will now examine mo-re in detail the third factor, i. e., pecul- iarities in internal and external conditions which make a plant more or less susceptible to disease. Predisposition. This susceptibility is in almost all cases a specific one toward a certain disease and less often toward many diseases. When a plant is subject to the attack of numerous agencies wre can easily imagine some change in conditions, as, for instance, transplanting from a dry to a moist atmos- phere, which would favor the attack of all of these diseases. The conditions become such that fungus attacks in gen- eral are facilitated. But most predispositions are in the nature of special conditions which are favorable to only one spe- cial disease or class of diseases. This distinction is expressed in the terms general and special predisposition. An illus- tration may make this clear. Wheat rusts are of different kinds caused by several fungi. In general, moist warm weather in the growing season predisposes all kinds of wheat plants in many ways to the attack of rusts, and such conditions furnish general predisposition. But if a certain variety of wheat be particularly susceptible to a given rust fungus, abundant in the region into which the wheat is introduced, the new condition of position in the wheat plant predisposes it very much to that disease. Other varieties of wheat, less susceptible to that par- ticular disease, might be unaffected so that we may have here a special predisposition. It is a fact which must not be lost sight of, that the predis- position of the plant in itself may not be harmful to that plant, but may be a condition which might be highly recommended when considered alone. But it is the other factor, the fungus or insect, which may be the disturbing influence and which is especially favored by this condition of the host plant. Such a distinction is of very great importance to practical agricultur- ists and horticulturists because it is not only the immediate condition of the plant or, on the other hand, the presence of disease-causing conditions, but it is the relationship between these two factors that is all important. There is another fact of great importance that must be emphasized. No plant, as far as 94 Minnesota Plant Diseases. is at present known, ever inherits a disease — no disease passes directly from parent to the offspring plant in the germ cells. Predispositional characters may be inherited but the first dis- ease factor is never inherited. The infection of the host plant may take place so early in life that at first sight there may ap- pear to be an inheritance, but all such cases at present known have been shown to be simply early infections of the host plant. For instance, oat plants are infected in the seedling stage just after the little plant arises from the grain, while in the darnel grass the infection of the host plant takes place inside of the seedling before the seed is ripe — for, as is well known, the little plant is already well developed when the seed is ripe and has been growing for some time previously. That is to say, in the darnel, the plantlet (commonly called the "germ") inside of the grain is already infected with the fungus. But in neither of these cases is there an inheritance of the disease. Kinds of predisposition. Predisposition may be therefore of two kinds, the natural and inherited condition of structure and habit due to internal causes, and the accidental or abnormal conditions which are due, not to internal inherited traits, but to the accident of external forces. Thick-skinned potatoes are known to be more resistant towards certain rots than thin- skinned potatoes, i. e., the thin-skinned forms are naturally predisposed in their structure to that disease. Again, oat grains germinate at about the same time when the oat smut spores germinate and hence the young oat plants are predis- posed to smut attacks by their inherited habit of germinating in the spring. Such might be termed a natural predisposition of habit. On the other hand, a wounded plant is predisposed to- wards the attack of wound parasites by an external force as in pruning, or by wounds caused by cattle or deer, or a wagon wheel, and is more liable to such attacks after receiving a wound. Again, the transplanting of plants from a dry to a moist climate may predispose such plants to disease. Here the pre- disposition is induced by external factors. It is noticeable that in both of these predispositions of external cause the pre- disposition as in a wound or in transplanting may not in itself bring about serious injury to the plant. Plants have an effect- Minnesota Plant Diseases. 95 ive method of healing over wounds and a removal from a dry to a moist atmosphere frequently stimulates the plant to ex- traordinary growth. But it is in opening a new field of attack for invading organisms and other disease-causing factors that such externally caused conditions may prove dangerous to the host-plant. Many other plants besides oats are predisposed towards dis- ease during their youth or during the youthful stages of certain organs. The corn plant is attacked by the corn smut only in young growing parts and the fungus cannot invade mature tis- sues. Certain conditions of the youth of plants aid in the at- tack of disease; for instance, the thinness of the tissue skins, and the abundance of food material. It must not be assumed that all plants in their infancy are predisposed towards disease, but there are certain conditions which may in general tend to increase susceptibility towards disease. Perhaps the prob- lems of old age are still more productive of predispositions. Young tissues have the advantage of vigorous protoplasm, while aged plants have reached their limit of growth and are losing ground. Again, seasons may bring predispositions, as in the oat smut, for several causes may contribute to the same predisposition. A rest period may also be productive of dis- ease since the protoplasm is not as active in resistance when resting as in the rapidly growing condition. Such is the case of the ripe rot of fruit. Predispositions of form have already been cited in the thin-skinned potato. Immunity from certain diseases sometimes comes with wax-coated surfaces or thick cork, etc. Physiological habits of plants, as in the oat smut, are likewise productive of predisposition or immunity. Such habits as in the germinating period of grains growing in differ- ent regions may be important in assisting the plant to escape disease. This is the partial explanation of the advantage of selection of seeds growing in certain regions, e. g., northern grown seeds for northern localities. Plants kept under peculiar conditions of moisture or tem- perature may acquire a predisposition towards disease. Hot- house plants suddenly planted in very dry conditions are some- times not able to adjust their water evaporating apparatus to the dryer conditions and suffer wilting and accordingly in some 96 Minnesota Plant Diseases. cases death. Likewise, when trees grown in the protection of forest shade are suddenly transplanted to a prairie or isolated by the cutting down of surrounding trees, they may fall a prey to sun scorch. External causes may be fertile in many other predisposi- tions : Wounds by pruning, root injuries, insect boring, hail- stone wounds and injuries by lightning strokes, frost cracks and sun scalds, etc. It has already been explained that disease is never inher- ited. On the other hand, it is a fact that natural conditions, e. g., of form or of habit, which are, in reference to certain dis- eases, causes of predisposition or immunity, may be inherited. Such accidental conditions as wounds are of course not capable of transmission. In other words, only natural or so-called normal predispositions are inheritable. Variation and predisposition. The selection of varieties in agriculture and horticulture is very greatly concerned with this phase of the subject. Variation in structure, form and habit give to plants different degrees of resistance toward certain dis- eases, some greater and some less. Of course there is likewise variation in respect of other conditions and one may select vari- eties for those conditions. For instance, wheat varieties may be selected for their fitness for milling, size of grains, crop yield and other characters. Fruit tree varieties are selected for size of fruit, keeping qualities, yield and so on. Now one can also select varieties of agricultural plants for the resistance which they exhibit towards a given disease. For instance, cer- tain varieties of strawberries will resist the strawberry spot fun- gus more successfully than others, and where this disease is prevalent might be very desirable. Again, some apples or crabs are more susceptible to apple scab than others, and the selec- tion of these varieties may be a distinct advantage. Of course such varieties might not be the most desirable in other respects. In other words, the intelligent grower of plants has before him a very complex problem. The object to be gained is the best crop under the existing conditions. These conditions he must know thoroughly before he can solve the problem, and the varieties must be selected accordingly. It should be empha- sized that the conditions must be thoroughly understood and Minnesota Plant Diseases. 97 the difficulties appreciated. If they are not, the plant grower is working in the dark. The wheat rusts furnish a good illustra- tion of the complexity of the problem which is presented. Wheat rust may be caused by one or more of several kinds of fungi which are very closely related but are nevertheless dis- tinct kinds. A wheat variety which might resist one of these would be unable to resist others. Now an intelligent solution of the problem must include a knowledge of the particular rust fungus attacking wheat in certain localities and then varieties must be selected which will resist this particular fungus. If more than one fungus is prevalent in this locality the selection of a rust-proof variety becomes more difficult. In other words, rust-proof varieties may have to be selected for certain kinds of rusts and not for rusts in general, although, on the other hand, it is not conceivable that certain varieties may possibly be de- veloped which will offer general resistances to the whole group of rusts, e. g., where they are able to withstand the predisposing effects of moisture, or in their early or late sprouting habits might dodge, as it were, the time of year when rusts' spores are most abundant. Early sowing of wheats was an attempt to evade this period of the year but not as yet with very conspicu- ous results. In a word, the greatest success in selection of vari- eties is still to be obtained, but can only be won by more knowl- edge of the habits and forms both of the hosts and of the fungus causing the disease. More knowledge and the hearty coopera- tion of the practical plant grower with the plant disease special- ist are the requirements of the solution of these complex prob- lems. Infection of host. We have already seen that fungi use vari- ous methods and agencies for the distribution of spores and there are consequently various methods of inoculation of host plants. In the first place it must be pointed out that inocula- tion and infection are two different things, e. g., a plant may be inoculated with fungus spores which may even start to grow, but a successful continuance of growth does not always follow. When the fungus does succeed in living with the host, infection in the true sense is accomplished. Infection is successful inocu- lation. 98 Minnesota Plant Diseases. The wind transports many fungus spores from plant to plant and some great plant epidemics are due in part to this agency. It seems possible that red rust spores may be blown from warm- er climates, where they pass the winter, many miles, inocu- lating in the early summer or spring the plants of northern countries where the summer spores cannot be formed through- out the year. Inoculation of some fungi occurs chiefly through swimming spores and in such, only wet seasons will enable the disease to become serious. Such a parasite as potato blight will spread with remarkable rapidity on plants in low, damp situa- tions or during excessively moist weather. Some of the algal fungi, as white rust, combine the two methods in distributing by means of the wind, spores which in subsequent rainy weather break up into swimming spores and thus act as new centers of inoculation. Insects carry spores of fungi from plant to plant and are allured by "honey dew" or by other sweet and odorous liquids. In the case of ergot of rye the insects are attracted by a honey-like fluid, which is exuded by the young grain, on which the fungus has formed an abundance of summer spores. These are then carried by the fly to other young flowers and the disease thus spreads rapidly. It is known that many other ani- mals effect the spread of plants by distributing spores under favorable conditions. The furry coats of some rodents have already been mentioned as depositories for spores. Man is re- sponsible for many inoculations of fungus spores on plants. All of the numerous methods of transportation and travel and commercial intercourse furnish means by which man scatters spores of fungi, often bringing them into most favorable condi- tions. The introduction of mallow rust from South America has already been cited. Careless pruning or wounding of trees, untidiness in horticultural and agricultural pursuits and lack of knowledge of the nature and various methods of infection of certain diseases all conspire to make man an efficient aid in the spread of fungus plant diseases. In manure heaps dangerous fungi often multiply or pass the winter. The debris of trees or other plants which have been diseased is also a menace. The various farm implements, in passing from one place to another, may carry spores and effectually scatter them. The sowing of smut-infected oats without taking the precaution to kill off the Minnesota Plant Diseases. 99 fungus is a good case in point. Finally, the fungi may actually aid by special devices the spread of disease. Such devices are seen in the sac fungi where spores are forcibly ejected and so, caught by the wind, are easily scattered. Again, infection may take place not only by spores but also by mycelium, and does so in many cases. This is noticeably true in those fungi which FIG. 39. — A good example of an epidemic. Potato blight has, within a week, entirely destroyed the potato plants in this field. After Clinton. attack trees and particularly root parasites. Contact between a diseased tree trunk or roots and a healthy one may offer the mycelium a chance to pass over directly from the one to the other and a successful, infection may ensue. Some of these fungi have a special shoe-string-like strand of threads which are especially proficient in effecting mycelial infection. ioo Minnesota Plant Diseases. Epidemics. When a fungus disease becomes particularly abundant and devastates great fields or forests of certain host plants there arises an epidemic. There have been notable epi- demics of continental extent in historical times just as there have been famous plagues attacking man. Potatoes have many times been decimated by the blight, forests have been threat- ened by the honey mushroom ; the mallow rust has swept over Europe and America damaging many kinds of mallow; while year after year one may read of epidemics of grain rusts and of smuts. These epidemics are more widespread in some years than in others. This last season (1904) has seen wheat-rust epidemic almost throughout the northwestern United States and Canada. In Ceylon the coffee disease has ruined hundreds of coffee plantations. A remarkable fact in these epidemics is that the fungi which produce them may have been present a long time previous to the epidemic without exciting any great amount of damage. It is well known, for instance, that potato blight, wheat rusts, mildews and smuts are always with us, but that not every year furnishes epidemics. It is therefore evident that other factors besides the immediate cause or fungus fac- tors must be present. Of these, weather conditions are usually the most important factor. Potato blight never thrives in dry weather or on plants in sandy soil, but is at its best when the weather for days is misty and moist so that the fungus can form its swimming spores and distribute them rapidly. It is just in such weather as this, and particularly after a warm growing sea- son, when the leaves are swollen with moisture and rich in food material, that blight strikes. Several of such epidemics of enor- mous extent have been known. It is also a well-known fact that wheat rust often follows upon very moist springs and early summers. In fact many people still think that the wet weather causes rust. And they are not altogether wrong, but the effect of the weather is not exactly as such people imagine. Warm, moist weather is just the kind of weather which is favorable to the development of the summer spores of the rust fungus and the fungus grows luxuriantly, producing in two weeks or less another crop of summer spores, thus multiplying an hundred or a thousand-fold in this short time. Minnesota Plant Diseases. 101 i > g^ S "*. Cfl &5 •c^ *o S- ifs P' |S IO2 Minnesota Plant Diseases. The success of smut infection depends largely upon the abil- ity of fhe spores tc germinate and the germination of the spores at a suitable season for attacking the host-plant, e. g., in oats, in the seedling stage. An epidemic of smut must, therefore, be preceded by a season favorable to spore germination and also coinciding with the seedling stage of the grain. Such epidemics, moreover, are greatly favored by the clinging of smut spores to the grains since they are thus sure to be near the latter when these commence to grow. Many other causes of epidemics might be mentioned. Un- der so-called normal conditions the fungus may create no ex- traordinary damage but under propitious conditions it becomes epidemic. One can easily understand that any disease may be- come epidemic if the conditions are right, and since the horti- cultural and agricultural changes instituted by man are so great in many cases it is to be expected that the danger of epidemic diseases is always an important and ever-present source of trouble. The older horticulturists and agriculturists took cog- nizance of epidemics only after they occurred, when, of course, remedial measures were impossible. Now the raiser of plants, just as does the medical practitioner among men, keeps close watch upon all kinds of diseases and attempts to prevent epidem- ics rather than to cure them. Every introduction of a plant into a new country and new surroundings, every appearance of a new hybrid opens up new fields for numerous parasites who may find in the newcomer just the right conditions for an epidemical growth. Every introduction of a new plant to a certain com- munity may also bring new fungus diseases which may be able to attack plants of this community if the latter have not learned to withstand their attacks. Thus may result an epidemic simi- lar to that of mallow rust. It is useless to suppose that we shall ever get rid of the plant disease question and be able to lay it aside under the weight of a few rules for spraying or other treatment. On the contrary, the more complex and ad- vanced our agriculture and horticulture become even more so becomes the question of immunity from fungus epidemics. As the host plants vary so also may the fungi, and those parasites which are apparently harmless today may in years to come be very dangerous pests. Chapter VIII. Fungi* Kinds of Fungi* Algal Fungi* Jff The fungi are undoubtedly descended from algal stock and, as commonly understood, more than one line of descent is prob- able. That is to say, the ancestors of the present day fungi were all algae, though of at least several kinds. The algae com- prise a group of plants which have in general a water-habit. A great many fungi still retain this water-habit but unlike the algae, which possess leaf-green, they are unable to manufacture their own food. On the other hand, a vast number of fungi have learned to live in the open air or in the tissues of other plants or on the ground ; in short, have abandoned the aquatic for some terrestrial habit. With this change in habit have gone on changes in form and methods of reproduction. Botanists recognize three great groups of fungi. The lowest group is that of the algal fungi, including those of which the majority have retained the aquatic habit and in which the reproductive methods have been less strongly altered than in the two remain- ing higher groups. The latter groups are in general terrestrial, and have adopted two very distinct methods of reproduction. In all of the sac fungi spores are formed inside of sacs and these sacs in most forms are elongated cylinders containing eight spores each. In the stalked fungi the spores are produced ex- ternally on fungus threads, and are borne on fine and delicate stalk threads. The number of such stalked spores on each thread is commonly definite for any given species and the usual number is four. The production of spores by breeding is known to occur throughout the algal fungi and has been ob- served in many cases among the sac fungi and probably occurs throughout the latter group. Up to within recent times no undisputed evidence had been produced of the presence of a breeding act among the stalked fungi ; but it is now known that iO4 Minnesota Plant Diseases. a fusion process takes place and this has been interpreted as a breeding act by some botanists. The algal fungi (Phycomycetes). It has already been stated , that these fungi are for the most part aquatic in habit but that some forms, as the insect molds and black molds, have aban- doned the water and taken to dryer situations. It is a noticea- ble fact, however, that even insect molds and black molds re- quire very moist conditions. It is in the algal fungi, therefore, that swimming spores are commonly produced and especially, though not exclusively, in the aquatic forms. White rust of mustard produces swimming spores at certain stages, but this only occurs when an abundance of water is present, so that the fungus may be considered aquatic during a part of its life and terrestrial during the remainder. Spores are produced by a breeding act and often these are special spores for resting pur- poses; they are therefore provided with very thick walls. In some families, as in the black molds, large numbers of spores are produced in cases which to the naked eye look like tiny black spheres about the size of a pin-point. These spores are not provided with swimming lashes but depend upon the wind for aerial distribution. The algal fungi are structurally pecul- iar in that the threads have no crosswalls except when spores or spore-cases are about to be formed. The following groups are the most important among the algal fungi : Chytridines or Lowly Algal Fungi, Water Molds, Fish Molds, Sewer and Drainpipe Molds, Damping-off Fungi, Downy Mildews, White Rusts, Black Molds and Black Mold Parasites. Lowly algal fungi (Chytridinece). In this group are found, in general, very simple fungi. All of them are minute and it requires strong powers of the microscope for the observation of most of them. The simplest are tiny single-celled spheres and resemble much the Flower Pot Algae, except that they have no leaf-green. In fact, it is very probable that they have descended from these algae. Some have become elongated into simple threads and still others are even considerably branched. Spore cases and breeding spores are produced and each forms, by internal division, swimming spores. These swimming spores are the chief agents of distribution and are provided with one or two lashes which, by whipping about in Minnesota Plant Diseases. 105 the water, drive the spore forward with a combination of a hop- ping, whirling and swimming motion. These spores, when they come to rest, draw in their whips and immediately grow out into the mature plant. The function of the resting spores, whether a breed-spore or not, is to tide the plant over unfavora- ble seasons. When breeding occurs, the two breeding organs are exactly alike and indistinguishable, as is the case in some pond scum algae. These lowly fungi are found in a great variety of habitats. Most of them are parasitic, though some are saprophytes. They are found on algae as well as on lowly water animals or on the eggs of the latter. Some are found on fungi, par- ticularly on water and fish molds, while a large number inhabit the leaves and stems of the flowering plants. In their parasitic habitat they often arouse the host to extraordi- nary growth and swellings or galls are thus produced. Hence they are some- times known as gall fungi. Galls of this nature are produced on the leaves of dandelion, anemone and on garden plants such as cabbage. Few, how- ever, produce diseases of very great importance. In that they damage algae and water animals in the waters of fish hatcheries they injure or diminish the food supply of the young fish. One spe- cies attacks and gains entrance to pollen grains of the pine when the latter lie on the surface of water or are submerged in ponds, and lives inside of the spore until it forms its swimming spores when the latter are thrown out into the water. Some have even learned to penetrate and to live in the pill-box algae, which are provided with walls of silica. (Figs. 41, 211.) Water molds and fish mo\ds(Saprolcgniinece in part). These fungi are more highly organized than the group of fungi just discussed. In the first place they all possess a branched and well developed system of thread mycelium. They are, how- FIG. 41. — A lowly algal fungus. Above, the resting condition of a single-celled fungus in the tissues of the host plant. Below, young fungus plants are seen in the cells of the host. Highly magnified. After Schroeter. io6 Minnesota Plant Diseases. ever, all aquatic in habit and thrive in stagnant pools where decaying animal and plant materials are particularly abundant. They are typically half-saprophytes, passing most of their life feeding on dead material in the water, but living parasitically on fish or other animals, as occasion presents itself. As wa- ter plants they utilize the swimming spores and these are usual- ly formed in enormous numbers in spore cases of various shapes. The swimming spores are of the same general struc- ture as those of the lower algal fungi, though in a few cases they seem to be unable to get out of their spore cases and they then grow out into threads while still inside °f the case and never develop whips. All the fish and water molds develop breeding organs of two kinds, male and female. The female organs are usually spher- ical cases, which contain a small number of eggs, and the male organ is an elongated thread which is sometimes branched and usually arises from the same thread which pro- duces the swollen egg case. Now the male thread pene- trates the egg case and can be seen making its way between and around the eggs, but a remarkable feature lies in the fact that they never as far as has yet been observed breed with the egg cells. The latter nevertheless FIG. 42.— Water and fish molds. 1. A fungus thread with an unopened spore-case. 2. An opened spore-case with the escaping swimming spores. 3. An egg-case with the male threads penetrating it. The spherical bodies in the egg- case become the resting egg-spores. Highly magnified. 1 and 2, after Thuret; 3, after DeBary. Minnesota Plant Diseases. 107 seem to be stimulated for they now become the egg spores whose special function is that of resting spores. They cannot be made to develop further until they have rested for some time. After this rest period they divide up internally into swimming spores. These water molds grow luxuriantly on almost any kind of decaying organic matter in the water. When the bodies of dead insects, such as flies or grasshoppers, fall into the water they soon become surrounded by a halo of fungus threads from the water mold which quickly forms swimming-spore cases in countless numbers. When the nutrient material becomes scarce egg spores are produced. Dead minnows or fish are also quickly attacked by these fungi and the rapidity with which the fungus spreads is well seen in the growths on a fisherman's minnow bait. Not only are dead fish attacked. When living fish have suffered the loss of a few scales or some other slight injury, the fish mold may gain entrance through this spot and may spread rapidly as a parasite and finally kill the fish. It may even gain entrance through the gills or in the eyes of the fishes, and it very frequently attacks their eggs. The fish molds therefore may become dangerous pests in hatcheries. Numerous epidemics of these molds are known to have de- stroyed myriads of fishes in their native streams and lakes as well as in hatcheries. Not only fishes but other aquatic animals such as mud puppies and probably other amphibians are sub- ject to attack, as are also many of the tiny microscopic water animals so abundant in stagnant pools and lakes, and thus the fungus preys on the food of fishes. A few forms are known which attack the pond scums. As is to be expected in such plants, the parasite is not of a high type, i. e., no exact selection of host seems probable though this simple method is highly proficient in its own way. The proficiency is due largely, no doubt, to the great number of swimming spores formed and the rapidity of their formation. (Figs. 32, 33, 42.) Sewer and drain pipe molds (Saprolegniinea in part). It is to be expected that sewer- and drain-pipes would offer favorable habitats for fungi of the general habits of the water molds and there are fungi which are constantly found in these places. A large amount of decaying organic material is always present to- io8 Minnesota Plant Diseases. gether with constant moisture. These fungi are close relatives- of the water-molds, differing from them in the long-beaded shape of their threads and in the presence of but one egg in the egg-case. Swarm-spores are again the chief means of distribu- tion, though bits of the threads may be carried along in the pipes and become lodged. By growth these again produce an- other colony. In all kinds of drain-pipes,, in sewers or in the drains of refrigerators- these molds abound. They form dense, compact masses of mycelium which may ultimately stop up the pipe and thus cause trouble. They may also abound in streams, below factories or at the mouths of sewers, and may form large woolly masses of mycelium. (Fig. 43.) Damping-off fungi (Saprolegniinecein part). These molds are also relatives of the water-molds but have approached more nearly to the terrestrial habit. In fact many of them are able to live com- fortably in a very moist atmosphere, though typically they live in or at the surface of the water. The damping-off fungi have swimming spores and egg- spores; only one egg is produced in a case and the breeding between egg and male elements has been observed. The egg-spore is again a resting spore. Like the fish- and water-molds the damping- off fungi may live as saprophytes upon dead organic matter in the water. Many of them are, however, parasitic on algae, such as pond scums and green felts, while a few attack pinworms. By far the most common forms are, how- ever, those which cause the disease known as damping-off. When seedlings, particularly of the mustard family, are sown very thick and are kept very moist, the damping-off fungi ap- pear. They attack the seedlings just at the surface of the soil or FIG. 43 — Sewer-pipe fungi. 1. Fungus threads with pecu- liar constrictions. 2. Same (more highly magnified) , with characteristic gran- ules near constrictions. 3. Swimming spores. High- ly magnified. After Pringsheim. Minnesota Plant Diseases. 109 below it, killing the tissues and the seedling tumbles over and is further appropriated by the fungus. In this way the fungus gains strength and large numbers of seedlings may fall. Not only mustards but clover and beet and other plants are subject to at- tack. In the slight preference of host, the damping-off fungus shows a slight indication of advance in parasitic methods, but the latter are still primitive and success only attends such favor- able conditions as excessive moisture and crowded host plants. (Fig- 34-) FIG. 44. — Downy mildews. 1. Downy mildew of seedlings (Phytophthora omnivora) ; formation of egg-spores by breeding act; a male cell and egg-cell case. 2. Potato blight (Phytophthora infestans), thread with spore-like swimming-spore-cases (s). 3. (Peronospora alsinearum.) Formation of egg-spore by breeding act in another mil- dew; letters as in 1. 4. Egg-spore formation in still another mildew; letters as in 1. 5. Thread of a downy mildew (Peronospora leptosperma) bearing spore-like swimming- spore-cases (s). All highly magnified. After DeBary. Downy mildews and their allies (Peronosporinece in part). Long ages ago, when the fungi had developed the saprophytic and parasitic habits, as one sees in the damping-off fungi, it became advisable to abandon the aquatic life because more op- portunities are presented in aerial conditions. The damping-off fungus shows some such tendency but the blights or downy mildews show it still more clearly, for most of these fungi are no Minnesota Plant Diseases. parasites on common garden plants. It is a noteworthy fact, however, that they still require very damp atmospheres in which to develop well and only become epidemic in excessively moist seasons. These fungi have a very well developed system of threads which are much branched and spread through the tissues of the host plant. They are provided with little sucker- threads which penetrate the cells of the host plant and often form here very densely branched systems of threads. These sucker organs steal the nutrient material from the host plant. It is moreover a robber method similar in some respects to that of the damping-off fungus, for the host-plant parts attacked are ruthlessly and almost immediately killed. Such is the com- mon effect of potato blight or downy mildew of vines. On the other hand, these fungi show more power of selection than do the damping-off fungi. Some are capable of attacking differ- ent and even distantly related plants but in general a given fungus of this group is quite constantly found on the same host or on closely related plants, e. g., members of the same genus or family. Wherever the threads of the fungus become abundant, the host plant is killed. The ancestral aquatic habit of these plants is still retained in the method of distribution by spores for these are swimming spores. Hence the fun- gus can spread rapidly only when there is a great abundance of moisture, as during excessive rains and cloudy, misty days. Under such conditions the swimming spores spread rapidly in the water drops and may be carried in these drops from plant to plant. An epidemic may thus result. On the other hand, these fungi have learned terrestrial methods of spore distribu- tion. We find upon a close examination of the area infected by a potato blight, or false mildew, at first a thin grayish or whitish haze or shimmer spreading over the leaf, and that this fine mold-like growth is caused by an enormous number of usually much branched threads which come out of the air pores of the leaf. They pinch off of each branch end small, round, pear- or lemon-shaped bodies which look very much like spores and are commonly so-called. These bodies are light and easily carried by the wind and thus alight on other plants. In the potato blight and some of its allies this spore-like body does not betray its real nature until the conditions of moisture are Minnesota Plant Diseases. 1 1 1 favorable. Then it shows itself to be a spore-case and forms internally numerous swimming spores, which escape and spread the disease. Some of the downy mildews, however, have learned still more thoroughly the terrestrial habit and have al- most entirely forgotten the ways of aquatic fungi. In these the spore-like body really acts as a spore, grows out directly into a thread and does not develop swimming spores at all, although in some forms it starts out as though it were going to form them and then abandons the attempt. We have here an excellent example of the persistence of a habit even after it is FIG. 45. — A Downy mildew with the aspect of a white rust. Under surface of burweed elder (Iva xanthiifolia) showing dense clusters of spore-like spore-cases. Original. ill adapted to the plant's new methods of life. Egg-spores are also formed throughout this group, though in a few cases, as in the common potato-blight, they have not yet been ob- served. As in the damping-off fungus, the breeding act of many forms has actually been demonstrated. The egg spores are typically resting spores and, as in the damping-off fungus, serve to tide the plant over winter or other unfavorable sea- sons. They are usually found in abnormally swollen parts of the host. The plants of this group are all parasites and most of the known forms attack cultivated garden plants. They live 1 1 2 Minnesota Plant Diseases. chiefly in the leaves where, in the roomy air-spaces, which are charged with moisture, they realize most nearly their prefer- ence for moist conditions. Perhaps the most famous fungus in this group is the potato blight, which causes rot of the plant in the field and a dry brown rot of the tubers in the cellar. Epidemics of this disease follow excessively moist and warm seasons and have been known to cause great damage. Toma- toes and other plants of the potato family also suffer attack from this fungus. Another very famous fungus of this group is the downy mildew of vines, which attacks the vine foliage and fruit, both of the old and new world, and causes great dam- age. Others exhibit habits similar to damping-off and attack seedlings. Some are found on bean plants, on grasses, and a very conspicuous one inhabits members of the carrot family. They are also found on sun-flowers and again a very impor- tant one is known on melons and cucumbers and their allies. Lettuce, beets, clovers, onions and tobacco plants, besides a large number of wild plants, as violets and anemones, are known as hosts to these parasites — in fact, almost every family of plants has its downy mildews. (Figs. 2, 39, 40, 44, 45, 166 to 171, 196 to 198.) White rusts (Peronosporincce in part). Very closely allied to the downy mildews are the white rusts. In their egg-spores and general habits they are quite similar. Just as in the potato blight, spore-like bodies are produced which later show their spore-case nature, but these spore-cases are not cut off singly from the ends of threads. They are formed in chains and these chains are arranged together in such dense clusters that they form a white rust-like mass when the host-plant skin has been broken and thrown back. The most abundant of the white rusts is one common on the weed plant known as shepherd's purse, and found also on other mustards. Another is found on pig weed and on portu- laccas, others on morning glories and on a great many other plants. As in the downy mildew the egg-spores are often found in swollen portions of the host where the fungus has excited the host plant to unusual effort. The advantage to the para- site is evident, since it is in the egg-case-producing part of the plant that much nutrition is needed. (Fig. 45.) Minnesota Plant Diseases. Black molds (Mucorinccc in /art). These fungi are exceed- ingly common plants found on starchy materials and hence often called bread molds. Although they have descended from water-inhabiting plants they have retained almost no trace of an aquatic habit, with the exception of the requirement of a moist atmosphere for growth. That is to say, there is no formation of swimming spores ; for all of the spores, except the resting spores, are distributed by the wind, though aided in some cases by a special explosive apparatus. The spores, as in other algal fungi, are of two kinds, viz. : the egg spores and those produced without breeding. The former are formed by a different method from that of the false mildew where an egg and a differently shaped male thread branch are found. In the black molds both breeding organs are alike in size and shape and are indistinguishable, just as is the case in the pond scums among the algae. The egg spore is a resting spore and is provided with a large, thick, resistant, usually black-colored coat. However, the most common form is that of the non- sexually produced spore. These are produced in tiny, black, spore-cases, which appear like small, black points in the mass of mold threads. Each case contains a great number of spores which escape by the breaking of the spore-case wall and are blown about in the wind. In some molds, which are particularly abundant on horse dung, there is a swell- ing in the thread just below the spore case and this swelling acts as a syringe bulb under pressure. When the spores are ripe the whole spore case contents _ FIG. 46.— A black mold. are blown off at once and thrown a half- foot or more into the air. The black molds are of very great im- portance on account of the damage which they cause to food stuffs, particularly the starchy foods. Bread, cake and pastry, when kept moist, will almost surely develop mold, because mold spores are to be found in the air of almost any region and at almost any time of the year. The black molds are all typically The black spore-cases are seen on the ends of the fungus threads. Highly magnified. After Zopf. ii4 Minnesota Plant Diseases. saprophytes. A few have, however, learned just the beginnings of parasitism, e. g., those black molds which attack ripe fruits through wounds or thin skins. Since the protoplasm in fruits is in a dormant condition and contains an enormous amount of food material, sugar, etc., the black mold is able to live here, amateur though it may be, as a parasite. Some animal dis- eases have already been mentioned as the result of black mold, though in these cases it is doubtful whether the fungus is actu- ally parasitic, or merely saprophytic. It has in recent years been found that some molds have the power of changing the starchy material into sugars and adepts in this process have been selected and are now used to convert potato starch into sugar; from these sugar solutions, by the action of yeast, alco- hol is then produced. In this process the potato starch is ster- ilized by heat and enclosed in perfectly clean casks, and the fun- gus is then introduced under perfectly clean conditions. When the starch is all converted, the yeast is introduced, also in the pure state, so that the whole process is as carefully conducted as in the culture of bacteria by an expert bacteriologist. By this process the yield of alcohol has been enormously increased. Moreover, some black molds when submerged in a sugar solu- tion have the power of forming alcohol and carbonic acid gas just as do the yeasts ; but they are not vigorous enough to be of economic use. Some of the peculiar intoxicating drinks of Asiatic tribes are produced by the introduction of certain black molds and yeasts into starch mixtures. Many black molds are also to be found on decaying fungi, as mushrooms, though it is not certain that they are actually parasites, they undoubtedly hasten the decay. (Figs. 14, 16, 17, 46.) Black-mold parasites (Mucorinea in part}. Closely related to the true black molds are certain forms which live chiefly as parasites on other black molds. They are also found on a few other fungi. If a piece of bread with an abundance of black mold on it be left in moist conditions for some time these parasitic molds almost always appear. They are very minute plants and require high powers of the microscope for their observation. They form a delicate thread mycelium from which fine branches Minnesota Plant Diseases. FIG. 47. — An insect mold. (Fly chol- era fungus.) 1. A cluster of threads with spores cling- ing to hairs on the insect's body. 2. Fungus threads from the fat-body of an insect. 3. Spore -bearing threads, highly m a g n i fi e d. 4. Above, a single spore; below, germinating spore, forming a sec- ondary spore. Highly magnified. After Brefeld. are sent into the threads of the host plant where they obtain nourishment for the para- site. They are also found on certain of the blue-mold group of fungi. Insect molds (Entomophtfiorinea). Of all the algal fungi these are most clearly non- aquatic in their habits. Like the black molds they form breeding spores, from similar sex organs, though these spores are not of fre- quent occurrence. On the other hand the non-sexual spores are very abundant and are pinched off from the ends of special threads. Moreover, there is usually some de- vice for throwing the spore to a distance. The thread is swollen just below the spore and when the latter separates from the thread the release of pressure in the swollen portion results in the forcible ejection of the spore. This is the case in the common fly cholera fungus. Most of the insect molds are para- sites on insects either in the adult stage, as in the fly cholera, or on the larva. When the fungus has gained entrance to the body of the insect it soon kills the latter and then lives saprophytically, pro- ducing a great abundance of spores. House flies are commonly attacked by fly cholera in autumn and when they die cling tightly to window panes and other objects. They are soon surrounded by a halo of spores thrown onto the pane from the fungus threads by means of the spore-throwing device described above. Many other insect diseases are caused by these fungi. Caterpillars some- times become covered with moldy growths which completely envelop them. From the surface of these growths are thrown the fungus spores. These parasites of insects prove of great benefit to plant growers ii6 Minnesota Plant Diseases. because they destroy so many insect pests of plants, as lice, lo- custs, etc. They are also responsible for some destruction of such common pests as mosquitos. Some insect molds are sap- rophytes living on dung and are apparently of no economic im- portance. A few attack plants and particularly the sexual plants of ferns when cultivated in greenhouses. They cause a disease similar to damping-off. The economic advantages of this group, however, far outweigh the injuries. (Figs. 14, 47.) Chapter IX. Fungi. Kinds of Fungi* Sac Fungi. JS Sac fungi (slscomycetes). The second of the three great groups of fungi is that of the sac fungi and this group is in short easily distinguished because all of its members bear at least some of their spores inside of sacs. These sacs may be spherical or pear-shaped or long-cylindrical, according to the plant, and they always contain a definite number of spores. The sacs in the simplest of these fungi are borne irregularly upon the loose weft of the mycelium but in the very great ma- jority of sac-fungi they are borne in capsules of various shapes and often of great complexity. Sometimes these capsules are little, black spheres, as in the powdery mildews, with or without an opening, while in others they may be borne in the fruiting bodies known as truffles or in the cups of cup-fungi. According to our present knowledge a breeding act seems to precede the formation of the sacs and in some cases one, in others, numerous, sacs may arise as the re- sult of a single breeding. A vast number of sac fungi form more than one kind of spore — in fact many produce two or three so-called accessory spores, so that the study of such forms becomes a very difficult matter. Indeed, one may find many of these accessory forms without the main sac-form and it is then often exceedingly difficult or altogether impossi- ble to even determine the fungus. Thousands of such fungi have been found — many causing important diseases of plants— which are thus imperfectly known and are described un- der provisional names until more facts are discovered about their life-stories and their proper sac forms. Not until then can they be accurately and permanently classified. Such fungi are called imperfect fungi. It is even probable that many have for- gotten how to form their sacs and now produce only the acces- sory spore-forms and thus present an actually imperfect life- u8 Minnesota Plant Diseases. story. Again, the sac spores may be of such seldom occur- rence that they have been entirely overlooked. Conspicuous examples of accessory spore-forms are seen in the green mold growths of cheese, in the powdery mildews or summer spores of the mildew fungi and in the honey-dew spores of the ergot. The groups of fungi discussed in this and the following chapter are subgroups of the sac fungi. (Figs. 10, 14 and below.) Yeasts and their allies (Saccharomycctcs). Undoubtedly the simplest of all of the sac fungi, at least as far as structure is concerned, are the yeast fungi, though this simplicity is to be explained by a reduction from a more complex form, due to peculiar habits. The yeast plant consists of a single sphere- like or somewhat elongated cell, so small in size that high powers of the microscope are necessary for their examina- tion. These cells multiply rapidly by bulging out little spherical "buds" which be- come separated from the par- ent cell and soon produce new buds in their turn. A cell may continue to bud off little plants as long as nutrient ma- terial is available. Sometimes the daughter cells do not sep- arate from the mother cells completely but remain more or less loosely attached and thus false filaments or threads are built up. Such are often found in the scums on the sur- face of yeast-containing fluids. The simple method of propa- gation by budding suffices the yeast plant for multiplication during favorable conditions and the ordinary yeast-plant-cell is often, moreover, capable of re- sisting successfully very unfavorable conditions. But when FIG. 48.— Yeast fungus cells, a. Ordinary bread yeast, showing sprouting vegeta- tive cells. b. Spore formation in a yeast; four spores in a sac. Below are shown four free spores. Highly magni- fied. After Rees. Minnesota Plant Diseases. 119 their nutrition runs low, yeast plants may prepare for unfavora- ble seasons by forming sac-spores. A breeding act has been described for at least two kinds of yeasts, preceding the forma- tion of the sac-spores. The two plant cells which unite are both similar, and inside of the united cell four spores are formed. In most yeasts, however, no breeding act precedes the formation of sac-spores. The sac-spores have thick walls, are resistant and are often capable of resting for a long time before resuming growth. Yeast plants are, in general, found growing most vigorous- ly in liquid solutions of nutrient material for the budding habit is of peculiar advantage in such an environment. The daughter cells are easily separated from the mother cell and are carried by convection currents to other parts of the liquid where they get more nourishment. It is in sugar solutions or in closely allied substances, as starch, that the yeasts thrive best. In nature they are found in the juices exuding from ripe grapes or other fruits. Many yeasts possess the power of breaking down the sugars into carbonic acid gas — which escapes in the form of bubbles — and into alcohol; i. e., they have the power of fermentation. This process is made use of in bread-making and in beer and wine making. In the former the carbonic acid gas is used in the raising of the bread while in the latter the alcoholic products are those sought for. Not all yeasts have the power of fermentation and many, although possessing this power, are not vigorous enough to be of commercial use. The common beer and bread yeasts have been chosen because they are vig- orous fermenters. Moreover, many yeasts can ferment only certain kinds of sugars, as milk, or cane or grape sugar. One may also find several kinds of yeasts which, as far as structure and appearance is concerned, might be considered identical but which show that they are different in their powers of fer- mentation. Yeasts also play an important part in the produc- tion of many drinks of far eastern peoples, as of Japanese "saki," of kefir and kumys, though in these cases certain bac- teria and blue molds may aid in the process. In the produc- tion of by-products, singly and in combination, yeasts may differ in the quality or tastes of the liquors thus produced, and 120 Minnesota Plant Diseases. the custom now obtains in some breweries of using only pure cultures of yeasts of a known kind, thus insuring uniform re- sults. Certain wild yeasts and bacteria may find their way into the brew and by the formation of peculiar compounds may spoil the flavor. It has already been mentioned that certain yeast-like fungi cause several diseases of lower animals as well as thrush and sore throat in children. The systematic position of these fungi, however, is uncertain at present since the sac- spores have not been found. The power of fermentation is not confined exclusively to the yeasts since other fungi, though not many, possess this power, and it is possible that the thrush fun- gus is a member of some other group of fungi. As far as is known at present no yeasts can be said to cause undoubted parasitic disease in plants. It must be remembered, however, that in the exuding sugary juices of fruit under natural condi- tions, or from wounds, yeast cells are very commonly found, and it is not inconceivable that they work their way into the fruit and assist in fruit rot. (Fig. 48.) Slime-flux fungi (Endomycetacea). In the slimy exudations which often flow from wounds in trees a great variety of such organisms as bacteria and fungi abound, and among them a close relative of the yeast fungi is not uncommon. This fun- gus differs from the yeasts in always possessing a thread myce- lium and forms its spores on branches of this mycelium. It is not certain whether or not this fungus is the cause of the flux or whether it simply finds in the flux congenial conditions and appropriate food. Leaf curls and plum pockets (Exoascacea). These fungi are of frequent occurrence on plants of the plum family such as domestic plums and cherries and peach plants. The host plant part is usually swollen. Leaves thus affected sometimes curl much and become distorted. Plum and cherry fruits when at- tacked by the fungus form the well-known "pockets" without stones. Both pockets and curls bear the spores of the fungus in a layer which covers the whole or a considerable part of the affected organ. This region takes on a greyish white color which is due to the presence of a great number of short cylin- drical sacs, each containing eight spores. The spore-sacs stand side by side, like posts in a palisade, upon the surface of the Minnesota Plant Diseases. 12 I leaf or pocket, and at right-angles to its surface. They arise just under the cuticle which is pushed up and sloughed off as the spore-sacs ripen. No breeding act has been seen to pre- cede the spore-sac formation. The sac-spores are often capa- ble of budding in yeast fashion when placed in sugar solutions, and in some of the fungi they bud in this fashion before they are released from the sac so that the latter may then contain a large number of spores. In addition to the effect upon fruit and foliage of plums, these fungi often cause witches'-brooms on cherries and plums as well as on birches and alders. Oaks, FIG. 49. — Plum-pocket fungus and loose- we ft fungus. 1. A loose wefted collection of spore sacs, which is surrounded by barbed threads. A loose-weft fungus. 2. A small group of threads from 1, bearing a number of sacs. 3. Same as 2, showing a single sac with its sac-spores. 4. Plum-pocket fungus. Shows the spore-sacs of a pkim- pocket fungus arranged in a palisade on the surface of the pocketed plum; c the cells of the plum; m fungus threads and h the fungus spore sacs. All highly magnified. 1, 2, 3 after Sachs; 4 after DeBary. poplars and cottonwoods and sumacs are also attacked by them. (Figs. 49, 193.) Loose-weft fungi (Gyuinoascacccc) Very closely related to the slime-flux fungi are the loose-weft fungi. The spore sacs are borne in dense clusters on a very loose weft of threads and in no regular arrangement. In some, there is a loose system of threads surrounding the cluster, forming a covering not un- like a large-holed basket. These threads are also usually armed with tiny spines. Such a covering is merely an ama- teurish, spore-sac capsule. The loose-weft fungi are peculiar in their habits. Many are found exclusively on feathers. 122 Minnesota Plant Diseases. some on bones, some on bees' nests, while others seem to pre- fer animal remains and meat extracts. They are not, however, either conspicuous in number or in size. (Fig. 49.) Green and blue molds (Aspergillacea). The blue and green molds are amongst the best known and most conspicuous of fungi. They are the great destroyers of food stuffs and as such are well-known to every housewife. The common green or blue mold is an accessory spore stage. In this form thousands of threads stand upright side by side, each branches very pro- fusely in broom fashion and each branch terminates in a long row of pinched-off spores which are of the characteristic green color. Millions upon millions of these spores may be produced by a small patch of mold. Such mold spores are present in great quantities in the air at almost any time of the year, so that just as soon as any food-stuff is exposed to the air it may be sown with green mold spores. These will quickly germi- nate and will produce in a very short time — often in a few days —another crop of mold spores. The green-mold spores, though the most common, are not the only spores produced by these fungi. There is also a sac-spore, though in most forms it does not occur frequently — in fact it is usually rare. These sacs are spherical as in the loose-wefted fungi, but are found on threads tightly woven together, and the whole spore-sac mass is surrounded by a membrane-like wall or covering, which is formed by closely united threads. These sac-capsules are often yellowish or black and are seldom larger or even as large as a pin-point. They are usually tiny spheres and of a solid structure. The spores, when ripe, are released by the de- cay of the capsules. There is no definite arrangement of the sacs in the capsule nor is there a special opening through the capsular membrane to allow of the escape of the spores. In some forms, at least, a breeding act precedes the formation of the capsule. The green and blue molds are especially fond of bread and other starchy materials, preserves, etc. They are also found on cheese and some varieties of mold are used to ripen the cheese, where the flavor is largely due to the green mold present. They are frequently found in preserved fruits and jells and also as simple parasites, causing mold-rots of fruits. (Figs, i, 1 88, 189.) Minnesota Plant Diseases. 123 Allies of green and blue molds. There are numerous allies of these molds which have strange habits indeed. Some, as in the loose-weft fungi, live on feathers and some live on the horns and hoofs of cattle. These fungi are of comparatively rare occurrence and have not yet been collected in Minnesota. Others, however, which resemble the powdery mildews in many respects, are found on the leaves and twigs of living plants, though seldom assuming a destructive parasitic habit. False truffles (Tcrfcziacece). As is well known, the truffles are underground bodies resembling, to a small degree at least, small potatoes in appearance. Now the false truffles are very similar to the true truffles in appearance but they differ in some characters. The spore-sacs are not arranged with the same regularity which is common in the true truffles but are found in a loose weft as those in the loose-weft or blue-mold fungi. They may, in fact, be considered as huge underground spore- sac capsules of blue-mold-like fungi. Some of these false truf- fles are apparently the producers of fungus root-hairs in some flowering plants. They have not yet been collected in Minne- sota. Black fungi (Pyrenomycetinece). These fungi constitute an enormous group of plants. They all agree in having a spore- sac capsule in which the spore-sacs are arranged in definite or- der and arise from the bottom of the capsule. The latter are usually, but not always, black in color and often resemble burnt wood. The spore-capsule in all, except the powdery mildews, has a definite method of opening by means of a pore which is sometimes protected by spiny processes. The simplest forms, the powdery mildews, are very similar in many respects to the blue and green mold plants and are their nearest relatives. Like these molds the black fungi possess accessory spore-forms and those of the powdery mildews, constituting the summer spores, are particularly like the green mold spores of the green mold fungi. They are not, however, green in color. The black fungi are conspicuous in the great number and variety of accessory spore-forms. Some species alone possess three or four kinds of such spores in addition to the sac-spores. The common Minnesota forms of the vast number of plants in this group can be arranged in the following ten groups. I24 Minnesota Plant Diseases. Powdery mildezvs (Erysiphacece). The mildews constitute the simplest group of black fungi. The mycelium is usually to be seen on the surface of leaves as a white, moldy covering. The threads send branches into the skin cells of the host and there absorb their food and live parasitically, but the main my- celium of the fungus never lives inside of the host. In the rBi m FiG. 50. — A powdery mildew on common plantain leaf. The powdery coat of the threads and the small black fruiting bodies can be clearly seen. Original. summer, spores are produced in enormous numbers and form a dust-like covering over the leaf, whence the common name of powdery mildew for this group of fungi. These spores are pinched off in rows from upright threads, which thus become converted into chains of spores. Towards fall there arise, on the Minnesota Plant Diseases. 125 mycelium, minute spheres about the size of a pin point. They are at first white, then become yellow and finally dark brown to black. They are the sac capsules and bear one or more spher- ical or pear-shaped sacs with two to eight spores in each, ac- cording to the species. The capsular wall has no special meth- od of opening but it may often possess elaborately-shaped threads known as appendages, which are often much branched and form a crown or circle around the case. Such may as- sist in the distribu- tion of the who1e (/ *sKS spore-sac capsule. The powdery mil- dews live entirely on the outside of leaves and young branches of plants and are often d a n g e r o u s parasites. A great number of our com- mon garden plants as well as wild flow- ers are attacked by some sort of pow- dery mildew, though the conditions are FIG. 51.— The fruiting body of the powdery mildew of black haw, showing the appendages. The sac-capsule has been broken and the sacs, each with about eight spores, are emerging from the split. Highly magnified. Microphotograph by E. W. D. Holway. not usually such as to create epidemics. Roses and grapevines are conspicuous suf- ferers as are also gooseberries and other garden plants. These fungi are also found abundantly on lilac bushes, all kinds of wil- lows, birches, poplars, elms, oaks, maples, and many others, but on these do not often cause much damage. (Figs. 10, 50 to 52, 134, 135, 152, 192, 202 tO 204, 210.) Honey-dcic fungi (Pyrcnomycctinccc in part). Structurally this group of fungi is a close relative of the mildews. The spore-sac-capsule is built on the same general plan but does not usually contain appendages while, on the other hand, it is usually furnished with a pore for the exit of the sacs and 126 Minnesota Plant Diseases. spores. Accessory spores are also found in abundance in these fungi, many being enclosed in special capsules similar in ap- pearance to the sac-capsules. The mycelium is, moreover, often black. Many of these fungi live on leaves but not in a typically parasitic fashion. They thrive well on the excretion of certain insects and since such excretions are found abun- FiG. 52.— The fruiting body of the powdery mildew of willow, showing the appendages and spore-sacs. The latter have "been forced out of splits in the sac-capsule. Highly mag- nified. Microphotograph by E. W. D. Holway. dantly on the leaves of plants these fungi are also found on the surface of the leaves. On account of the abundance of myce- lium produced and on account of its dark color a vigorous growth of mycelium may exclude sunlight from the leaves and thus injure the leaf, although the fungus may not in itself be harmful. These fungi are often known as the sooty molds on account of the soot-like mycelium which is developed. Minnesota Plant Diseases. 127 FIG. 53. — Ergots of grasses. On left is one on a reed-grass; on right one on quack-grass; s sclerotium or "ergot," the fungus storage organ. Original. 128 Minnesota Plant DiseaseSo Ergot fungi (Hypocreacece in part). The fungus which pro- duces ergot is a member of the black fungus group, though not a very close relative of the mildews. The life-story of such a fungus is somewhat com- plex and we may illus- trate by that of the ergot of rye. In the summer, youngest FIG. 54. — Ergot fungus on canary grass; s sclerotium or storage organ of the fungus. Original. sticky solution and in their visit when the grains are to fill, or just before that period when the grass flower opens, the spores of the ergot fungus may lodge in the flower and start to grow. The young threads are capa- ble of attacking the grow- ing grain and in a short time almost completely absorb the latter, form- ing a more or less soft, spherical or elongated mass of mycelium, at the summit of which are formed, in convolutions of the surface, thousands of summer spores. These are accessory spore- forms. The production of these spores is accom- panied by the formation of sweet saccharine fluids which are very attractive to certain insects. Visit- ing insects become at least partially covered by summer spores in the to other flowers transfer these spores, just as they do the pollen, from flower to flower. Minnesota Plant Diseases. 129 Now it is only in the young stages of the flower that these spores can attack the grain so that rapid spread of spores is necessary and is, moreover, readily accomplished by this insect- method of spore distribution. These spores are produced by the fungus for some time. Toward the time of ripening of the grain, the production of summer spores ceases and the fungus commences to pack up reserve nutrition in its threads. These are now compacted together in a very solid mass the exterior of which turns violet black. The whole structure becomes a storage organ or sclerotium, and often requires a rest period be- fore it will develop further. In this sclerotium nutrient mate- rial is found in the form of fungus starch and oils. Certain vio- lent poisons are also found in them and are extensively used in medicine, for this storage organ is known in pharmacy as the drug "ergot." Of just what use to the fungus these poisonous compounds are is not quite clear. Possibly they tend to pre- vent the consumption of strongly ergotized grains, thus avoid- ing destruction by feeding animals. In the spring time, after their winter rest, the ergots are capable of further growth. When placed in proper conditions of moisture and temperature they send out small cylindrical stalks which bear tiny spherical heads about the size of small brown mustard seeds. These little heads become blackish in color and bear the sac spores. They are not, however, single sac-capsules but, if one examines the surface of this sphere, one finds a large number of little openings and, upon further inves- tigation, these openings are seen to connect with pear-shaped cavities just beneath the surface. Each of these cavities is in reality a spore-sac capsule. In other words, the spore-sac cap- sules have been aggregated together onto a common surface and produced in abundance on account of the great amount of available storage material in the ergot. In each sac capsule are numerous very long, cylindrical sacs, and each sac contains eight long thread-like spores, which have already been divid- ed by cross-walls into about sixty-four cells. These cells sepa- rate very readily and each is capable of growing out into a my- celium, so that each sac contains about five hundred spore cells. In addition to the spore-sacs there may be long, swollen threads in the sac-capsule, which aid especially in discharging Minnesota Plant Diseases. the spores and sacs from the capsule. The spore-cells or the honey-dew spores may be carried to another flower and thus the life-story is recommenced by the new infection of the grain. The ergot fungus is common on a great many grasses and particularly upon cultivated species as wheat, rye, barley, etc. It is found very abundantly upon wild rice in many places and is also abundant on grasses growing on railroad right-of-ways. (Figs. 53 ^ 55. X54, iS5-) FIG. 55. — Fruiting bodies and spores of the ergot fungus. 1. Young ergot in honey-dew spore stage. 2. Small section of the top of 1, showing summer or honey-dew spores. 3. A germinated ergot with sac-capsule-bearing clubs. 4. The end of one of the clubs in 3. 5. Section of 4, showing capsules at surface of head. 6. An enlarged view cf a capsule, showing arrangement of sacs. 7. A single sac showing long, thread-like spores. 1, 6 and 7 highly magnified; 4 and 5 of medium magnification. 1-6 after Tulasne; 7 after Brefeld. Caterpillar fungi (Hypocreacece in part). A very close rela- tive of the ergot fungus is the caterpillar fungus, the habits of which have already been described in a previous chapter. Spores of the fungus send out germ threads which penetrate the hard coat of the caterpillar or grub and, feeding on the soft Minnesota Plant Diseases. parts of the insect-body, build up a mycelium which consumes all of the interior of the host except the chitinous skin. It thus stores up an enormous amount of nutrient material in the form of a storage organ or sclerotium, which is an exact cast, not only of the external form of the insect but also of the in- ternal organs. When this storage organ has rested for some time, and when conditions of moisture and temperature are favorable, it sends up, usually one or more, rarely two, stalks, which come above ground. Here they form a club-s h a p e d, bright-orange - colored body which may easily be mistaken for a club fungus. Close exam- ination sho\vs this body to contain nu- merous small holes just as in the head of the stalk on the germi- nating ergot, and these holes again communi- cate with pear-shaped cavities, which are the s p o r e-sac capsules. The sacs also contain eight long, thread- shaped spores, divided into numerous cells, each of which is able to form a germ thread and thus infect other grubs or caterpillars. Sometimes the storage organ does not produce a sac-capsule-bearing stalk, but produces in one of several ways a great abundance of accessory spore forms which are pinched off from threads in enormous numbers. This happens if one places a freshly developed storage organ in a moist chamber, or it may happen in nature w7here one finds frayed-out branches or strands from the storage organ FIG. 56. — A caterpillar lungus. The insect-shaped bodies are fungus casts of threads which form a storage organ ; raising from these are club-shaped bodies which are covered above with fine warts. These warts are the tops of the sac-spore-capsules. Original. 132 Minnesota Plant Diseases. giving rise to a dust of white spores at the sur- face of the ground. These spore-forms have all been described as of separate and independent plants. They seem to be able to infect the insects just as do the sac- spore cells. These fungi are thus seen to be very similar to the er- got fungus in all essentials but the accessory spore forms are more numerous and are found under dif- ferent conditions than are those of the latter. (Figs. 10, 15, 3i, 56.) Strangling fungi (Hypocreacece in part}. On a few grasses in the state occurs a fun- FIG. 57. —A strangling fungus on grass leaves and s t e m s. A few leaves extend above the fungus fruiting body, but the growth of the host is usually stopped. The surface of the fun- gus fruiting body is covered with warts which are the ends of the spore-sac-capsules. Original. Minnesota Plant Diseases. 133 gus which is closely related to the last two groups of fungi and particularly to the caterpillar fungus. This fun- gus exerts a strangling action on the host plant. It appears as a whitish or light-tan-colored ring around the young leaves at the tip of the plant. The threads soon form a solid mass en- closing the young leaves and pre- venting them from unfolding. The branch on which the fungus is thus formed may ultimately die off. When the fungus has in- creased somewhat in thickness the sac-spore capsules make their ap- pearance as pear-shaped cavities on the surface of the fungus, just as on the clubbed stalks of the caterpillar fungus. The sacs and spores are also similar to those of this fungus in appearance. The accessory spore- forms appear on the fungus preced- ing the sac-spore forms. The life story in this fungus is thus seen to be simpler than in either the ergot fungus or the caterpillar fungus. No storage organs are developed. (Figs. 57, 58.) Other allies of the caterpillar fun- gus (Hypocrcacca in part). Very commonly on the milk mushrooms are found fungi which cause the abortion of the gills of the host and which spread themselves out all over the latter, covering it with a bright red-orange color. On the surface reddish wart-like bodies can be seen and these are the spore- capsules which, as in the caterpillar fungus, open by pores to the sur- face. The sacs are also of a similar shape but the sac-spores are not as long. FIG. 58. — A strangling fungus. 1. A grass stem with a fungus fruit- ing body, part of which has been removed, showing the sac-spore- capsules in position. 2. A single sac, showing long thread spores. 3. A single spore. 2 and 3 highly magnified. 1 after Winter: ? and 3 after Brefeld. 134 Minnesota Plant Diseases. Bright colored stick-fungi are also allies of these fungi and are very common on dead poplar or cottonwood sticks. On the latter, cushions an eighth to a quarter of an inch in height and breadth, are formed by the fungus and on the surface of the cushion arise the accessory spores in great abundance. After a time these spores cease to form and there is now pro- duced from the same surface, supplanting the accessory spores, the sac-spore capsules of the fungus, which are again pear- shaped cavities with pore-like opening to the exterior. The sac-spores are -short and rounded at the ends and two-celled. Some of these fungi are wound-parasites attacking orchards and timber trees through storm or hail-wounds, etc. They are sometimes known as red knot. In some of these fungi still other kinds of spores and spore-bearing organs are encountered. Chapter X. Fungi* Kinds of Fungi* Sac Fungi. Black knot and allies (Dotliidcacccc in part). One of the most conspicuous fungi of Minnesota is the so-called black- knot fungus of cultivated and wild cherries and plums. In the mature stage of the fungus, its host-plant branches carry black knot-like swellings and distortions, which are very conspicuous. These knots so interfere with the nutrition of the branch beyond that the latter usually dies off in a year or two. The fungus then gradually works its way downward to the intersection of another branch, when this is in turn killed off. The mycelium, which lives inside of the bark, causes an increase in the thickness of the latter, followed by a splitting lengthwise. There is also a swelling of the un- Etv deriving wood and the fungus feeds upon this swollen, soft mass. It builds up a dense mass of the mycelium on the outside of the branch. This mass when it first appears is a light-yellow- brown and forms on its surface numerous sum- mer spores which rapidly spread the disease. These spores are pinched off of the ends of short upright threads and are produced during the summer. In the fall the mycelial mass becomes FIG. 59.-Biack knot darker until it is jet black. It looks not unlike rightL1 u ^oSaT charcoal. In this mass are formed numerous tiiee su7facTrma?k pear-shaped sac-capsules over the entire surface. These capsules open by minute pores to the ex- terior so that in the spring the surface of the knot appears to be covered with tiny warts, each wart indicat- ing a spore-sac capsule. capsu?edss °f A f t 136 Minnesota Plant Diseases. The sacs are long cylinders and contain eight spores, each of which is made up of one large and one small cell. The sac spores are shed in the spring and can infect new branches or other trees. Almost all of our plums and cherries are subject to the attack of this very dangerous fungus and in the wild plants it is often found in very great abundance. It has proved a dangerous pest to cultivated plants, and in many places in the United States has ruined whole orchards and rendered aid by state laws necessary for protection. Another very common disease which is a close relative of the black-knot is the fungus producing black spots on a great many grasses both wild and cultivated. These spots are formed on the leaves and are often mistaken for black rusts, but they can easily be distinguished from the latter diseases by the fact that the skin of the host is not split open in long lines and the spores are not produced in the way well known for rusts. The spores are formed in sacs borne in small spherical cavities or capsules. These appear in clusters at the surface of the black spots just as they are found in black-knot. The fungus is often very abundant on grasses. In such cases they undoubtedly levy a considerable tax on the starch-making apparatus of the host and thus impoverish the latter. Similar spots are produced on the leaves of elm trees. The leaves of the common white elm are often found almost com- pletely covered with such spots. The capsules and sacs are produced in a manner somewhat similar to that in the black spots of grasses and, though never seriously threatening the life of the elms, undoubtedly steal much nourishment from them. These black spots must not be confused with the tar spots of maple and willow which are different diseases. The latter are also sac fungi but belong to the cup-fungus group. Superficially these fungi resemble each other; in the black spots of grasses and elms, however, the sacs are found in pored cap- sules while in the tar spots they occur in cups. (Figs. 19, 59, 191.) Dung fungi and their allies (Pyrenomycetinece (in part) including Sordariaccce and Chatomiacece). If horse dung be placed in a moist closed chamber and allowed to remain un- disturbed for a week or two there will almost invariably arise Minnesota Plant Diseases. 137 dense crops of very small, black, thickly-crowded, pear-shaped bodies. These often bear crowns of dark tangled hairs surround- ing an opening at the tip. They are sac-spore capsules and dense masses of spores can be seen collected near the opening or scattered as a dense brown or black dust around the capsules. The latter are formed singly and some- times but not usually up- on mycelial masses, as is the case in black knot, cat- erpillar fungus and ergot. The spores occur usually eight in a sac and often have curiously-shaped tail- like appendages. These fungi (Sordariaceas) are very abundant and at first sight seem insignificant but are of some importance nevertheless. The dung of horses is made up largely of the indigestible woody parts of plants, e. g., the veins of the leaves of grasses, and it is on these that the fungus feeds, disintegrating them as wood-destroying fungi do timbers. Another group of forms (Cbsetomiaceae) closely allied to the dung fungi is found chiefly on moldy paper. Here the sac cap- sule is provided with great twisted and tangled masses of crown hairs in which the spores are lodged after ejection from the sacs and sac-capsules, and are later from this point shaken out and distributed. Building paper is often rotted by these fungi. (Fig. 60.) Sphere-fungi and their allies (PyrenomycetinecE (in part} in- cluding Sphceriacece and other families). .This is one of the very largest groups of fungi, rivalled in point of numbers only by the mushroom allies and cup fungi. It is also of great impor- FIG. 60 ove is seen a sac-capsxile of a dung fungus (Sordariaceae) showing the escaped sacs, which are cylindrical and contain each eight spores. Broken sacs and free sac-spores are also seen. Below are two sac-capsules of another fungus of this group (Chaetomiaceae); At the summit of the fruiting body are seen great tangles of twisted threads in which the spores are caught. Magnified. Microphotograph by F. K. Butters. 138 Minnesota Plant Diseases, tance economically 'because of its numerous diseases. The sphere fungi are close relatives of the dung fungi and build similar sac-capsules which are usually tiny spheres. These are generally formed singly or are sometimes grouped on a mycelial cushion somewhat similar to black knot. The sac-capsules are very often microscopically small. These fungi are remarkable for the great numbers and variety of accessory spores produced. Most of the so-called imperfect fungi are undoubtedly merely accessory spore-forms of these fungi. Although the group is a large one the sac-capsules agree to a remarkable extent in their essential structures and vary only in such characters as hairiness, wall structure, shape and structure of sacs and spores and other minor details. The accessory spores are some- times found on simple erect threads, from which they are pinched off in regular succession. In other cases the spore- producing threads may be bunched together into cushions, and in still other cases they may be formed in cavities or cases, quite similar to those of many- sac-cases in appearance, though, of course, they do not contain sacs. Moreover, such accessory spores may vary in number and arrangement of cells. They may consist of a single cell or of a definite or indefinite number, which may be built up into a net-shaped complex or into long strings. On the characters of the sac-capsule structure and opening, on sac-spore shape, etc., and on the grouping, struc- ture, etc., of the accessory spores, an elaborate artificial classi- fication of the group has been built up. This system, though artificial, is nevertheless useful as a framework for collecting and describing information about this vast group of plants. The sphere fungi inhabit almost all plant parts though they may be said to be most numerous upon the leaves of their hosts. They are also very abundant on herbaceous stems and may even be found on woody stems, on timbers, roots and fruits. Many needle-cast diseases of cone-bearing plants, as pines, are caused by sphere fungi. Certain root diseases of vines and other plants, the leaf spot disease of strawberry and many other so-called leaf-spot diseases are due to sphere fungi. Apple scabs on leaves and fruits and many other diseases of cultivated plants might be cited as further examples. In fact the great majority of plants harbor one or more of these parasites. They Minnesota Plant Diseases. 139 are not in all cases "dangerous diseases. Moreover, not all of the sphere fungi are parasites : many are saprophytes as are the dung fungi, and many are half saprophytes or wound parasites. (Figs. 35, 60, 153, 183 to 187.) Dead-stick and burnt-wood fungi. These are sphere fungi which are found in great abundance on dead sticks and branches of trees. They are saprophytes or half-saprophytes and the latter do not usually produce their sac-capsules until after the death of the host branch. The sac capsules are very often col- lected together with or without a black mycelial cushion, and they usually break out from beneath the bark, puslr'ng out the latter before them. Often the mycelial cushion is of great size and thus resembles the black-knot in appearance. Such fungi occur in great abundance on oak limbs or oak fence posts and sometimes produce cushions a foot in length. These cushions become black and hard and resemble burnt or charred wood, whence their common name. They are often mistaken for such wood by those unacquainted with their true nature. Birch branches and in fact limbs and stumps, dead or fallen trunks of almost any tree may show such burnt wood fungi. They are very effective agents of decay in wood, though not as conspicuous in their action as the pore and gill fungi of the mushroom group. The highest forms of these burnt wood fungi produce cushions which are club-shaped in appearance and look like charred club fungi. A number of such forms are abundant in our state. In the spring one finds such clubs cov- ered with a white dust of accessory spores, while in the fall the sac-cases are formed and the club is black and warted just as in black-knot. In some of these dead-stick and burnt-wood fungi one finds sac-capsules which open, not by a pore, but by long slits or by star-shaped openings. It is in these forms that wre see the transition to the cup fungi ; for a cup of the cup-fungus group is merely a sac-capsule with a great wide-open top. It has a pore which has become very large so that the capsule when ma- ture has a beaker shape, or may even become saucer-shaped or plate-like in form. Beetle fungi (Labonlbcniinccc). These fungi are parasites on insects and are found in abundance on water beetles. The 140 Minnesota Plant Diseases. plants are very minute and can usually only be clearly seen un- der a compound microscope. On the one hand these fungi show relationships with the sphere fungi, which are undoubted- ly their closest fungus relatives. They form sacs containing spores and these are contained in sac-capsules. The structure of the sac-capsule is not however very similar to those of the sphere fungi. The cases are often long pear-shaped and the sacs are produced over a considerable period of time and do not all mature at once. Moreover, the sac-cases are preceded by a breeding act which is altogether unlike that of any of the sphere fungi but can be best compared with the breeding act in the FIG. 61. — A common cup fungus (Urnula craterium) growing on sticks sunken in the soil and appearing abundantly in the spring. Original. group of algae known as the red sea-weeds. The structure of the mycelial threads is, moreover, very similar to that of the red sea-weeds and the beetle fungi are therefore considered by some botanists to have a common origin with that group of algae. The beetle fungus plants are usually broom-brush- shaped and are found on the legs and wings and outer parts of insects. They are often highly specialized in locality, occurring only on certain joints of the legs and on certain legs of the host. The plants are often of two sexes though some contain both female and male organs. These fungi are undoubtedly numerous in Minnesota though no attempts have as yet been made to collect or determine them. They seldom, however, are very destructive parasites, as is the caterpillar fungus or the Minnesota Plant Diseases. 141 insect molds, and hence are not, as far as is at present known, of great economic importance. (Fig. 30.) Cup fungi (Discomycetes). These comprise one of the larg- est groups of fungi. The range of habit and structure is very great within the group. The cup fungi are very closely related to the sphere fungi, as has al- ready been pointed out. They are all sac fungi and the sacs are always borne in structures com- monly called cups. These cups may be con- sidered as wide-mouthed spore-sac-capsules such as are common in the sphere fungi. In the early stages of many cup-fungi the cup is in fact a sphere entirely closed or with a small pore-like opening. The cups vary greatly in shape and size. In many forms it is very minute and requires a hand lens for its examination. In others it is large, reaching six inches in diame- ter and even exceeding this. Some forms are like long goblets, while others resemble beakers of all shapes. Many, again, are saucer-shaped and some perfectly flat or even more or less con- vex. Some are gelatinous in texture, others cartilaginous or waxy, still others are more or less leathery or simulate burnt wood. Few, if any, have woody cups. They may be furnished with hairs, sometimes with dense masses, and often they have eye-lash-like, hairy spines lining the edge of the cup. The cup is often a very complex organ structurally and in a great ma- jority of cases contains between the sacs sterile threads of very characteristic shapes. The sacs are usually long cylinders and line the inside of the cup with a dense palisade, standing upright in the cup — that is, at right angles to the inside surface. The function of the sterile threads is probably that of assistance in throwing out the spores. The sacs are often provided with little lids at the apex and when the spores are ripe the lid comes FIG. 62. — A single sac and sterile threads from the palisade of sacs of the fungus shown in Fig. 61. The sacs show eight spores. Highly magni- fied. After Seavers. 142 Minnesota Plant Diseases. off and the spores are thrown out in a tiny drop of liquid. Very often comparatively large areas of sacs in a cup throw out their spores simultaneously and then one sees small dust-like clouds arising from the cup. If a little slip of glass be placed over the cup at such times the spores will be found in groups of eight in little drops of liquid on the glass. If cups be placed in a moist chamber and allowed to remain undisturbed for sev- e'ral hours they will often, upon the removal of the moist cham- ber lid, begin to send up the dust cloud of spores. The change of moisture conditions seems to initiate the expulsion of these clouds. A few cup fungi have another device by which the en- tire unopened sacs are thrown out. Accessory spore-forms are known in a great many cup fungi though not nearly so numerous nor in such great variety as those of the black fungi. The great majority of cup fungi live on the ground or on dead wood and are saprophytes, but not a few7 are parasitic and some cause serious diseases of their host plants. As agents in the disinte- gration of plant debris they are important economically, though not nearly so conspicuous in this effect as are the black fungi and the gill- and pore-fungus allies. The two following groups contain most of the common forms of cup fungi. Tar-spot fungi and their allies (Phacidiinece and Hysteriinecc). This group of fungi may be considered as a transitional group between those black fungi whose sac-capsules have large oval or slit-like mouths and the true cup fungi. They produce densely- woven mycelial masses which form crusts with the substrata and upon these burnt-wood-like masses arise the little cups which are similar in texture. The cups are at first closed and simulate the spore-sac-capsules of the black fungi, but the sac-bearing area is soon exposed. The sterile threads between the sacs are usually longer than the sacs and the ends come together above the sacs forming a covering. Accessory spore bodies are not uncommon. These fungi occur on leaves and branches of trees and have the habit of leaf- and dead-stick- inhabiting black fungi. They are, moreover, usually sapro- phytic though tree tar-spots are parasites of economic impor- tance. The tar spots of willow and maple leaves are very abun- dant in Minnesota. The mycelial mass which forms on the leaves in summer and in fall looks like a drop of tar and does Minnesota Plant Diseases. not show any mature cups. The latter are formed on the fallen leaves in the spring. (Fig. 133.) True cup fungi (Pczisincce). The greatest number of cup fungi belong in this group. The great variety of form and size has already been mentioned. Many have long stalks, others are sessile. While the cups vary considerably as to texture, they are usually fleshy or soft and seldom or never woody. More- over, they are very frequently brightly colored, especially in the sac-bearing region. The color is usually contained in the ends FIG. 63. — A cluster of cup fungi, showing cups appearing just above the ground. They are attached to long- stalks, which arise underground from a storage organ. (See Fig. 4.) Original. of the sterile threads between the sacs. The most common colors are reds varying on the one hand from bright scarlet through orange and yellowish reds to lemon-yellows or even lighter shades, and, on the other hand, from scarlet to chestnut, chocolate and violet browns. A few are lilac-tinted and many are \vater-colored or very dilutely brown and tan. There is a great diversity in the surface coverings. Many are perfectly smooth while others are covered with very dense hairs and nu- 144 Minnesota Plant Diseases. merous intermediate conditions exist showing great differences not only in the number of hairs but in the kinds produced. The spores are usu- ally oval in shape and s i n g 1 e-celled, though some are somewhat elongat- ed and many-celled. The explosive appa- ratus for spore or sac ejection has al- ready been noted. It is in the true cup fungi that these de- vices reach the greatest degree of perfection. Acces- sory spore-forms are not at all common. The smaller forms of the true cup fungi abound on dead sticks or dead stems of herbaceous plants or on the ground, especially among mosses, and are often no larger than a pin head. Many grow on dung. The stick - inhabiting forms are not usual- ly brilliant in color, though some are lemon colored. Not a few are parasitic. FIG. 64. — A cup fungus (Plicaria repanda) on the bark of a fallen and decaying tree. Original. Most of the largest forms are saprophytes upon the ground or upon decaying tree trunks or on dung, and are often very brightly colored. Some Minnesota Plant Diseases. cup fungi, and in particular parasitic forms, build storage or- gans, often as large as a small filbert nut, and the cups are produced in clusters upon this storage organ in the follow- ing spring. Wild anemones, cultivated clovers and plant bulbs are often attacked by such storage-organ-forming cup fungi, as are also plants of the blueberry family. In the latter case the storage organ replaces the fruit of the host plant and cases are known where the same fungus lives on two different hosts in its life- time just as do many of the rust fungi; i. e., the fungus produces accessory spores on one host and sac spores on the other. A common disease of certain coniferous trees in the northern part of the state is due to one member of the cup fungus group. Compared with other disease-producing groups, however, the tree cup- fungi are not of very great economic importance, and this is especially noticeable since the cup fungi constitute such a very large group of plants. (Figs. 4, 10, 14, 61 to 65.) Lichen-forming fungi. It has already been stated that lichens are equal-partnership- organisms consisting of an alga and a fungus. In a vast ma- jority of cases, the fungi are members of the cup-fungus group, as is seen by the production of cups. In some lichens, how- ever, black fungi participate and in a very few stalked fungi 10 FIG. 65. — Cup fungus (Helotium citrinum) on decaying wood. Slightly magnified. Original. 146 Minnesota Plant Diseases. are the fungus constituents. The number of lichens in Min- nesota is very great, but a mere passing notice of these can be given here. The constituent fungi of lichens are in reality parasites — in the broader sense — on the algae, but the latter also derive benefit from the partnership. Obvi- ously, therefore, this group of fungi does not produce any diseases of higher plants. The lichens attach themselves to tree-trunks or limbs where they are held in an advantageous position or they grow on the soil or as crust on rocks. In the latter case they act as the pioneers of vegetative life in the invasion of rock surfaces and are usually the first to obtain a foothold. Lichens have invented a peculiar partnership prop- agative body, which is merely a packet of algal cells, wrapped up in a net-work of fungus threads. When such packets come into proper conditions, they commence growth and build up a new lichen plant. In addition, the fungus produces its proper sac-spores and in many cases accessory spores, but when these germinate the resulting mycelium must soon come into contact with the proper algae or the fungus perishes. This is therefore an uncertain means of reproduction of the lichen and the packet device can easily be seen to have advantages over it in the pro- vision for the algal constituent as well as for the fungus. (Fig. 21.) Morels, saddle fungi and their allies (Helvellinece). The saddle fungi are very common plants of our woods. They are all fairly large forms and are fleshly. Their relationship with the cup fungi is easily understood by comparison with the long stalked cups whose sac surface is flattened or turned back. Such are in reality the simplest of the saddle fungi. The stalk in some forms, however, becomes channeled and is often hol- low. The cups in many, moreover, are not only turned back as one might imagine a rubber cup to be turned inside out, but the sac surface often becomes convoluted and lobed or ridged so that the sacs may thus be produced over a greater surface. The saddle fungi are usually whitish in color, or may vary from grey to greyish brown. In the morels the cup, or as it is here termed, a cap, has very greatly increased its spore surface by the formation of ridges which join and form a network enclosing deep depres- Minnesota Plant Diseases. H7 sions. All over the depressions are formed the spore sacs. In some morels the cup does not extend outside of the usually broad stalk, but in others it laps over slightly at the edge. In all morels the cup is drawn out so that seen from the side it is either conical or spherical in appearance. In some forms, the cup is very much convoluted so that it gives a brain-like appear- ance. Closely related to these fungi are certain "earth-tongue" fungi. Many of these are black and burnt-wood-like and look much like club fungi or like the sac-capsule-bearing branch of FIG. 66.— Morel fungi. The ridged caps are to be regarded as everted cups, whose sur- face has become ridged and hollowed to afford large area for spore formation. Original. the caterpillar fungus. The upper part of the club, however, is really a pulled-out cup and hence is like a morel which has lost its ridges and become smooth. They grow commonly in the 148 Minnesota Plant Diseases. ground among grasses and are not at all conspicuous or very large. Another relative of the morels is the spathula fungus which is so common on the mossy floors of our northern woods. Here the cup is drawn out and flattened like a spathula and is yellowish in color. Very common on the ground and amongst moss in summer and fall, can be found a peculiar little gelatinous fungus of a light to dark green color. The fungus has a stalk and a bent back cup similar to the saddle fungi, to which it is closely related, but its cup is neither wrinkled nor ridged. (Figs. 10, 66, 67.) FIG. 67. — Saddle fungi (Helvella lacunosa). The saddle is an everted cup with the edges turned back. Original. True truffles (Tuberinece). At first sight the truffles would not be recognized as relatives of the cup fungi, but such they are nevertheless. The cup remains closed, however, and the plants are found underground, never coming to the surface as do many puff balls to discharge their spores. The spores, therefore, are only distributed after the decay of the cup by being washed away in rainwater or are scattered by the scratch- ing or burrowing of animals. They are sought after by animals as food and they are also much prized for food by man. Euro- pean truffles furnish the most highly prized mushrooms known. The closed cup of the truffles has a sac-bearing area, which is usually greatly convoluted, so that the interior of the truffle Minnesota Plant Diseases. 149 consists of a great labyrinth of pockets and canals which are lined with the spore sacs. The truffles which have been found up to the present time in Minnesota are not large, the largest reaching the size of a small walnut. They are brownish or blackish in color and regularly or ir- regularly spherical in shape. Two forms have been discovered and un- doubtedly more ex- ist. Many forms mature their under- ground cups late in autumn so that they can be found in the ground in early spring. Others ma- ture in the summer. (Figs. 10, 68, 69.) Imperfect fungi and leaf spots (Fungi imperfecti). As has already been ex- plained, the so- called imperfect fungi include an enormous number of plants which are as yet incompletely known. Most of them are undoubt- edly accessory spore-forms of the black fungi or of the cup fungi. One can imagine that a fungus spore-form of this kind might be- come separated from its connection in the life-story of a black fungus, in that the mycelium arising from such a spore would give rise only to the accessory spore-form. On ac- FIG. 68.— Truffles (Tuber lyoni). The truffle may be re- garded as an unopened cup fungus with its internal spore-bearing surface greatly convoluted. That which corresponds to the opening of the cup fungus is seen as a furrow in 2 and in the sections 1 as a broad whitish streak. 1 shows the truffle cut open; the chambers in which the spore-sacs are formed can be clearly seen. Photograph by F. K. Butters. Minnesota Plant Diseases. count of the infrequency of the occurrence of proper condi- tions, it might forget how to form sac-spores and would thus become independent of the sac-spore form. Both the produc- tion of different kinds of spores by one fungus plant and the production of spores on different hosts in one life-cycle would tend to furnish fungi where such a separation might occur. In addition to those forms where this actual separation and inde- pendence occurs there is a considerable assembly of spores, where the connection of apparently inde- pendent forms with sac-spore stages is known, and in such cases the term "imper- fect" is in a sense a misnomer. In a vast number of forms, the connection is indicated to a certain degree by the connections of an- alogous forms. For instance, the accessory spore forms of the powdery mildew is of a definite type known as an Oidium, and when one meets with such isolated spore forms, if they occur in the usual habitats of mildews, one may refer them to the powdery mil- dew group. Indeed it may be that all so-called imperfect fungi are actually traceable in their connections with sac-spore forms, but many have, as yet, frustrated all attempts to prove such connections. We may sum up these forms in this re- spect into three groups : first, those isolated forms whose con- nection with sac-spore forms is known; second, those isolated forms whose sac-spore connection is not known, but suspected from analogy with known forms; third, those isolated forms whose sac-spore connections are not even suspected or have become actually independent. FiC. 69.— Truitie. 1. Fruiting body cut open; surface furrow which corresponds to the opening of a cup fungus is seen below and the convoluted sur- faces of the cup interior above. 2. A portion of the interior showing the sacs, each with four spores (highly magnified). 3. A single sac show- ing four spiny spores. Very highly magnified. After F. K. Butters. Minnesota Plant Diseases. As a matter of convenience and for the collection of statistics and data, the imperfect fungi are classified in an artificial sys- tem according to the aggregation of spore-bearing threads, and each of these again into groups according to the number of cells in a spore and the arrangement of these cells. The three primary groups are: first, the loose-thread forms, i. e., those in which the spore - bearing threads are borne loosely in mold- like fashion; sec- ond, the cushion- forms, those in which the spore- bearing threads are joined to- pic. 70.— Two types of imperfect fungi. 1. An elongated cushion type where the spore-bearing threads are crowd- ed together to form a cushion. The free, many-celled spores are seen above. 2. A capsular type. The spore- dust is seen above escaping from an opening in the top. Both highly magnified. A third type might be illustrated in Fig. 1. After Tulasne. gether to form cu slri o n s; and third, the capsu- lar forms, those in w h i c h the spore - bearing threads are borne in cases, often similar in appearance to the sac-capsules of the black fungi. Un- der each of these are sub-groups based on the color and cell structure of the spores. The imperfect fungi are of very great importance econom- ically on account of the great number of serious diseases pro- duced by them. These diseases often take the form of spots on leaves of the host plants and are then known as "leaf spots." Hence the fungi are often known as leaf-spot fungi. These spots may be whitish or brownish and are sometimes ringed with a whitened or reddened area. The spot is often character- istic for certain fungi. In some cases they are black, whence the disease is known as coal-spot disease or anthracnose. Sometimes the infected spot region falls out, leaving small holes which give rise to the common "shot-hole" disease of cer- tain cultivated plants. The spots are not, however, in all cases 152 Minnesota Plant Diseases. well defined but may extend out indefinitely over the attacked organ. Many fruit rots are caused by these fungi, as the brown rot of plums and ripe rot of apples. Sometimes the influence of the fungus causes the fall of the leaves with great injury to the plants, as on currant bushes. Some imperfect fungi, more- over, attack stem portions, particularly the young stems, and then may do considerable damage. Many are, on the other hand, saprophytes and as such, just as the majority of black fungi, are important agents in the disintegration of plant debris. (Figs. 35, 70, 156 to 159, 164, 165.) Chapter XI. Fungi. Kinds of Fungi. Basidium-bearing Fungi* The stalked or basidium-bearing fungi (Basidiomycetes). This is the third of the three great groups of fungi. The members of this group do not, as the sac fungi, bear their spores in sacs, but form them upon more or less definite stalks, which occur with some degree of regularity upon special por- tions, usually the ends, of the fungus threads. From these stalks the spores are pinched off just as are many accessory spores in sac fungi. They are not formed internally, as the spores are in sacs, but are externally formed in the pinching- off process. The stalks usually occur in fours at the end of the thread though they may be fewer or greater in number and may arise laterally on the stalk-bearing threads. The cell or cells of the thread which bear the stalks are known as the basidium. In the lower group of the stalked fungi, the basidi- um is composed of a number of cells each of which bears a stalk with its spore as in rusts and smuts, "Jews' ear/' trem- bling and weeping fungi. In the higher forms, comprising the other groups, all of the stalks arise from a single undivided cell. The basidium may arise directly from a spore (winter spore) as in the rusts and smuts. In these forms, of course, they are often found singly, but when the winter spores are formed in crust-forming clusters they are produced in a more or less dense mass. In all other stalked fungi the basidia are borne on or in some fruiting body or on the surface of mold- like growths. The former is by far the more common form, as in the gelatinous fungi, in the mushrooms and all of their allies and the great alliance of puff balls, birds'-nest and car- rion fungi. When borne at the surface of a fruiting body the basidia usually stand closely together side by side and perpen- dicular to the surface of the fruiting body, with occasional sterile threads between them, thus constituting a palisade, cov- 154 Minnesota Plant Diseases. ering the entire spore-bearing surface. Such palisades are common in all of the mushroom allies, in most gelatinous fungi, "Jews' ears/' etc. In many of the closed fruiting bodies, e. g., puff balls and birds'-nests, internal chambers, which are formed in the early stages of growth, are lined with such pal- isades. The fruiting body may assume many shapes, which apparently tend toward the increase in spore-bearing area or have to do with advantages of distribution. The variety of forms is enormous — ranging from such sim- ple types as the club fungi and smooth shelves to the tooth, pore and gill fungi, and from puff balls to carrion fungi. The teeth, pores and gills are the basidium-bearing regions. In the puff-ball allies, the birds' nest and carrion fungi, the spore-bearing region is in a closed fruiting body which either opens only by decay or at maturity by a special pore or other device. Inside of these closed bodies the basidia may occur in palisades lining the surfaces of chambers, or they may occur on wefted threads in no regular arrangement. The details of the fruiting bodies will be given under the various groups. In a comparatively few forms accessory spore-forms are found but they are not nearly so common in this series oi fungi as they are in the sac fungi. The question of the occurrence of a breeding process is still an open one. A fusion of elements in the young basid- ium or in the winter spore of rusts is interpreted by many as a breeding act, and recent investigation has shown that in the rust winter-spore the fusion is the culmination of a breeding act which begins in the cluster-cup stage. The stalked fungi do not seem to show any striking similarities to either the algal fungi or to the sac fungi, so that in the light of present knowledge only an isolated position can be assigned to them. Various theories have, however, been proposed uniting this group with each of the other great fungus groups. The latest investigations indicate a relationship with the red sea-weeds. Perhaps the majority of the stalked fungi are earth-inhabiting or wood-inhabiting saprophytes. Many, however, as the rusts and smuts, are highly specialized and destructive parasites, while not a few, as pore and other shelf-fungi, are half-sa'pro- phytes. The timber and timber-tree diseases are largely mem- bers of this group and the rusts and smuts are without doubt Minnesota Plant Diseases. 155 the most destructive disease-causing alliances of the whole group of the fungi. As food producing fungi, the stalked fun- gus group is very important since all of the true mushrooms, the edible pore fungi, club and tooth fungi, as well as the great variety of puff balls are found in this group. The basidium-bearing fungi comprise the following twelve groups. Of these the last eleven possess true basidia, i. e., with a definite number of stalks and spores which are usually definitely arranged as at the summit or on the sides. In the smuts, however, the basidium, if so it may be called, bears a great number of spores which are budded off in yeast fashion from the side of the basidium cells. In other words the basid- ium of the smuts has not attained to the definiteness of the other basidium-bearing fungi and the smuts are often classed as a group outside of these. (For figures, see following groups.) Smuts (Ustilagine&). Though not a very large group of fungi the smuts are very important from the economic stand- point because they contain many disease-producing forms. The smuts possess the simplest form of basidium found in the stalked fungi. They are all parasitic and many of them are half-parasitic in habit, since they are able to live in certain stages for an indefinite period in culture media. They can, how- e/ ever, complete their life-story only as para- sites on certain plants. The basidium arises directly from a resting-spore which is commonly known as the smut spore, , producing the so-called smut of grain and ^ of other plants. This smut or resting spore is usually black, dark-brown or dark- green in color and has a thick outer coat, which, under favorable conditions of moist- ure, breaks open and allows the inner wall to be shoved out in the form of a thread. This thread grows out to six or more times the length of the spore. It then becomes divided by cross-walls into three or four cells, each of which buds off an indefinite -el FIG. 71. — S m u t spores, germinating; cl the smut spore, t the thread growing from it, and c the spore produced by the tube. 1. Wheat smut — the thread is di- vided up by cross walls into cells, each of which buds off spores from its side. 2. Stinking smut of wheat —the thread from the spore is undivided and produces a crown of thread-like spores at the top. Highly magnified. After Brefeld. 156 Minnesota Plant Diseases. number of spores from its side or end. The thread thus con- stitutes a basidium. In one of the smut groups the basidium is not divided but consists of a single cell from the end of which the spores are produced. These spores may be known as the basidium-spores. They germinate immediately in warm, moist conditions, by sending a fine thread, which seeks the host plant and penetrates into the tissues, thus beginning the parasitic life. If the basidium-spores are placed in a nourishing solution they bud in yeast fashion and will so continue to do for an indefinite period as long as the nutrient material is present. It is still able to infect a host plant under proper conditions. The parasitic life usually begins in some young undeveloped part of the host, e. g., the corn smut infects only young leaves or young kernels of the corn. Here the parasitic mycelium grows and builds itself up at the expense of the host plant. In the oat smut the parasite gains entrance to the oat plant only in the seedling stage of the latter. Now this penetration is accom- plished in a peculiar way. In an oat field with smut the sound grains of the oat become dusted with the spores of the smut and thus at the seeding time in the spring the seed grains may have spores on their surface. Now the conditions favorable to the germination of the oats are also favorable to the germina- tion of the smut spores and when the seedling oat appears above ground there are also near by germinating basidium- spores of the smut. The threads of these spores therefore easily reach the young seedling and rapidly penetrate to the growing-point of the stem, although this growing-point is hid- den by the first leaves of the seedling. When the seedling continues to grow, the parasite also grows, always remaining in the growing point and forming patches of mycelium in the growing points of all of the branches. The oat plants thus affected do not appear very different from uninfected plants until the grains mature. When the grains are still very young the parasite invades all of them and here builds up a dense mass of mycelium at the expense of the rich food materials which the oat plant furnishes to the grains. At the time when the oat grains are ripe the fungus threads divide up into numerous cells and from each cell is formed a spore, whose wall is at first gelatinous but later is black, Minnesota Plant Diseases. thick and hard. These spores are produced in enormous numbers re- placing all of the grains and are then seen as a smutty pow- der which is familiar to every farmer who raises oats. These smut-spores are now in an advantageous position and are scat- tered by the wind and carried to sound grains and may, as described above, again cause i n f e c t i o n of the oat in the seedling stage in the following spring. This life-story explains the success of the hot water method in preventing oat smut, for if the smut spores, clinging to the grains are killed by steeping in hot water, which will not injure the grain, then the chances of infection of the seedling plants from these treated grains are greatly re- duced or entirely de- stroyed. 157 FIG. 72.— Loose smut of wheat. (Ustilago tritici.) The loose powder of spores has been par- tially shaken out; the grains of the wheat are all smutted. Original. „ . , 158 Minnesota Plant Diseases* Smuts very often possess the power of stimulating their host plants to abnormal growth. Thus in the corn smut, the attacked part of the corn plant swells up into a tubercle many times larger than the original plant part. The advantage of this to the para- site is obvious, for it increases many-fold the area of the feeding ground as well as the spore-producing area. Such tubercles in corn smut are found on leaves, young stems and on kernels and even in the tassels. In some smuts the stimulation is exerted on the rudiments of organs which are not normally produced in certain flowers causing the rudiments to develop into mature organs. Such is the case in certain pistillate flowers of the Pink family where the smut stimulates the rudiments of the stamens to mature de- velopment. The smuts are parasites, chiefly of the flowering plants and particularly of the grass family. One smut, however, inhabits the capsule of the peat moss plant. The choice of organs for the establishment of the parasitic mycelium varies with different smuts. A very large number live in the grains and seeds of plants, where they get both advantage of position for spore dis- tribution as well as an abundant supply of food material. Sometimes a whole inflorescence is destroyed. The floral parts are also attacked by smuts, e. g., certain smuts fruit only in the anthers of species of the carnation family, forming their spores in place of the pollen so that when the flower opens a violet smut dust is discharged from the anthers instead of the pollen dust. Leaves of the host plant are commonly attacked and are often swollen on account of the stimulation of the parasite. Stem parts may be attacked and one smut is known in Minne- sota to produce its spores in the roots of certain rush-like plants. Almost every cereal plant is subject to the attack of one or more smuts and many of the wild grasses are likewise invaded. The common corn, oat and wheat smuts are best known. Many garden plants such as onion and violet are subject to smut attacks and this is also true of many members of the Pink family, where the smut often lives in the anthers of the flowers. The dock family of flowering plants is also peculiarly subject to smut attacks and this is also true of the pink family. Other flowering plants are attacked but not so commonly as the above mentioned groups. (Figs. 27, 71, 72, 146 to 151.) Minnesota Plant Diseases. 159 Rusts (Uredineai), The rust fungi constitute a larger group of plants than the smuts and exhibit more variety of structure and habit. They may be considered as relatives of the smuts in that the winter spores of the latter may be compared with FIG. 73. — Spores of rust fungi. l.-A cluster of winter spores of wheat rust (Puccinia graminis) on wheat plant. 2. A winter spore germinating to a thread of four cells (promycelium — basidium), each of which bears a small spore (sporidium) on a stalk. The winter spore germinates in the spring while still in the straw or on the ground. The sporidia are blown by the wind to another plant and there germinate as seen in 3 and 4. 4. Shows the germination of a sporidium on a barberry leaf; here infection will soon take place. 5. A germinating summer spore of wheat rust, showing germ tubes which on a wheat plant can cause infection (as shown in Fig. 29). 6. A rare grass rust spore (amphispore of Puccinia vexans) germinating; it germinates as a summer spore, but has a thick coat and rests over winter as a winter spore. All highly magnified. 1-5, after Ward; 6, after Carleton. (See also Fig. 74.) the smut spores. The rusts, however, exhibit a great number of accessory spore forms. They are all parasites and are of great economic importance on account of the large number of dis- ease-causing forms. The life-story of a rust plant is often very 160 Minnesota Plant Diseases. complex. We will start with the winter spores. These spores are in a great majority of cases resting spores and, as in the case of the smut spore, are provided with very thick outer coats. These winter spores may be formed singly on stalks on the ends of short threads, where they are usually produced in dense clus- ters, just under the host plant epidermis and are liberated as a brownish or blackish powder by the rupture of this epidermis. This procedure is common in grass-inhabiting rusts, in the rusts of sunflower and mints. In the rusts of willow and poplar the winter spores occur in a crust-forming mass, just under the host cuticle, and are never shed but germinate in place. This is also the case with the common golden-rod rust. The winter spores in the cedar apple disease of cedars are borne in various- ly-shaped masses of gelatine which expand much on absorption of water and in which the winter spores germinate producing the basidium-spores at the surface of the gelatine. Some, again, as in the milkweed rust, produce long, thread-like bodies composed entirely of winter spores. In the rust of the cow- berry the winter spores remain in the cells of the host epidermis and germinate there. Whatever the location or method of dis- tribution of the winter spore may be, it always germinates in essentially the same way. There are usually thin places in the outer walls and through one of these the inner spore wall is pro- truded in the form of a thread. This thread increases in length as does that of the smut spores and also becomes divided, usual- ly by three walls. Each of the resulting four cells sends out a stalk on the end of which is formed a spore. The thread bear- ing the four stalks and spores is the basidium and is noticeably more definite than the smut basidium in the production of but four spores, which are formed on stalks. The basidium-spores are scattered by the wind, and germinate as soon as placed un- der favorable conditions; they are capable of infecting host plants just as is the basidium-spore of the smut. The winter- spore is not the only spore-form produced by rusts. In the spring the mycelium, which develops from the basidium-spore, produces what is known as cluster cups. These are tiny cups scarcely as large as a pin head, usually yellowish or whitish in color and found in clusters. They are most commonly found on conspicuous yellow spots in the host plants caused by the Minnesota Plant Diseases. 161 mycelium of the fungus. The cups are at first closed and then resemble small spheres ; the walls later open at the summit, roll back and expose the spores as an orange-yellow dust. The spores are formed in chains which arise in a palisade from the floor of the cup and are formed continuously for some time, f FIG. 74. — More spores of rust fungi. 1. A pycnidium (from wheat rust on barberry), a capsular spore-bearing fruiting body showing dust of spores at r. 2. Spores and spore-bearing threads from 1 greatly enlarged. 3. Same spores germinating. These spores are probably the relics of male reproductive cells which have fallen into disuse. They appear to be functionless since they do not usually germinate and have never been known to cause infection. 4. A cluster-cup of an Anemone rust; s spores, formed in chains; p, threads forming the cup of the cluster-cup. All highly magni- fied. After Tavel. those at the summit being the first to mature. These cluster- cup spores are ball-shaped or have flattened sides and their outer wall is frequently provided with small warty roughnesses. The cluster-cup spores are blown about by the wind and are capable of immediate germination. When germinating they send out a germ thread which causes infection. Accompanying 1 62 Minnesota Plant Diseases. the cluster-cup stage or rather just preceding it one very often finds another accessory spore-form in which small spore-cases of pear-shaped structure are produced, sunken into the oppo- site— usually upper — side of the leaf from that on which the cluster cup occurs. Inside of these pear-shaped cases the spores are produced on long threads from which they are pinched off just as in very similar structures found in many of the acces- sory spore-forms of the sac fungi. These spores are often ac- companied by the production of sugary, sweet fluids which are probably attractive to insects and thus aid in spore distribution. The exact use of these spores is not yet known for they have not been proven to be able to cause infection of a host plant though they will germinate under certain conditions. They have been supposed to be unused male sexual elements and re- cent research points to a confirmation of such a supposition. Sometimes this pycnidium spore accompanies other spore- forms, e. g., the summer or even the winter spores. The cluster- cups are produced almost universally in spring so they are the first rust spores (excepting the pycnidia and basidium-spores) which one finds after the resumption of growth by flower- ing plants, after the winter has passed. In early summer or even late spring and from this time throughout the summer season and far into the au- tumn are found what are known as the summer spores or red rust spores. These are like the cluster-cup spores FIG. 75.— Cluster-cups of ash-leaf rust fun- „ • cnrnp rpcnpr-f c • fk^r -ar^ r^r gus, on ash twig. The cups are long m some respects , they are or- cyliiidrical. Highly magnified. Micro- anp-p-reH or VpHow in rolnr photograph by E. W. D. Holway. and are often provided with external warts or spines. They are, however, not formed in closed cup cases and are not formed in chains. They arise singly on short stalks in dense clusters from which they are shed as a red-rust powder. They may be formed continuously for long periods from the same cluster, and are capable of im- mediate germination under favorable conditions. They ger- minate by sending out a fine thread in a similar manner to that Minnesota Plant Diseases. 163 of the cluster-cup spore and this thread may cause infection. They are scattered by the wind and are the chief cause for the rapid spread of rusts through the fields of wheat and other cereals. Towards the end of the summer, often in the same cluster with the summer spores, the winter spores commence to develop and continue to form until late in autumn. In many cases, however, the winter spores are formed in separate clus- ters. The variety of habit of these winter spores has already been described. They are in general resting-spores and germi- nate in the following spring, thus again commencing' the life- story. It may be well to summarize at this point the order of succession of these spore forms. First at the germination of the winter spore on the ground or under moist conditions any- where, the basidium spores are produced. Soon after on a suit- able host the pycnidia appear, followed closely or accompanied by the cluster-cup spore. Next in late spring commences the formation of the summer spores which may continue to form until late in fall. From mid-summer on the winter spores may be produced until snow flies in late autumn. There are thus five kinds of spores of which the winter spore corresponds to the smut FlG 76._cluster.cup spores from rust fun. spore of the smuts. In addi- g?.s of Fig. 75 Highly magnified. Microphotograph by E. W. D. Holway. tion to these five forms a sixth is known but is of rare occurrence and seems to be very similar to the summer spores in some respects. Not in all rust fungus life-stories, however, do all of these spore-forms occur. One or more may be missing so that nu- merous combinations are conceivable and actually occur. For instance, a rust fungus may possess no cluster-cup stage or no summer-spore stage, or both may be missing. In fact, some have apparently retained only the winter spore form, which, of course, always bears the basidium spores later. In addition to this variety of spore-forms, rusts have fur- ther complicated their life-stories by selecting different hosts upon which to form their various spores. For instance, one of 164 Minnesota Plant Diseases. the common rusts of wheat forms its summer and winter spores on the wheat plant, but the pycnidium and cluster-cup spores are formed on the common buckthorn. The fungus which forms its winter spores on the cedar ap- ples of the red cedar produces its cluster-cups on apples and pears, having no summer spores in its life-history, but it pro- duces its cluster-cups throughout the summer. The life-story of such a rust fungus which possesses five kinds of spores, four of which are produced from a parasitic mycelium and two of the latter on one host and the other two on another host, offers an exceedingly complex history. It may be remarked in passing that to combat such accomplished parasites requires an intimate knowledge of their histories. The question of a breeding-act in the rust life-history is still, perhaps, an open one. A fusion of two elements in the young winter spore has been interpreted as such an act by some botanists. Recently, the beginning of the association of these sexual elements has been discovered just preceding the forma- tion of the cluster-cup. The rusts are all parasites — true parasites, unable to live ex- cept in the tissues of their hosts. The mycelium grows inside of the tissues and the spores are in almost all cases borne at the surface of the plant, whence they can best be shed ; but some, buried in the tissues, depend on the decay of the host plant for their release. The rusts vary greatly, also, in their location on the host plants. Most commonly they are found upon the leaves but in many forms the stem is also attacked and even the under- ground portions may be invaded. Floral parts are seldom directly attacked. The rusts also possess in some cases the power of stimulation of the host to extraordinary effort, thus increasing the available food supply for the fungus parasite. The cedar apples of the red cedar are merely enlarged twigs of the cedar tree in which a rust mycelium is at work. Some rusts on pines produce great swellings on the stem and still other cases might be cited of the deforming and stimulating effect upon the host by rust parasites. Witches'-brooms are very often of rust-fungus origin. Such is the common birds'- Minnesota Plant Diseases. 1 65 nest broom of the red cedar and the great bush- like brooms of the bal- sam fir. These have al- ready been described as stimulated portions of the host plant which, with the fungus parasite, live in partnership at the expense of the neighbor- ing parts of the host. Besides this deforming power of many rusts these parasites are injuri- ous in the stealing of nourishment which they accomplish at the ex- pense of the host and in the wrounding of plant parts. The host, as a re- sult, becomes impover- ished and may finally en- tirely succumb. Thus wheat rust annually robs farmers of enormous sums of money by im- poverishing wheat plants. Practically all classes and groups of flowering plants are attacked by rusts as are also certain fern plants. The lower plants as mossworts and algae seem to be free from these parasites. The favorite hosts of the rust fungi seem to be the grasses, for on these plants are found an enor- FIG. 77. — Spores of a grass rust fungus (Puc- cinia vexans) ; above, winter spores; in the middle, summer spores; below, amphispores. (Summer-spore-like in germination, but rest- ing over winter.) Highly magnified. Micro- photograph by E. W. D. Holwav. 1 66 Minnesota Plant Diseases. mous number of rust fungi, constituting many of the most im- portant diseases of cultivated crops. Wheat rusts have been mentioned. The cluster-cups of the cedar apple fungus are often destructive to pear and apple trees. Of great importance are also the asparagus rust and mallow rust and the numerous rusts of beans and clover. The great rust disease of the coffee plant, though not, of course, directly affecting Minnesota plants, has been of enormous importance in its devastation of the coffee crops of India and Ceylon. In addition to these might be mentioned a host of parasitic rusts which yearly levy a tax on field and garden crops, on wild plants and greenhouse plants — in fact, they are almost universal in their distri- bution. (Figs. 2, n, 23, 26, 29, 73 to 77, 136 to 145, 160 to 162, 181, 182, 199 to 201, 205 to 209.) Jews' ear fungi (Auriculariinece). This group of fungi derives its name from the name of a common member of the group — a very widely distributed fungus. The nearest relatives of the Jews' ear fungi are the rusts, though at first sight this fact is not apparent. These fungi are almost all saprophytic, growing chiefly on wrood, but one spe- cies is apparently a parasite upon mosses. Unlike the rusts, winter spores are not produced, but a basidium very similar to that of many rusts is formed directly on threads of the fruiting body. The basidia are long cylindrical bodies of four cells, and they stand side by side in a dense palisade, form- ing one surface of the fruiting body. The latter is variously shaped : club-, spoon-, shelf-, or ear-like, and is found at the surface of the log or whatever substratum may furnish the nutrient material. The vegetative mycelium is found in the log just as is the mycelium of the pore or shelf fungus in wood- inhabiting saprophytes. The fruiting body of the Jews' ear FIG. 78. — Various basidia and spores of the lower basid- ium-bearing fungi. 1. Jew's-ear fungus; a, a basidium; b stalk with basidiospore. 2. Trembling fungus; the basidium is longitudinally divided. 3. Weeping fungus; has an undivided and forked basid- ium. Highly magnified. After Brefeld. Minnesota Plant Diseases. 167 fungi is in almost all cases of a gelatinous consistency, especial- ly in the interior, and this is due to the gelatinization of the outer portion of the fungus threads, which compose it. The threads, therefore, appear as a very loose network in a great mass of gelatine. Near the surface of the fruiting body the thread walls do not gelatinize but, by the dense network there produced, form a tough covering. The basidia usually cover a special area as they do in the common Jews' ear fungus. In the young basidium a fusion of elements similar to that in the young winter spore of rusts occurs, and has also been inter- preted as a breeding act. When the fruiting body is dried, it usually becomes hard and horn-like and shrinks very greatly in size. From each of the four cells of the basidium a stalk is sent up to the surface of the palisade area and there pinches off a single spore just as do the basidia of the rust fungi. The Jews' FIG. 79. — Jew's-ear fungus fruiting bodies on a dead branch of balsam fir. Original. ear fungi have also accessory spore-forms, but not in such abundance nor with such variety as they are found in the rusts. The common Jews' ear fungus, which is found almost all over the world, has been collected only in the northern part of our state, where it occurs in great abundance on dead logs of bal- sam fir, white cedar and other trees. (Figs. 78, 79.) Trembling fungi (Trcmcllinece). These fungi include forms which have a great superficial resemblance to the Jews' ear fungi and derive their common name from the gelatinous con- sistency which allows them to tremble, as it were, at the slightest agitation. They are all saprophytic, usually on de- caying wood and logs. The fruiting body assumes in different i68 Minnesota Plant Diseases. plants a great variety of forms — usually from club-shaped or cylindrical to ear-shaped and shelf-like. Many of them are very irregular in form and much convoluted, forming brain-like masses, while still others have a surface furnished with teeth in an exactly similar fashion to those of the true tooth-fungi. They are all, however, gelatinous and this character is due to the same structure of the threads as was described for the FIG. 80. — A trembling fungus (Tremella sp.), on the end of a log. The portion of the fruiting body near the top has partially decayed and deliquesced. (In the center of the cluster are two white caps of a gill fungus.) Original. Jews' ear fungus. From the latter and from the true palisade fungi the trembling fungi differ in their basidium. This is formed directly from the ends of threads as in the Jews' ear, but the walls, which divide up the basidium into cells are longi- tudinal or oblique and the basidium itself is spherical or pear- shaped, while in the former groups the basidium was cylindrical Minnesota Plant Diseases. 169 and bore cross walls. Externally, therefore, the Jews' ear and trembling fungi and also the following group may be very simi- lar and indistinguishable to the naked eye, but the microscope shows a difference in the structure of the basidium. Similar accessory spore-forms are also produced in the trembling fungi and a very considerable variety of such forms is found. The trembling fungi are very common in our woods, growing on dead sticks and logs, especially after heavy rains. After shed- ding their spores they usually liquify under the action of bac- teria and other organisms, for they furnish good media for these plants. When dried the trembling fungi become hard and horn-like, resuming their gelatinous nature when again placed in water. One of our common forms resembles a brownish, irregular or shelf-like mass of gelatine and is commonly known as witches'-butter. The brain-like forms are also very common, often producing masses weighing five pounds. Toothed forms have been found in several places in the state but are seldom abundant. These toothed forms are not unlike the true toothed fungi in appearance but are always more or less gelatin- ous. Economically this group of fungi is not important, though they may aid in timber rotting to a slight extent and a few forms have been pronounced edible. One very common form is tough and leathery and resembles greatly a much- branched club fungus. (Figs. 78, 80.) Weeping fungi (Dacryoui \ceti nccc). These fungi include an- other group of gelatinous fungi similar in apparent characters to the two previous groups. There is again a variety of shapes produced, but our commoner forms are irregularly club-shaped or brain-like. The basidia are again arranged in palisade-like areas at the surface of the fruiting bodies, but these basidia are single-celled, having no walls dividing them into several cells. The basidia are fork-like in form and each of the two tines of the fork bears at that end which comes to the surface of the gelatine a single spore. Accessory spores are also produced. The most common Minnesota form is one, which is abundant on fallen logs and stumps of larch and other soft woods. It is at first bright orange, but soon after the shedding of the spores the fruiting body liquifies, whence its common name of weeping fungus. Chapter XII. Fungi. Kinds of Fungi* Bastdium-bearing Fungi. The palisade fungi (Hymenomycetes). All of the remaining groups of the basidium-bearing fungi have one common charac- ter, viz. : the structure of the basidium. Like that of the weep- ing fungus the basidium is a single cell, not, however, fork-like. It usually bears its spores at the summit. The spores are com- monly four in number. The palisade fungi possess such single-celled basidia. The basidia are borne on fruiting bodies and are always arranged in a palisade which at least at maturity is exposed to the open air. This palisade of basidia lines special surfaces and only in a few cases does it cover the entire fruiting body. The fruiting body therefore exhibits a great variety of forms each of which is a special solution of the problem of furnishing large spore- bearing surfaces and exposing them to the wind for advantageous distri- bution. The simplest forms are pros- trate and mold-like. From this to the highly-organized pore and gill fungi we find an enormous variety of fruiting bodies. Comparatively few accessory spore-forms are known though some exist. The palisade fungi constitute an enormous group of fungi and since the basidia are sim- ilar in all, the shape of the fruiting body is utilized in arranging the forms into groups. The group may be divided into the fol- lowing seven sub-groups : Gall-producing fungi (Exobasidiinece). These fungi are all parasites, chiefly of the blueberry and heath families. The my- FIG. 81.— Basidia and basidio- spores of all of the higher stalked or basidium-bearing fungi. 1. The usual type. 2. The basidium of a stalked puff- ball. Highly magnified. 1. After Brefeld; 2. After Schroe- ter. Minnesota Plant Diseases. 171 celium stimulates the leaves or stem to excessive growth, and gall-like swellings, often reddish in color, are thus produced. On the surfaces of these galls the palisades of basidia are pro- duced, and the basidium-spores appear to the naked eye as a fine white powder. Four spores are produced on each basid- ium. These spores germinate by forming a thread, which is again capable of causing infection. The galls so produced are fungus-galls and must be distinguished from- the insect galls of plants which are much more common in occurrence. The most common Minnesota member of this group is one which forms galls on Labrador tea in the northern part of the state. The gall on blueberry and cranberry undoubtedly also occurs but it is not very abundant and good specimens have not been collected. (Figs. 37, 81.) Mold palisade fungi (Hypochnacece). These comprise the simplest of all palisade fungi since no true fruiting body is formed but merely a dense mold-like mass on rotting logs or decaying wood. On the surface of this mold-like mass are the basidia arranged irregularly and only suggesting the true pal- isade of the higher groups of this alliance. Smooth shelf fungi (Thelcphoracece). In this group of fungi the palisade is usually the under surface of a shelf-like fruiting body. In some forms, however, the fruiting body is prostrate and closely grown to the log or substratum on which it grows and no part of it shelves out. In this case the whole upper sur- face is covered with a palisade. Such prostrate forms often ap- pear as thin, grey-brown or whitish crusts on the bark of dead twigs and trunks of trees. Whatever the form of the fruiting body the palisade surface is always smooth and in this respect it differs from the pore and gill fungi. The palisade surface, moreover, is not entirely composed of basidia but may contain certain sterile cells of peculiar structure, known as cystidia. They are usually long, sharply-pointed cells which project from the surface very considerably and are frequently coat- ed with certain salts which give to them additional rigidity. Their function is probably protection. When occurring in great numbers they give to the palisade surface a velvety ap- pearance as seen by the naked eye or under a low-power hand lens. The smooth shelves are very common Minnesota fungi 172 Minnesota Plant Diseases, and not a few timber diseases can be traced to this group. Most forms are, however, saprophytes. . The common smothering fungus which is found at the base of young shrubs and trees is a smooth-shelf fungus. (Figs. 81, 82, 117, 118.) Club fungi (Clavariacccc). As the common name implies, these fungi have club-shaped fruiting bodies. The club in some forms is single and thus simple. In other forms it may be branched and the most common of our club fungi are very abundantly branched thus forming dense tufts. The palisade surface is usually confined to the upper part of the club which is in general smooth, so that one may consider these club FIG. 82. — A smothering fungus (Thclephora laciniata), growing on the ground. The fruiting body has narrow shelf-like divisions. Original. fungi as but modifications of a similar scheme of fruiting body to that of the smooth shelves but of a special kind. The basidia are of the usual type and the spores vary from white to yellow. The clubs are sometimes hollow and very brittle, in other cases they are solid and fleshy. All of our club fungi are saprophytes inhabiting decaying wood or ground where wood has been scat- tered. They vary in size from tiny thread-like cylindrical clubs, on the one hand to large single clubs measuring six inches in length and one inch in thickness and on the other hand to clus- ters of branched clubs six to eight inches in diameter and even larger. One little club, not commonly, but occasionally, found in Minnesota, has a swollen and somewhat convoluted club top Minnesota Plant Diseases. 174 Minnesota Plant Diseases. which is internally more or less gelatinous and of which the en- tire surface is covered with the palisade of basidia. A large number of the club fungi are edible and furnish many common and abundant forms. (Figs. 10, 81, 83.) FIG. 84.— The coral fungus— a toothed fungus (Hydnum coralloides), on the under side of a log. Original. Tooth fungi (Hydnacece). The fruiting body of the tooth fungus is in some respects more complex than that of the smooth shelves or clubs. The palisade surface is here distrib- uted over an area covered with teeth which thus increases the spore-bearing surfaces considerably. These teeth may be com- Minnesota Plant Diseases. 175 paratively short — one-half inch or less in some forms — or they may attain a length of three inches in others. They are chiefly wood-inhabiting saprophytes and comprise some serious timber rots and diseases; some are found on the ground. The coral fungus and the very similar bear's-head fungus are exceedingly common tooth-fungi, found on logs in autumn or throughout the summer. The fruiting bodies of most of these fungi are edible. (Figs. 81, 84, 119.) Pore fungi (Polyporacea). This is one of the largest of the groups of the palisade fungi and contains many of our most conspicuous forms. They are palisade fungi which have in com- mon the formation of pockets or pores in the fruiting body and on the surfaces lining these pockets or pores are found the pal- isades. A safe position and a great increase of spore area is thus effected. There is considerable variety in these fungi in respect of the consistency and form of the fruiting body. One alliance of forms has more or less gelatinous fruiting bodies in which ridges which cross and recross each other form shallow pores. Many of these gelatinous pore fungi have single, pros- trate fruiting bodies, though some form true shelves. Such gelatinous pores resemble many of the trembling fungi and their allies. To this group belongs the wrell known dry rot fun- gus which is probably the most dangerous timber-saprophyte known. They are common on rotting logs and stumps. The majority of pore fungi have totigh, leathery or more or less woody fruiting bodies of a true shelf-habit. Most of our com- mon shelf fungi belong to this group and they comprise a great many of our most common timber diseases. A variation is noticeable in the form of the pores and upon this variation is based in a large measure the classification of the numerous forms. Some pores are cylindrical pockets, others are elon- gated and often fuse with neighboring pores and thus form complex labyrinths; others, again, are hexagonal in outline. The pores, moreover, vary in depth, in their relationships to sur- rounding parts, in methods of formation, etc. Again, some shelves last but one year while others live from year to year, adding new substance to the fruiting body every year. In one alliance of forms the shelves may be branched, forming large compound shelves. The birch shelf-fungus, the sulphur fungus, 76 Minnesota Plant Diseases. Minnesota Plant Diseases. 177 and the tinder fungus, may be mentioned as a few of the numer- ous common forms of these pore fungi. In addition to the gelat- inous and tough and fleshy pores are the beefsteak fungi which are very soft ; in these the pores with, their surrounding walls are free from each other and look like small dependent tubes FIG. 8G. — A stick-dwelling gill fungus (Lenzites betulina), on a dead branch of a birch. Original. hanging from the fruiting body. Most of these forms are edi- ble. Somewhat similar to these are the species of Boletus, all of which are fleshy and grow on the ground, often in swampy places. The pores are here also found in tubes which separate from each other readily and the tubes are combined into a sep- arate layer. The pores are usually large and the fruiting body always possesses a central stalk and mushroom-like cap. On the under surface of the cap are found the pores. The pore surface is sometimes enclosed in young stages by a veil-like 12 178 Minnesota Plant Diseases. covering below which attaches the edge of the cap to the stem. At maturity this ruptures and a part of it remains at- tached to the stem as a so-called ring. They are all earth-in- habiting saprophytes and most forms are edible while a few are poisonous. (Figs. 5, 10, 36, 81, 85, 120 to 127, 163.) Gill fungi (Agaricacece). In this group of fungi the palisade layer is spread over structures known as gills. These gills are plate- or leaf-like bodies arranged on the under side of an um- brella-like cap and run from the stalk to the cap edge. When the cap is young the gills may be closely pressed together but are later spread apart to allow the spores to be shed. This group contains an enormous number of plants, be- ing by far the largest of the palisade fungi, and it includes not a few plants of economic importance. The fruit- ing bodies vary in size from not larger than a large pin to umbrella- like forms more than a foot in diameter. In consistency the fruit- ing bodies may be gel- atinous, waxy, fleshy, leathery or even woody. Some forms are stalked while oth- ers are attached direct- ly by their cap edges. In the higher forms the fruiting body possesses veil-like structures which enclose the gills or the whole cap as long as the gills are still immature. As soon as the spores are ripe the veil breaks, leaving a cup-like FiG. 87.— Shaggy-mane fungus (Coprinus comatus). This is an inky-gill fungus. The cap is seen to be blackened at the base, where the whole substance of the cap deliquesces and drops its black spores in an inky mass. Original. Minnesota Plant Diseases. 179 structure at the base of the stem or a ring-like fragment on the upper part of the stem. The gills are then exposed to the air and are ready to shed their spores. If the cap of such gill fungi be cut off, placed on paper and kept thus in a closed chamber, the spores will fall in such numbers as to give a very distinct map of the gills. The ^^gtiflffflRfffeBfe.) spores are of various colors, white, pinkish salmon, ochre- brown, dark-purple or black, and this color difference has been used as a basis for a classification of the gill fungi. In some dung-inhabiting forms the gills liquify when the spores are ripe and the latter drip from the plant in an inky fluid mass. Some caps when broken exude milky fluids of different col- ors : white, red or yellow. Such are known as the milk fungi. The great majority of the gill fungi are true sapro- phytes. Many are earth-in- habiting or dung-inhabiting and an enormous number are \vood-dwelling forms. These contain many of the chief tim- ber-rot fungi as well as many wound-parasites. A few ate The gill fungi find their chief economic importance, outside of their timber-rotting effect, and as agents in the decay of plant debris, in the food products which they furnish to man. The commercial mushroom is a member of this group and hundreds of wild forms are ed- ible. The latter are being used more and more extensively as food by those who take the pains to hunt them up and to know them. There are likewise some fungi of this group which are FiG. 88. — The shaggy-mane fungus. This fruiting body is in a more advanced stage of deliquescence than that shown in Fig. 87; almost the entire cap has dripped off. A ring (annulus) is seen at the base of the stalk. Original. parasitic on other gill fungi. [8o Minnesota Plant Diseases. .2+3 «a ol Is !- y _cn ^ » "" Minnesota Plant Diseases. 181 exceedingly poisonous and fungus eaters must take good care that they are familiar with the poisonous varieties found in the state. (Figs. Frontispiece, 6 to 8, 10, 18, 20, 81, 86 to 89, 116, 128 to 132.) Puff-balls and their allies (Gastcromycctcs). All of the re- maining basidium-bearing fungi have closed fruiting bodies. The basidia are borne inside of this structure either in palisades lining the surface of chambers or in irregular fashion on loose threads throughout the fruiting body. The latter arrangement FIG. 90. — A group of the common gemmed puff-balls (Lycoperdon gemmatum) just before opening; the position of the future opening is seen at the darkened tops of the fruiting bodies. Original. is prevalent in the wefted puff-balls (including the first, second and third of the following groups), while the remaining groups possess the palisade arrangement of basidia. The fruiting body always possesses one or more covering membranes. These fruiting bodies may remain closed until the membranes de- cay, when the spores are released, or they may open in charac- teristic ways, by pores or by splitting, and thus allow of the es- cape of the spores. In most forms the interior of the fruiting body partially disintegrates, leaving only the spores in a fine dust held in a loose weft of long and strong threads which give the in- terior a sponge-like texture. The spores are then thrown out in 182 Minnesota Plant Diseases. dust-like clouds or puffs and are caught by the wind and may be transported considerable distances. The chambers with their palisade lining are not seen in the mature fruiting body and can only be observed when the latter is young. The inte- rior is then fleshy, white and more or less solid, and with age gradually gets yellowish-green and soft, and even semifluid, finally producing the dust of spores in the thread weft. (Figs. 81 to 91, see also following seven groups.) FIG. 91. — The same group as in Fig. 80, taken two weeks later; shows the opened puff-balls. Original. Long-stalked puff-balls (Tulostomaca?). One frequently meets in sandy places and in open fields groups of small puff- balls about one-half to three-fourths of an inch in diameter, mounted on long stalks which in some cases attain a length of six inches. At maturity the spores form a powdery dark brown mass and are thrown out through a pore in the puff-ball wall. The puff-ball is formed just under the surface of the ground and is raised up above the ground by the somewhat rapid growth and elongation of the stalk, so that the puff-ball is elevated to an advantageous position for the scattering of spores. The mycelium forms strands and the fungus is an earth-dwelling saprophyte. (Figs. 3, 81, 92.) Minnesota Plant Diseases. 183 Hard skinned puff-balls (Sclerodermatacecu). Many of these puff-balls form their fruiting bodies at least partially under- ground. The coat is hard and leathery in texture and usually opens by splitting in some irregular fashion. The spores also form a powdery mass which in our common species is dark vio- let in color. The fruiting bodies are usually large in size, at- taining a diameter of five and six inches in many cases. In their immature condition they are superficially not unlike potatoes in appearance. These fungi are also earth-dwelling sapro- phytes. FIG. 92. — Stalked puff-balls (Tulcstoma mammosum). The puff-balls have been raised from the sandy ground on stalks just before the opening and shedding of spores. Original. Sphere-throwing fungi (Sphacrobolacccc}. These are very minute fungi and not easily recognized as puff-balls. The fruit- ing body is usually not more than three-sixteenths or one- eighth of an inch in diameter and covered with a soft whitish outer coat. Inside of this is an elastic covering which, at the maturity of the spores and after the outer coats have been split, inverts and forcibly ejects the whole mass of spores. The latter remain attached together in a solid sphere and never form a powdery mass. The sphere may be thrown as far as six feet 184 Minnesota Plant Diseases. into the air. The spores begin to germinate in the mass and thus a new mycelium is started. These fungi are wood-inhabit- ing saprophytes and are frequently found on pine wood, as "on decaying sidewalk planks. (Figs. 14, 81.) Underground puff-balls .(Hymcnogastracccc). These fungi form their fruiting bodies under the ground, sometimes an inch or more below the surface. They are often thick-skinned and never open except by the decay of the walls. The interior does not develop a spore-powder mass but remains chambered to maturity, and the chambers are lined with palisades of basidia. These fungi are saprophytic. They are not abundant in Minne- sota though several forms are known. They resemble very much the true and false truffles, but, of course, differ from these in the method of forming spores, for the puff-ball spores are never found in sacs but always on a basidium. True puff-balls and earth-stars (Lyco per dine ce). This group includes many exceedingly common fungi which can be found in great abundance in early fall. The puff-balls are therefore very familiar objects. The fruiting body is usually spherical and is always at least at maturity found on and never below the surface of the ground. It is usually provided with at least two coats, the outer of which is shed in various ways and the inner coats peel off, undergo splitting, or open by a definite pore-like aper- ture. In one group of very common puff-balls, the outer coat forms small bosses, or more or less elongated spines, which at maturity fall off (Figs. 90 and 91) and leave characteristic scars on the inner coat. One of the most familiar of this group is the gemmed puff- ball in which the short spine-bosses are grouped together in clusters. Some true puff-balls have paper-like and very thin coats and our common form of this group is almost perfectly spherical. The outer coat peels off in shreds and the inner opens by a pore. In still other forms the puff-ball's outer coat splits along the equator and the upper half then becomes in- verted and looks like a saucer containing a puff-ball. The puff- ball fruiting body always contains its spores in a powdery mass which lies loosely in a cotton-like tangle of sterile threads. When jarred in any way the puff-ball emits clouds of spores which look like dust, olive-green, brown or black-purple, as Minnesota Plant Diseases. 185 the case may be. The distribution of the spores may thus con- tinue for an unlimited period. Of course wind is the chief agent of distribution. The earth-stars are puff-balls with usu- ally three coats in the wall of their fruiting bodies. The outer falls off and the median coat splits from the tip nearly to the base in a number of places and each lobe, so formed, bends back when it absorbs water, giving to the fruiting body the form of a star. By this bending back of the lobes the puff-ball is broken loose from its mycelium and raised up in the air. Thus the FIG. 93. — Earth-stars. (Geaster triplex.) The uncovered strand mycelium of this fungus is seen to the right, below; in the center and to the right above are unopened fruiting bodies; above in the center is a star, just opening, and below to the left is a fully opened or vaulted star with opened puff-ball in the center. Original. spores obtain a more advantageous position for distribution. In most earth-stars this vaulted condition is permanent but in one form (really, however, a wefted puff-ball) the coat opens and closes depending on the presence or absence of water. The bending back of the lobes is affected by the greater swelling which takes place in the inner threads of this coat while the outer threads are tough, remain somewhat rigid and are not greatly extensible. One Minnesota earth-star which in the younger stages is found just below the surface of the leaf mold is able to lift itself out of the mold and becomes vaulted directly 1 86 Minnesota Plant Diseases. over the hole from which it was torn loose. The puff-ball fruit- ing body in the very young stages is internally fleshy, more or less solid, and usually pure white, and in this condition is edi- ble and frequently sought by mushroom eaters. Caution must be exercised to prevent mistaking for them the young button- like stages of the poisonous gill fungi, which are not at all un- like certain puff-balls. Puff-ball fruiting bodies vary enormous- ly in size. The smallest are little larger than good-sized peas while the giant puff-ball, a form much sought for by mycopha- gists, has been frequently collected in Minnesota a foot or more in diameter. In the youngest stages the interior of the puff- ball is chambered and the chambers are lined with a palisade of basidia. The mycelium of certain puff-balls has been de- scribed as furnishing the mycorrhizal threads which live in part- nership with roots of certain trees. These fungi are otherwise saprophytic in habit. (Figs. 10, 81, 90, 91, 93.) Birds' -nest fungi (Nidulariinece). This group of basidium- bearing fungi would at first sight be scarcely recognized as a close relative of the puff-balls. Such it is, however, with pecul- iar variations from the typical puff-ball structure. The cham- bering here becomes permanent and the chambers are lined as usual on the inside with a palisade ; they become separated by the breaking down of the threads between. The chambers thus come to look like small hard-coated egg-like bodies, which lie loosely within the walls of the puff-ball. These walls open at the apex by a broad-mouthed opening, which in the earliest stages is closed by a parchment-like membrane, so that at ma- turity the fruiting body has an open beaker-like form. In the beaker or cup lie the egg-like chambers. The latter are in our commoner forms attached to the wall by thin stalks of exceed- ingly elastic fungus threads which are so extensible that in wa- ter they can be drawn out to a length of six inches or more from one-fourth inch or less in the dry state. This stalk may serve to attach the fungus to the legs of insects and again from here to the twigs or trunks of trees. The stalk is somewhat gel- atinous which aids in the fastening of the stalk. The spores are thus distributed in packets, which are the separated chambers, and they germinate directly from the interior of the chambers. The birds'-nest fungi are saprophytes with chiefly wood- or Minnesota Plant Diseases. dung-dwelling habits. They may exist as timber rots but are seldom if ever abundant enough to cause serious damage. (Figs. 13, 81.) Carrion fungi (Phallinece). More unrecognizable still as puff-ball relatives are the car- rion fungi. In the very early stages of the fruiting body, however, this relationship be- comes somewhat clear. The mycelium usually forms whit- ish strands and upon these strands arise the fruiting bod- ies as small spheres or pear- shaped objects and as they in- crease in size look superficial- ly very much like puff-balls. These "eggs" attain a size of three or four inches in some forms, while in others seldom exceed a filbert nut. The tip of the "egg" is usually just at the surface of the ground. The outer coats of the "egg" enclose a great gelatinous mass and at maturity this swells up and the outer walls break. There then emerges from the "egg" a stalked body with a terminal cap. The stalk elongates rapidly from a compressed condition in the "egg;" the elongation is not growth but a straightening out of folds, much as a sponge enlarges when it absorbs wa- ter. The carrion fungus cap is thus raised several inches into so that the elongation is delayed FIG. 94. — A carrion fungus (Dictyophora ravenellii). Below are seen the rem- nants of the "egg" coverings which have been broken and remain as a cup around the base of the stalk. The Jatter is seen to be spongy; by straightening out from a compressed condition it has lifted the cap som.* inches above the ground. The cap has still a considerable spore mass left; insects have, however, carried off the lower portion of the spore mass. The odor of the latter is that of badly decayed carrion. Original. the air in a few hours or less, until the spores are ready for i88 Minnesota Plant Diseases. distribution. The spores are found on the upper surface of the cap and at maturity are contained in a sticky, semi-fluid olive- green mass which has a strong odor of carrion. Flies and other insects are attracted by the odor, carry off the sticky mass, and thus disseminate the spores. The attraction for insects is still further increased by the presence in some forms of a lace-cur- tain-1 ike veil which hangs down from be- neath the cap. In the very early stages the spore-bearing region shows a series of cham- bers lined with pali- sades and very similar to that of the puff- balls, but at maturity the chambers disap- pear in the disintegra- tion of portions and only the sticky remains with the spores are left. The carrion fungi show an extraordinary amount of differentia- tion and complexity in the development of their fruiting bodies and the insect-distri- bution of spores is car- ried to a high degree of efficiency. In these respects the carrion fungi are undoubtedly the most highly de- veloped of all of the basidium-bearing fungi, and it is doubtful if any other forms in the whole realm of the fungi are their equal. The carrion fungi are saprophytes and are all earth-dwelling forms. (Figs. 3, 10, 12, 81, 94, 95.) FIG. 95. — A carrion fungus (Dictyophora duplicata), photographed just after the breaking of the "egg" and while the cap was being lifted. The "egg"- membrane remnant at the base is in sharp focus since it did not move during the exposure; but the whole top which has been lifted during the 15-minute exposure has been blurred. Below the cap is a large lace-curtain structure which serves as an additional attraction for insects. Original. Chapter XIII. Other Disease-causing Organisms. Bacteria. One does not usually associate bacteria with dis- eases in plants, but they are nevertheless frequently agents of such disease. In recent years many diseases of bacterial origin have been discovered and described. Man's chief inter- est in bacteria is usually centered in the diseases of man which are so largely caused by bacterial action. The bacteria were formerly considered to be fungi but in recent years it has been recognized that they are most closely related to the blue-green algae, though they differ from the latter in important points. They resemble the fungi in their mode of nutrition — for they ob- tain their food in a partially elaborated condition and, with a few exceptions, are unable to manufacture starch from air, gases and water as do green plants. They are therefore devoid of leaf green just as are the fungi, and thus differ from the blue-green algae. They may possess coloring matters of various kinds but are not as a rule able to utilize these in the conversion of the sun's light to energy in starch manufacture. They differ from the fungi, however, in their method of growth and division, and in these re- gi*( Bac- of black spects and in general appearances resemble most o> s e udomonas closely the blue-green algae. The bacteria, then, c a m p e s t ris). . They are seen to may be considered as dose relatives of the blue- be tmv cylin- ders< -CHJ gAhJ y green algae which have adopted fungus habits magnified. After of nutrition. The forms and sizes of bacteria. The bacteria are all ex- ceedingly minute plants consisting of single cells. They may be less than one thousandth of a millimeter in length and the largest are seldom more than about ten-thousandths of a milli- meter. It requires, therefore, microscopes with powers of high Minnesota Plant Diseases. magnifications in order to observe and study them. The bac- terial plants may differ somewhat in form and to these various forms names have been applied, and upon them the classi- fication of the bacteria was formerly based. It is now rec- ognized, however, that several forms may appear in the same life-story under differences of conditions, thus rendering the former classification unsatisfactory. An approximately spheri- cal bacterium is known as a coccus, a short, rod-like form is known as a bacterium, in the narrower sense, and the long rod form is a bacillus. Some forms are, moreover, comma-shaped ; others are undulate or wavy in appearance, while still others ap- pear much like corkscrew or long-drawn spiral coils. These plants may differ, moreover, in the manner in which colonies are formed. All bacteria in the broader sense multiply chiefly by simple division of the cell into two, the resulting parts split- ting away from each other — hence the name fission plants. By such divisions filaments of cells may be built up, or by division in two planes, plates of cells, or when division in three planes takes place masses of cells are produced. As the external walls of bacteria are frequently gelatinous, sheaths are formed which serve to bind the plants together in such filaments, plates or masses. A larger gelatinous colony may thus be built up and is then known as a zoogloea. One sees among the bacteria a great variety of habits; a large number inhabit fluid media. As a special means for dissemination many of such forms have lash-like projections of the protoplasm which whip around in the water and propel the plant cell about. Multiplication and reproduction. The fission method of multiplication which is common in the bacteria is a very effi- cient one. It is also common to certain groups of blue-green algae. In bacteria the successive splittings into cells may fol- low with some rapidity, e. g., under the most favorable condi- tions the hay bacillus completes a division in twenty minutes. It has been calculated that if a bacillus two-thousandths of a millimeter in length were to divide uninterruptedly at the rate of once every thirty minutes, at the end of five days the volume of the resulting bacteria would fill all of the ocean beds of the globe. Competition and unfavorable conditions, of course, prevent such disastrous results, but the possible rapidity of Minnesota Plant Diseases. multiplication is thus well illustrated. When unfavorable con- ditions confront a rapidly dividing bacterium, spore formation may take place. The spore, just as most fungus spores, pro- vides itself with thick walls and is thus protected during the continuance of the unfavorable surroundings. These spores may be formed inside of the cells, or by the mere transforma- tion of the ordinary cells by wall thickening and condensation of protoplasmic contents. When placed again under favorable conditions the spore may grow out in various ways into the ordinary bacterial cells. No breeding act is known among the bacteria. Physiology of bacteria. The physiological activities of the bacteria are most varied and interesting. They are of immense economic importance for upon them are built a host of indus- trial processes as well as many diseases in man and in plants. Many geologic deposits, as iron ores, may possibly owe their existence to bacterial activities. Air-loving and air-shunning bacteria. Most bacteria resem- ble other plants in their requirements for air gases during their life processes. Oxygen, one of these gases, is utilized in burn- ing up certain compounds and in this combustion energy is liberated to run the protoplasmic machinery. This use of oxy- gen is common to animals as well as plants and the ultimate products of the burning are carbonic acid gas and water. Such bacteria may be known as air-loving bacteria or perhaps, more strictly speaking, oxygen-loving. There is another class of bacteria which is capable of obtaining such energy as the air- loving bacteria derive from combustion of compounds in a dif- ferent way, viz. : by the breaking down of complex organic compounds into simpler, during which process the necessary energy is liberated. This process may take place, moreover, when no air is present, and in certain cases the exclusion of air, and particularly of oxygen gas, is necessary. Such bacteria are known as air-shunning bacteria. They have a method of break- ing down complex substances different from that of the com- bustion method and may carry on such a process even when the air is entirely excluded. Among the many air-loving forms the vinegar bacteria may be mentioned while the rancid-butter bacteria are examples of air-shunning kinds. 192 Minnesota Plant Diseases. Influence of external forces as light, temperature, etc. It is a well-known fact that most bacteria do not thrive in sunlight but that the direct rays of the sun are fatal to them. Too much stress cannot, therefore, be placed upon the necessity for sun- shine in thorough processes of sanitation. Waters of lakes and rivers are largely purified by direct sunshine which can fatally affect bacteria to a depth of several feet below the surface. Of course this is not the only agent of "purification but is one of the most important. It is to be expected, therefore, that when bacteria cause disease in plants it is in the underground por- tions, as bulbs or roots or stems, or in situations where the illu- mination by the sun's rays is always poor. Excessive moisture may, moreover, aid in bacterial dissemination. The bacteria are easily carried about in the water currents especially if they have the whip-like swimming apparatus which is common among so many forms. Some bacteria can live and even reproduce in temperatures near the freezing point, while the resting, inactive cells are often capable of resisting very much lower temperatures. On the other hand, heat-loving bacteria are known which thrive in comparatively high temperatures — even fifty degrees Fahr. above blood heat. The bacteria are thus seen to enjoy wide extremes of temperatures. A given species, of course, has usually a much more limited range and always possesses a favorite temperature at which it grows best. In general, bac- terial cells in the dry state are capable of enduring higher temperatures than those in the moist condition, — facts which are used to advantage in combating bacterial disease germs. In the canning of fruits, for instance, boiling for a short time will destroy most germ cells though spores will often re- sist even such harsh treatment. The power of resistance in the dry state is an important feature, for bacterial germs may live for months and even years in such conditions, germinating again as soon as favorable conditions of moisture and nutrition present themselves. Thus germs of various diseases of man may lurk in the air or soil, becoming evident only upon the ad- vent of suitable conditions. Strong electric currents usually destroy bacteria and this fact has led some to believe that elec- tricity may be utilized in the purification of municipal water supplies. Minnesota Plant Diseases. 193 Bacterial partnerships and antagonisms. Bacteria often form dense colonies of individuals developing in gelatinous masses. These bacteria may all be of one kind, but frequently are different, and may then live in a partnership apparently ben- eficial to each other. It is evident that such forms do not com- pete with each other for food stuffs. Bacteria may also form partnerships with other organisms as with yeast plants. In such cases the waste products in the nutritive processes of one may be food for the other plant and thus a beneficial partnership is established. Such is the association of bacteria and yeast in the English ginger beer "plant" and in the production of other drinks as the Asiatic kephir. Such a partnership is also ex- plained in the fact that organisms of this kind often form waste products which, if allowed to accumulate, may prove detri- mental to the organism producing them. This is a common method by which bacterial growth is limited. These com- pounds are in the case of bacteria often poisonous and form the toxins which in disease germs are the poisoning agents of the disease. The accompanying organism of a partnership may use up and remove these detrimental substances and thus allow the first partner unhindered development. Antagonism of bac- teria in colonies may result from competition for food materials or from the production of substances by one, which are poison- ous to the other organism. Disease-causing bacteria. One of the most useful classifications of bac- teria is the arrangement of forms ac- cording to their prominent physio- logical effects. In such an arrange- ment the disease-causing or patho- logic forms are of great economic im- portance. These are the forms which give rise to most of the well-known diseases of man and lower animals. FIG. 97.-Bacteria of fire-biight of Cholera, tuberculosis, diphtheria and apples (Bacillus amylovorus). fv^l^JH Qr~ Knf Q f~™7 ^f fUP Hp^trnr Highly magnified. After B. OP11 a are DUt a ICW OI me aCstrUC- tive diseases of bacterial origin. By an accurate knowledge of the life-story, physiology, etc., of these organisms preventive measures of sanitation and quaran- 13 194 Minnesota Plant Diseases. tine have been made possible and an enormous saving of life effected. Modern methods of medical and surgical practice have been built upon such knowledge. Great as have been the results in the past, still greater may yet be achieved in the future by a more complete knowledge of these disease-causing bacteria. This applies as well to those bacteria-causing diseases of plants as to the diseases of man, though the former are not so numerous nor so vital to man's interests. Dye-forming bacteria. Another great group of bacteria have the peculiar property of producing coloring matters dur- ing their nutritive processes. This coloring matter is in some cases found in the cells of the bacteria and in others is a by- product of nutrition. Red and yellow spots on bread are fre- quently of this nature and milk is sometimes colored red from a similar cause. The blue coloration of milk is also of bacterial origin. Certain bacteria form a beautiful "bacterial purple" and are furthermore peculiar in that, by means of this color- ing matter, they seem to be able to utilize the sun's rays in a manner analogous to the leaf-green plants which convert sun- light energy by the use of leaf-green. The production of in- digo dyes from indigo plants is also dependent upon the activ- ity of bacteria; other blue colorations, as in certain kinds of cheese diseases, and again, green colorations may have bacterial origins. Light- and heat-forming bacteria. In the conversion of energy in which bacteria are engaged, many forms exhibit still other peculiarities. Some utilize surplus energies in the generation of light and such produce phosphorescence or other illuminations. Sea phosphorescence is in part due to these bacteria. Others again dissipate energy in the produc- tion of heat and examples of these may be seen in heated manure piles, in silos, in certain methods of curing hay, and in tobacco curing. The generation of heat in all of these cases is due to the activity of heat-producing bacteria. The tem- perature may even be raised to such a degree that rapid com- bustion of the materials may take place and such occurrences are usually described as spontaneous combustion. Fermentation bacteria. Still another great group of bac- teria are capable of causing fermentation in fluids — a splitting Minnesota Plant Diseases. 195 up of compounds accompanied by the production of gases just as is effected by yeast plants in bread- and beer-making processes. These fermentation processes are of many kinds. Butter becomes rancid and milk may be broken up and soured by the action of these bacteria. Upon the action of milk-fermenting bacteria depend other processes in certain methods of curing hay and ensilage. Again, fermenting bac- teria are the agents of fermentation in the production of vin- egar. Nitrifying bacteria. Of great importance in agriculture are those bacteria which live in the soil and by their action prepare crude materials for leaf-green plants. The latter re- quire a certain gas known as nitrogen which must be fur- nished, however, in a particu- lar kind of compound known as a nitrate. Leaf-green plants are unable to utilize nitrogen gas in the free state and this is the condition in which it exists in the atmos- phere. Now the nitrifying bacteria are capable of using compounds unavailable to the leaf-green plants and by the united action of several bac- teria finally build up the ni- trates desired by the leaf-green plants. Nodule bacteria. Certain plants such as clover and many other plants of the pea family form small nodules on their roots. In these nodules dwell bacteria, which are capa- ble of using free nitrogen from the air. They then pass the manufactured nitrates on to the clover plant. These nod- ules are therefore special habitations for nitrogen-fixing bacte- ria, wThich are thus protected and fostered by the clover plant. FIG. 98.— Bacterial nodules on root of com- mon bean. In these swollen portions of the roots are found bacteria which as- sist the plant in obtaining nitrogenous food material. Original. 196 Minnesota Plant Diseases. The latter derives its benefit in the nitrate product. A true part- nership is thus effected. Clover and alfalfas and all such nodule- possessing plants are therefore valuable rotation crops because they accumulate by the aid of their bacterial partners nitrates, where wheat or other crops have depleted the soil of these com- pounds. These bacteria are now distributed by the Depart- ment of Agriculture in quantity for sowing on poor soils where leguminous plants as clovers, etc., are then grown. Such soils can thus be greatly enriched so that other crops which do not possess bacterial nodules can subsequently be raised. Other economic phases bacteria. A great many other phases of bacterial life are of importance in the arts and industries and only a few may be mentioned in this short review. In tan- FIG. 99.— The bacteria of such root nodules of ning, in diseases of wine and the pea family as are shown in Fig. 98. U^r r^nri^f <-nrrl1in cr in rVi^ On the left of Vicia sativa (the spring beer> rennet Curdling, in tllC vetch), on the right of Medicago denti- rrmtlifnlrl nrnrpc^pc; nf nntri- culata. Very highly magnified. After At- kinson- faction of organic matter, in cheese industries, in the deposition of bog iron ore, the bacteria appear in important roles. More particularly are we here con- cerned with those forms which attack living plants and cause disease. Such plant diseases are not numerous but investiga- tion is steadily adding new examples and they promise to be- come of sufficient importance to make this brief general dis- cussion of this group of plants justifiable. The various bacte- rial diseases will be considered individually in subsequent chap- ters. (Figs. 96 to 99, 172 to 178, 195). Slime molds (Mycctozoa). This group of organisms is now commonly classified with the simplest animals, though they are very fungus-like in many of their characters. Most slime molds are true saprophytes but a few have adopted para- sitic habits. Some of the latter live in plants and others in ani- mal tissues. The slime molds produce spores in structures very similar to the fruiting bodies of many saprophytic fungi. These fruiting bodies are usually very small — many are of pin-head size but a few attain a diameter of six inches. The spores are Minnesota Plant Diseases. 197 1 usually enclosed in cases which have definite methods of open- ing. The spore mass is dusty or smut-like and the spores are tiny spheres of microscopic size. If the spores be placed under favorable conditions of moisture and temperature they do not send out a fungus thread as do true fungus spores, but the wall breaks and the protoplasmic con- tents emerge in a naked mass, not unlike a very tiny drop of al- bumen in appearance. This small mass creeps about by changing form, engulfs food, and lives in all essentials as do other very simple animals. After a time a large number of these ani- mals of the same kind meet and soon fuse together forming a larger mass of jelly-like material which is known as a plasmodium. The plasmodium is often met with on the forest floor or in other moist places and is often highly colored. Pink and yellow are common colors though many are yellowish white. The plas- modium may be cake-like or may be drawn out in various ways, as into strands. It is in reality a colony of slime-mold animals, and this colony may move and feed and otherwise behave as a simple animal. After a time and particularly as the atmosphere becomes dryer the plasmodium draws itself up into some kind of a fruiting body which is often composed of stalk and capsule. In the latter are found the spores and also sterile threads, in appearance not unlike those found in FIG. 100. — A slime mold. 1. An opened (on right), and an unopened fruiting body. From the opened fruiting body is seen a protruding fluffy mass of threads (capillitium), which encloses the spores as in a mass of cotton. 2. An isolated thread of the capillitium and a spore (highly magnified), (Ar- cyria serpata). 3. a, young snore (Chondrioderma difforme) ; b the same, germinating; contents are emerging as a naked bit of pro- toplasm; c same in the free swim- ming stage; has a single swimming lash; d same in amoeba stage; e sev- eral amoeba-like masses fusing to form a small plasmodium; f a young plasmodium. 2 and 3 highly magni- fied. 1 and 2 after DeBary; 3 after Cienkowski. 198 Minnesota Plant Diseases. the fruiting bodies of puff-balls. In fact many of the fruiting bodies resemble so closely the true puff-balls that botanists for- merly classified them as such and the amateur is constantly de- ceived by the resemblance when he first meets with these forms In the field. When the fruiting body is formed the entire plas- modium is used up in its construction and the spores are blown about by the wind and thus disseminated. The slime molds exhibit, therefore, a lowly method of animal life and a fungus- like reproduction. The slime molds, living as plant-parasites, live in the cells of the host plant and do not form fruiting bodies like those of the true wood-dwelling saprophytes. One slime mold parasite causes the club root of beets living in the cells of the swollen portions. The slime-mold parasites of animals cause various diseases. Malaria is due to a slime mold which lives a part of its life in the body of the mosquito and is trans- ferred to man in the bite of the insect. Texas fever of cattle and several diseases of man are traceable to the action of organ- isms of this slime-mold group. (Figs. 100, 179,180.) Other kinds of plants as disease-causing organisms. As has already been stated, fungi constitute an overwhelming majority of those plant diseases which are of plant origin. Besides these and the bacterial diseases, a few are known which are caused by other kinds of plants though they are with few exceptions of slight economic importance. Only a short account of them will be permissible in this work. Algae. A number of blue-green algae live as place parasites in cavities and tissues of higher plants. Such are doubtless not true parasites in their nutrition but their position in the tissues of the host offers them protection of place and a safe harbor. Such are found in floating water-ferns, and in the roots of the greenhouse sago palms. Some flower-pot algae are also place parasites. The posses- sion of leaf-green enables them to manufacture their own food. A few such green algae are known on water-inhabiting seed plants, e. g., several species of the tiny duck weed. No diseases of economic importance are known in these groups. Mosses and fernworts and lower seed plants. No Minne- sota members of these groups of plants or of their alliances are known as parasites of other plants. Some of the latter groups Minnesota Plant Diseases. 199 have already been mentioned as living in an unequal partner- ship with root fungi in which the green plants are the dominant partners. They are not however found as parasites on other green plants. Higher seed plants. A number of Minnesota species of the higher seed plants are known as true parasites on other leaf- green plants and a few of these are of economic importance. When a race of plants which was originally self supporting by FIG. 101 — Twig of a witches'-broom of spruce, showing the parasitic plants of the mistle- toe which cause the "brooming" of the branches. The mistletoes are seen as very small plants, scarcely larger than the spruce leaves; they are tipped with an egg- shaped body which is the fruit of the mistletoe and contains a single seed. (See also Figs. 24 and 25.) Photograph by the author. means of a leaf-green apparatus, enters upon a parasitic life, the leaf-green mechanism falls into disuse and may suffer reduction or may even entirely disappear. Hence we find in confirmed parasites of this group more or less of a bleaching of the para- site. They are often, therefore, yellowish in color and the leaves are reduced to mere scales or are wanting entirely. 2OO Minnesota Plant Diseases. Special kinds of sucker roots are frequently produced which penetrate the host plant tissues and absorb the manufactured food stuff. Some of these parasites have only half learned the parasitic habit and still retain some of their leaf-green apparatus. A typical parasite of this group of plants is the little mistletoe which occurs in great abundance on spruce trees in the north- ern part of the state. This little plant lives in the twigs and larger branches of the spruce and induces the formation of witches'-brooms. Badly diseased spruces therefore show a very irregular contour and may eventually be killed. The common dodder is another confirmed parasite. It starts life from the seed as a little leaf-green-possessing seedling but as soon as it comes into contact with a suitable host plant it abandons its leaf-green apparatus and coils itself closely around the support, sending in its sucker roots which also serve to fasten it to its support. The twining stem grows rapidly, bears very small and reduced leaves, and the whole plant is yellowish in color. The dodder is common on many wild swamp plants and is also occa- sionally abundant on clover where considerable damage may be caused. Of some interest are also those few forms which are root parasites. The toad flax, which is a common Minnesota plant, has partially learned this habit of parasitism. Here the plant is apparently a typical leaf-green herb, but its roots may be found penetrating the roots of other plants and there obtain- ing nourishment. Parasitism is here an auxiliary process. Other Minnesota plants, members of the broom-rape family, have completely learned the root parasite habit and have con- sequently lost all of their leaf-green. The stems are usually small, reaching but a short distance above the ground, and bear a few colorless reduced leaves and spikes of flowers. Several species of cancer roots and broom rapes occur in this state. They are not abundant, however, and produce no far-reaching or destructive disease in plants. (Figs. 24, 25, 101.) Chapter XIV. Economics* Prevention and Cure. Jff The economic importance of plant diseases. A few well- known figures will illustrate the great economic importance of the fungus diseases of plants. These include only estimates of epidemics. From the nature of the case it is impossible to esti- mate the smaller losses due to sporadic diseases which have probably caused more total loss than the great epidemics. In the kingdom of Prussia the year 1891 was particularly favorable for the rust disease of cereals. In that year the loss of wheat, rye, oats and barley from rust has been estimated at over one hundred millions of dollars. In Australia in 1890-1891 the loss by wheat rust was estimated at twelve millions. In California the grape disease from 1884-1886 caused an estimated loss of twenty million dollars. A single English tomato house has in one season suffered a loss of a thousand dollars by fungus dis- ease. An agricultural expert has estimated the yearly loss in the United States due to loose smut of oats, before successful treatment was discovered and introduced, at eighteen million dollars. One of the most striking illustrations of the enormous losses due to fungus diseases is found in the history of the coffee leaf-rust disease which has played such havoc in the east- ern hemisphere. It has practically exterminated the coffee plantations of Ceylon where the loss from about 1870 to 1886 was about five million dollars yearly and the total loss in those years from sixty to seventy-five million. India's annual loss from wheat rust has been estimated at from two to ten million. In the United States loss by wheat rust for 1891 has been placed at sixty-seven millions of dollars. In our own state Dr. Lugger, the late state entomologist, estimated the loss from wheat rust in Minnesota in 1888 as far in excess of the total loss by ravages of all insects including even the dreaded grasshopper. One can realize the enormous loss from this source in an estimate by 2O2 Minnesota Plant Diseases. officials of the United States department of agriculture, which placed the loss in the whole United States in 1882 on all agri- cultural products due to insects' ravages at 200 to 300 millions of dollars. No estimates are readily available for losses on smaller epi- demics nor on local ravages of fungus pests where conditions have favored a restricted epidemic. It is well known, how- ever, that the potato disease in certain wet seasons causes enor- mous losses, particularly in eastern states and in Europe. In the few years following its introduction in about 1845 the losses amounted in many places to a complete destruction of the po- tato crop. Garden truck and orchards yearly suffer in almost all sections of the country. In many cases the losses are not deemed important, but though slight, amount to great sums in the aggregate. We hear of rust-free seasons for grains but no year is absolutely free and such small unnoticed loss has come to be accepted as an inevitable tax upon grain. It is against such losses as well as against the great loss by epidemics that attention will have to be directed. It must be clear from the above figures that the fight against fungus diseases is not a mere illusion entertained by a few enthusiastic specialists but is a most important and vital economic feature of all future branches of plant industries. Prevention and cure. If there is one thing which will con- tribute more than any other to the relief of agriculturalists and horticulturalists from the losses incurred by the disease of plants it is knowledge. No one would hesitate to affirm that more extensive knowledge of the real nature of the diseases of man has lessened enormously the destructive attacks of those diseases. The force of this analogy is comprehended by few in its application to plant diseases. The practical plant grower wants to know only the cures, — sprays or whatever they may be, — he often does not care to study or learn the details of the disease-cause and its mode of action. But it is only with this knowledge that an intelligent application of remedial measures is possible. Probably no two occurrences of a plant disease have exactly similar conditions. The generalities which under- lie them are to be found only in a knowledge of the action of the disease-causing organism. The details of treatment must Minnesota Plant Diseases. 203 necessarily differ and the judgment of the operator is always im- portant. The value of that judgment is measured only by his knowledge. The more he knows of the causes and action of the disease the more intelligently and the more successfully will he be able to combat it. The various remedial measures — solu- tions, formulas, sprays and spray machinery — are all important, indispensable in fact — but they are not the ultimate object; they are the means by which relief is secured and the observant operator who knows what he is doing and why he is doing it has many more chances of success than he who is following book rule. I shall deem myself eminently successful in this work if I shall be able to contribute to such a spread of useful knowledge as shall fortify the efforts of all plant growers in the state. The solutions of these problems lie largely — I might al- most say entirely — with the men who are the operators. The ob- ject of this work is to help him to an understanding which will give reason and intelligence to his efforts. It is obvious, of course, that an objection will immediately be raised, viz. : the farmer cannot hope to master all of the details of the life-stories of disease-causing organisms — his time is occupied with the practical problems and operations of plant growing. And this objection has much of truth in it. Nevertheless, success in all lines is becoming more a matter of knowledge. What the farm- er can do and must do is to know more about the plants with which he has to deal — and these include not only his wheat and apples but the enemies of these plants as well. He must pick out from the results of those who have worked out and de- scribed the details of disease such facts as are of use to him and apply those results. Successful agriculture is no longer the simple method it was of old, i. e., the planting of the seeds and the trusting to provi- dence for favorable conditions of growth and produce. It is the scientific control of those conditions. The farmer alone stands helpless. The plant pathologist is an absolute necessity in the agriculture of today. His results must increase the efficiency of the farmers' efforts and they will if they are intelligently ap- plied. In this specialization the plant pathologist is by no means independent. He is just as dependent upon the coopera- tion of the farmer as the latter is upon him. In other words, 204 Minnesota Plant Diseases. both branches of this new agricultural machinery must work to- gether in order to achieve successful results. The facts of ac- tion and nature of diseases are useless unless applied and the application of such knowledge is in the province of the plant growers. In a word, the field of the plant pathologist is the enlargement and spread of knowledge of diseases and their causes and the field of the farmer is the application of such knowledge to the raising of plants. Both parts of the machin- ery of this new agriculture must work in harmony or both be- come useless. The successful plant grower must not only know what to do for certain diseases but why he does it, and the pathologist only can tell him why. On the other hand, the pathologist must look to the farmer for the solution of the countless problems of practical detail in the application of that knowledge. Every one knows that the best way of fighting off disease in man — as in typhoid, tuberculosis, etc. — is to prevent infec- tion, and just so with plant diseases. Prevention is the most successful treatment of disease. But how can a disease be pre- vented unless one knows the nature of the disease? It must not be supposed that no relief is possible from actual disease in plants for much can be done to furnish such relief but it needs no argument to convince a fair-minded grower of plants that prevention is more to be desired than methods of cure. It will therefore be convenient to consider the methods for combating disease under the two heads of prevention and cure. Prevention. Since prevention is of such great importance it is obvious that a disease must be anticipated — headed off — before it can get a start. Now the first stage of a fungus dis- ease lies in the infection. Infection, as has already been point- ed out, may be effected by fungus spores, as in rusts and smuts, or by the established mycelium, as in timber and wood rots. The prevention of infection is therefore first to be considered. Wound infection. A very common method o~^~-^^ „. ,« . __ I OIL CAT FIG. 115. — Powder gun with attachments. (Leggett.) 2^2 Minnesota Plant Diseases. \j cially for spraying high shade trees, stationary engines have been used. In the application of powders, apparatus is also necessary. Blow guns, pepper shakers and powder guns of various kinds are in use. Figure 115 shows a powder gun in very common use, together with various accessories and attachments. Machines have recently been devised for the treatment of oats and other grains against smuts. Such machines aim to completely immerse the grains in the solution and to keep them agitated so that all parts of the grain surface are reached by the fungicide. The above pretends to be only a general and elementary exposition of the general types of machinery in use at the present time. For further information and detail the reader is referred to the Minnesota State Entomologist's Report for 1904 and to other Agricultural Experiment Station literature. PART II.— SPECIAL. Chapter XVI. Diseases of Timber and Shade Trees — Timber Rots. Jff Wound parasites and timber rots. Features of these sub- jects have been treated of in former chapters and little remains to be said here. These fungi include chiefly members of the palisade basidium-bearing groups, as pore and gill fungi. They are capable of attacking woody tissues, feeding upon them, and converting them into the crumbling, friable mass, known as punk. Many of these forms are entirely saprophytic and occur only on fallen logs, cut timbers or standing stumps and are sim- ply timber rots. Others, ho\vever, are half saprophytes and are capable of attacking the living tissues of the stem or root. Such usually gain entrance through the bark, by means of wounds in the latter and, after a more or less short saprophytic life, penetrate outward to the living parts of the stem or roots and there attack the growing zone and inner bark. The ulti- mate result of this parasitic life is usually the death of the tree, after which the fungus continues to live on in a truly sapro- phytic manner. To the living forest trees, therefore, this class of fungi is a constant menace, and to the fallen trunks and broken trees almost a certain evil. The danger does not even stop here, for many of these forms attack stored timbers, and lumber, especially, if the latter is improperly kept. They even invade the standing and foundation timbers of houses. Some of the most serious problems in the construction of wooden houses lie in the prevention of subsequent rotting. The so-called dry rots are particularly harmful in this respect and are frequently found in their fruiting stages in damp cellars. Thorough seasoning is the only efficient remedy against such diseases. Application of creosote to the ends of joists and other timbers has also been recommended. Large timbers are often bored through lengthwise and ventilating holes bored at both ends at right angles to the long holes to allow of circulation of 236 Minnesota Plant Diseases. Minnesota Plant Diseases. 237 air to prevent dry rot. Other accessory cautions are also ad- visable and will be mentioned in the discussion of the true dry rot of timbers. Timbers in mines, tunnels and railroad ties suf- fer especially severe depredations from fungi of this class. Prevention. As to the prevention of the ravages of wound parasites of this group, an avoidance of wounds is first of all advisable. Of course this is impossible in forest culture but in shade trees it is practicable. Where trees are pruned the cut surfaces should be carefully covered with creosote or some simi- lar substance to prevent the entrance of spores and their germi- nation. Fall and winter are preferable for this pruning since the absorption of the creosote is more complete at that time than in the spring or summer and the exclusion of the fungus threads is therefore more complete. In the second place the fruiting bodies of all disease-causing fungi should be removed as soon as discovered and burned immediately to destroy all of the spores. This is a prevention against the further spread of the disease. Badly infected trees should in most cases also be removed and thoroughly seasoned or used for firewood. \Yhere the fungus is a root parasite traveling from root to root, as is known to be the case in a few forms, a trench is dug around the infected trees and all roots severed so as to prevent the spread to other trees. The isolated trees are carefully watched and the fruiting bodies destroyed as soon as they ap- pear. Many valuable shade trees are annually lost as a direct or indirect result of timber diseases and such a loss can be almost entirely averted by careful attention as indicated above. In forest culture dead trees should be immediatly cut and harvested. This saves the available timber and gives it no chance for deterioration which is sure to set in if the timber is left standing. Such treatment also prevents the formation of fun- gus fruiting bodies, which would spread disease to standing trees. There is an age at which trees may be said to become mature and at this age the natural forces of recuperation just balance the external destructive influences. This age varies in different trees. At this time the tree should be harvested, for in every succeeding year the chances of destruction by fungus pests increase and the tree loses in value. 238 Minnesota Plant Diseases. The subject of timber rots has in recent years been made the object of special study by agents of the U. S. Department of Agriculture. The following abbreviated account is based largely on these reports. The importance of timber rots can be realized in the consideration of the ties, fence posts, telegraph and telephone poles, mine and ship timbers, paving blocks and bridge timber which are all subject to conditions extremely fa- vorable for decay, in addition to all other building timbers which, though not under such unfavorable conditions, may still undergo serious rotting. Efforts have been made at different times for more than a hundred years to lengthen the "life" of such timbers by various kinds of treatments. From the nature of the case, long periods of time are necessary for carrying on experiments in this line and a great deal of progress has not yet been made. A number of satisfactory methods, however, are known at present, but on account of the cheapness of timber in this country have not until recently been introduced and are not even yet extensively employed. In the first place seasoning of timber is an important factor. Green timber contains more moisture, which is directly favora- ble to the fungus growth and subsequent decay of the wood. It must also be noted that different kinds of timber require different lengths of time for seasoning. Beyond a certain point seasoning does no good but may work harm. Even wood of the same kind from different localities may require different treatments. Seasoning, therefore, is not only an important fea- ture but is also one which is not altogether simple. Its value is beyond doubt, as has been shown by numerous experimental results. Another feature which needs mention at this point is the storage of the timbers. Close piling often results in closed moisture-laden chambers, which easily encourage the growth of fungi and the close contact of the wood admits of the rapid spread of the decay from piece to piece. The drainage of water is also seriously interfered with. Timbers, therefore, should be piled so as to admit of as complete aeration as possi- ble, so that each piece shall have the opportunity of thorough drying out in proper season. The dangers of the storage of contaminated timbers with sound timber have already been mentioned. Minnesota Plant Diseases. 239 The various methods of treatment of timber to prolong its usefulness consist entirely of impregnation processes. By these, chemical compounds in solution or emulsion are forced into the timbers or boiled in, so that they permeate the whole timber or at least the surface portions. These substances must be fungicides and antiseptic as well. They must prevent the germination or growth of the fungi or bacteria and thus pre- vent rotting. It is not always necessary that they penetrate to the center of the timber, since the surface portions, if properly impregnated, will keep out all decay-forming organisms. Of course such a substance which would penetrate to the very cen- ter would be of great advantage in the resistance towards the leaching-out process. It must be kept in mind that many com- mon fungicides are soluble in water and hence would leach out under heavy rains. This is an important factor in the impreg- nation of timber. A substance must also be selected which can be injected with ease into woods. In the case of soluble salts, the easier the injection the easier the leaching out. However, in view of the cost this is an important factor. It will not be many years when the price of timber will be such as to compel the adoption of some methods of treatment for many timbers and such is already the condition in European countries. It is rapidly becoming imperative in certain classes of timber at present and particularly those mentioned above as most liable to decay, e. g., ties, poles, etc. At present, however, the cost of impregnation is one of the first factors for consideration and often of paramount interest. The following substances have been used with considera- ble success. Creosote is sometimes forced hot into timbers placed in tanks from which the air has largely been re- moved. By this method a penetration of several inches may be effected. This process has been described as the most effective known, though on account of the considerable ex- pense of the creosote is not generally applicable. A cheaper but less effective method is that of the use of zinc chloride. This has been more extensively used. Another process is known as the Hasselman treatment. In this the timbers are boiled in a solution of the sulphates of copper, iron and alu- minum and a small amount of kainit for several hours. By this 240 Minnesota Plant Diseases, means the wood is thoroughly impregnated and the salts de- posited, not only in the cavities, as with most other substances, but also in the walls of the cells. This process has not yet been thoroughly tested but has apparently many excellent features which may perhaps, in the future, make it a valuable treatment. Other processes, either new or imperfectly known, may merely be mentioned here. In one electricity is utilized and is passed through the timber in a solution of magnesium sulphate. Two things are claimed for this treatment: cheapness and a com- plete distribution of the impregnating salt. Another method is directed toward a saving of expense in the pure creosote meth- od by using an emulsion of the oil in resin and a strong solution of soda lye. This has again been modified by the substitution of formalin in the place of the lye. The following list of timber rots and timber-tree diseases is by no means complete for the wound parasites and timber rots of Minnesota ; but it includes many common forms and above all is intended to give the reader an idea of the kind of organ- isms responsible for the rots of timbers and the deaths of timber trees. Other related forms will be readily recognized by their general similarities with these forms. The general preventive methods have been mentioned above. Only in special cases are additional measures given. Stereum wood rot (Stereum species). On the dead trunks of many of our broad-leaved trees, can often be found numerous shelf-like fungi projecting in the manner of the pored shelves. In some species the upper surface is rough, hairy or silky, and the under surface is smooth. The latter does not contain pores as in the true , pore-fungi. The shelves are usually of a leathery consistency and in dry weather often curl up, expanding again in wet weather. The spores are borne on typical basidia in pal- isades which cover the under surface. In some cases, instead of shelf-like bodies, prostrate, crust-like objects are formed which are sometimes turned back at the margins. In these cases the spores are found on the upper surface of the prostrate body. There are several species of this genus which are de- structive parasites of pur forest trees. Oaks are very often at- tacked. The fungus usually gains entrance through wounds and grows outward from that point. Fig. 117 shows an oak Minnesota Plant Diseases. 241 tree attacked by a Stereum. The progress of the mycelium up- ward in the stem is indicated by the size of the fruiting bodies, which are largest in the neighbor- h o o d of the wound and dimm- ish gradually away from the wound. Oak attacked by Stereum hir- sutum Fr. is known as white- piped or yellow- piped oak. The wood becomes brownish at first. Longitudinal white or yellow streaks then arise where, under the influence of the fungus mycelium, the wood loses its woody charac- ter. The whole block then grad- ually undergoes further decompo- sition. In a cross section of the wood these streaks are seen as whitish specks which have given the name of "fly FIG. 117.— A Stereum wound parasite (a species of Stereum). The fungus obtained entrance in the wound at the base of the tree (an oak), and, as shown by the fungus fruit- ing bodies, is gradually progressing upward. This tree died about a year after the photograph was taken. Original. 16 woo d wood tacked. to s o the at- 242 Minnesota Plant Diseases. Partridge wood rot (Stereum frustulosum Fr.}. This is a very characteristic rot of woods and is not uncommon in Min- nesota. It attacks chiefly oak and may live either as a wound parasite or in a saprophytic manner on felled timber. The fruiting bodies are hard and crust-like, light-brown to greyish FIG. 118.— Partridge wood rot. 1. The fungus (Stereum frus- tulosum), fruiting bodies on decaying wood. 2. The cut surface of the decaying wood showing the characteristic holes caused by the action of the fungus mycelium. At the edge are seen a few fruit- ing bodies in section. 3. A thin strip of decayed wood showing holes as in 2. 4. Decayed wood seen from the end of the block. Original. masses, and are found in dense clusters. They are usually polygonal, often five-sided, and grow from year to year, so that a section through the fruiting body exhibits a layered structure. On the upper side of the fruiting body, the spores are borne on Minnesota Plant Diseases. 243 basidia in a palisade layer similar to that of the Stereum wood rot. The fruiting bodies are very easily recognized, but the rot- ting wood is even more characteristic. In the early stages of rot there are seen whitish, circular or oval patches in the wood, which are more or less permeated with the mycelium of the fun- gus. In these patches the wood is quickly disintegrated while the wood dividing the patches remains very hard. In later stages the whitish patches become hollow by the complete de- struction of the wood and a longitudinal section of such a timber would show a net-like arrangement of wood enclosing the de- cayed patches. Around these holes can be seen a lining of the whitish mycelium. Finally the walls between the holes also disintegrate and the entire timber crumbles. The smothering fungus of seedlings (TJiclcphora terrestris Ehrh. and T. laciniatum Pcrs.}. One often finds, particularly in damp situations at the bases of young saplings of hard maples and other trees, blackish, soft, leathery masses forming an irregular ring around the base of the stem just above the ground. At first sight they may seem shapeless and they are not at all conspicuous objects. A close examination shows them to be composed of numerous shelves, like the shelf fungi, and usually hemispherical in shape, jutting out from the main mass of the fungus. (T. terrestris.) Another species, Thele- phora laciniatum, forms masses with irregular projections which vary from club- or tooth-shaped to fan-like in form and are usually combined into a rosette. If one examines the under surface of these shelves or clubs with a microscope one finds there numerous dark-colored spores with very rough outer walls. These spores are produced in fours on basidia which occur in palisades in the way usual for the palisade fungi. These fungi are not truly parasitic but derive their nourish- ment from matter in the soil. They have nevertheless been reported as dangerous to forest culture on account of their be- havior toward seedlings. The fruiting body starts as a shape- less mass lying on the ground and when it comes in contact with any upright support it grows upward a short distance and then produces the projections of the mature form described above. If this support happens to be a seedling the latter may become completely engulfed and destroyed. As this fungus is 244 Minnesota Plant Diseases. not very abundant in Minnesota it seems doubtful that any con- siderable damage results from it. The fungus fruiting bodies should be removed and destroyed. (Fig. 82.) Club fungus rots (Species of Clavarid). There are many species of club fungi which occur on woods of various kinds in Minnesota. These fungi, however, seem to prefer those logs already in advanced stages of decay, or they may be found on the ground where wood debris is abundant. They less fre- quently occur on solid logs or timbers. They are not, there- fore, usually counted in with the dangerous timber rots of our state. (Figs. 10, 81, 83.) The coral fungus rot (Hydnum coralloides Scop.). This fun- gus is very abundant in the hard woods of our state. The fruit- ing bodies occur on the under sides of fallen logs, in hollow logs or less frequently on standing trees. They vary greatly in size. The smallest are seldom smaller than a man's hand, while the largest would fill an ordinary water pail. The fruiting body is pure white or very slightly tinged with yellow and is very much branched. From the branches arise small teeth about one-half inch in length, which are found chiefly on the under side of the branches and hang down. The whole mass is not unlike a delicate cluster of coral growths. These fruiting bodies are higly prized by mushroom eaters as choice delicacies. The mycelium, of course, lives in the wood where it causes de- cay of the wood tissues. The spore-bearing basidia line the whole surface of the teeth and the spores are white. The fun- gus is not important as a timber rot. Closely related to the coral fungus are two other toothed fungi which are also found on wood under conditions similar to those of the coral fungus. The bears-head fungus differs chiefly in the possession of larger teeth and coarser texture. The medusa-head fungus produces fruiting bodies more yel- lowish in color and the teeth are very much longer, often attain- ing" a length of several inches. The teeth are usually densely packed together and the whole fruiting body presents a more nearly solid mass than either of the preceding forms. It is found on forest logs and stumps and specimens have been re- ported on building timbers in cellars. (Figs. 81, 84, 119.) Minnesota Plant Diseases. 245 Dry rot or house fungus rot [Merulius lacrymans (IVulf.) Schum.]. This fungus is one of the most destructive of timber rots both on ac- count of its action and its frequent oc- currence. It is one of the simplest of the pore fungi, hav- ing only shallow pores on a flat pros- trate fruiting body. It may almost be termed a domesti- cated fungus for it appears almost ex- clusively in the neighborhood of dwellings and is very seldom seen native in the woods. It has therefore been called by the Ger- m a n s "h a u s- schwamm" or house fungus. It is also popularly known as the weeping fungus. It attacks chiefly the 1 FIG. 120. — The fruiting body of the dry-rot fungus (Merulius lacrymans). The under surface covered with shallow pores is shown in the photograph. Much reduced. Original. soft woods of needle trees but may also destroy oak and other hard woods. This fungus is a typical saprophyte and de- rives its nourishment from the wood which it destroys. When the mycelium has permeated a wood tissue it leaves the latter as a spongy mass of brownish material, a common condition in timbers which are kept in moist places. Such decayed wood absorbs water readily and retains it so that the wood holds its original size and shape, but when dry the decayed portions shrink, causing cracks which form at right angles to each other, 246 Minnesota Plant Diseases. Minnesota Plant Diseases. 247 commonly forming squares. Wood so affected is very friable and can be easily rubbed to a powder. Water passes easily through such decayed parts and further aids in the invasion of new portions and of other timbers in contact with it. In moist, dingy cellars, where the atmosphere is always more or less damp, and the timbers never have a chance to thoroughly dry out, the fungus develops a vigorous, superficial mycelium, which appears at first as a fine, thin, woolly coat of pure white threads. This soon grows into a dense sheet of white felt which can easily be peeled from the wood. In this sh'eet there develop later thick strands composed of threads which are packed with nutrient material. These strands are of great im- portance as they often grow to great lengths and may carry in- fection to timbers distantly located. Walls of stone or earth offer no obstacles to such progress, since the fungus strands are provided with a great amount of nutrient material. When they finally again enter the wood they establish a mycelium which supports itself upon the wood tissues. The fungus is also remarkable on account of its ability to attack almost perfectly dry wood. It can absorb sufficient moisture from the air to keep it from drying up and may thus slowly destroy the wood. The excess of moisture absorbed by wood attacked by this mycelium often condenses out into drops on the infected parts and has given rise to the common name of "weeping pore fungus." The fruiting bodies are flat and prostrate and never form shelves. At first they are white, then reddish and later turn dark yellow brown on account of the numerous spores pro- duced on the surface. Wrinkles and folds form on the surface of the fruiting body and shallow pores are thus produced. The spores are dark yellow-brown and very small. It has been esti- mated that 65,000 millions could be crowded into a space of one cubic inch. The fruiting bodies are often five or six inches in diameter. In one end of the spore wall is a thin place through \vhich the germ tube emerges when germination takes place. This pore is closed with a small plug and it has been claimed that this plug is removed only in the presence of alka- line material, as wood ashes, coal dust and humus materials. After the removal of the plug the germination can proceed as 248 Minnesota Plant Diseases. , , ,;:. , •m FIG. 121.— The dry-rot fungus (Merulius lacrymans). Shows the surface of a pine board which has been attacked by the dry-rot mycelium; it is not yet, however, com- pletely converted to punk. The felted mycelium has been partially removed show- ing the accentuated grain of the attacked portions. The mycelium has penetrated some distance beyond the white mycelial felt. Original. Minnesota Plant Diseases. 249 tinder conditions normal to other spores. It has therefore been recommended that such substances as furnish alkaline materials be not brought unnecessarily into contact with structural tim- bers. The fruiting body has an agreeable odor when young but when old and in the stages of decay emits foul odors and in- jurious gases and an excessive amount of water may be exuded by the diseased timbers. FIG. 122. — The dry-rot fungus (Merulius lacrymans). Later decay stages than that shown in Fig. 121. From the board shown on the left, the mycelial felt has been removed and the checked portion of the board is seen. This appearance is caused by the drawing of the tissues in drying after the decay has been well started. The removed mycelial felt is shown in Fig. 5. The board shown on the right is in a still further stage of decay and the wood under the mycelium is reduced to friable punk. Original. As has already been stated, infection of timbers does not usually take place in the forest. It may occur where old timber is stored with fresh lumber or where old timber is used in the building of a new house. Workmen may carry spores on their clothing or tools and thus cause an infection of timbers. The 250 Minnesota Plant Diseases, evils of green lumber are here apparent, for infection takes place more readily than in well-seasoned material. The preventive measures are indicated in the above ac- count. The' fruiting bodies should be destroyed as soon as they appear. Well-seasoned wood is preferable to green wood. The use of partially diseased wood is dangerous on account of the probable spread of the disease to other timbers as well as to the healthy parts of the diseased timber. Moist deadening material of all kinds should be avoided as also such substances which could create alkaline solutions in the presence of mois- ture. Ventilation of large timbers is sometimes effected by boring longitudinal holes through the center and transverse connecting holes near the ends. In general, the formation of stagnant, moisture-holding cavities should be avoided wherever possible. (See also Fig. 5.) The false tinder-fungus rot[Fomes igniarius (L.) Fr.]. This is one of the true pore fungi and is a dangerous and common timber parasite. The plant gains entrance to the living stem through the bark, usually at a wound or other opening which may have been caused by such agencies as wind, hail, squirrels, birds or boring insects. When the fungus has gained entrance it attacks the growing portion of the stem, which is situated just beneath the bark and it may establish here an extensive mycelium. From this mycelium are later produced the shelf- like fruiting bodies. The latter are usually half globular when young, becoming hoof-shaped when older. The lower surface is lined with a layer of pores which are white when young, be- coming dark yellow-brown with age. New layers are added in successive seasons. The upper surface of the fruiting body has usually a very hard coat. Internally it consists of a softer brownish felt-like material and numerous long tubes, which end at the lower surface. The hard skin of the upper surface of the fruiting body is usually cracked in older specimens. The wood attacked by this mycelium undergoes a white rot. It first be- comes dark in color, then as the process of disintegration con- tinues it becomes yellowish to white. The fungus threads at- tack the walls of the wood elements destroying their woody characters and leaving them softer and lighter in color. The chief danger of this fungus lies in the destructive parasitic habit Minnesota Plant Diseases. 251 for whole forests have been reported killed by it. It is not uncommon in this state, particularly on oaks. Tinder-fungus rot [Fames fomcntarius (L.) Fr.]. This fun- gus is similar in its habits and characters to Pomes igniarius. Like the latter it is a true pore fungus. The pores on the lower surface are at first whitish, becoming grey-brown with age. New7 layers of pores are laid on each year as can be seen by the zoned character of the shelf. The upper surface of the fruiting body becomes covered with a very hard coat of greyish color. Internally the fruiting body consists of a felted, softer material above and a tinder mass, through which the long pores, built up in zones, extend to the openings on the lower surface. The age of the fungus can be approximately figured from the num- ber of zones in the fruiting body. It may be of considerable age and of such a size as to be useful for tinder. Specimens have been observed which were almost a century old. The tinder fungus is, like the false tinder-fungus, a danger- ous parasite and gains entrance through the stem in a similar manner. The growing zone beneath the bark, chiefly upward and downward from the point of entrance, is killed and the wood beneath undergoes rotting. Wood attacked by the tinder fungus becomes yellowish. Radial patches of the white felted mycelium may often occur in such wood. The fruiting bodies of the tinder fungus were formerly ex- tensively used in Europe for tinder and also in the manufacture of caps, gloves, etc. The tinder has also the property of staunching blood-flow from cuts and has been used for that purpose. The flattened pore-fungus rot [Ponies applanatus (P.) Wallr.~\. This is a very common pore fungus on old stumps and fallen logs, less commonly found growing from wounds on living trees. The hard-crusted shelves vary greatly in size, some of the largest attaining a width of several feet. The shelf is woody and the upper surface greyish to brown. The latter is often covered with a fine dust of accessory spores of a dark reddish brown color. The upper surface is covered with a hard crust and the interior of the shelf is of a softer fibrous texture and dark brown in color. The pores are very small and cover the under surface, which is pure white, when newly formed. 252 Minnesota Plant Diseases. The fruiting body lives from year to year, adding new growths of pores annually. The sulphur-fungus rot [Polyporus sulphur eus (Bull.} Fr.]. After a prolonged rainy season in spring or summer one often FIG. 123. — The fruiting body of the flattened pore-fungus (Fomes applanatus) ; on a standing dead tree trunk. Original. finds, particularly on oak trees, large masses of a tough, fleshy fungus, consisting of numerous shelves overlapping each other. The shelves are yellow to bright red above, becoming yellowish- white with age ; the lower surface of each shelf, where the pores occur, is of a pure sulphur-yellow color from which the common Minnesota Plant Diseases. 253 name of the fungus is derived. In the young stages the fruiting bodies are somewhat soft, fleshy or cheesy and are often eaten by mushroom hunters. When older and especially under dryer conditions, they become tougher in consistency and paler in color. Very old masses are often found to be badly worm- eaten and much of the fruiting body is reduced to a powder. The fruiting bodies do not persist from one season to another but go to pieces each year. New crops are produced yearly. FIG. 124. — Fruiting bodies of the sulphur pore fungus (Polyporus sulphurous); on a dead oak stump. Original. The fungus is a common wound parasite. The wood, when attacked, becomes brownish red and dries out rapidly. Slits and cracks soon arise in the wood and these become filled with dense masses of the thickly felted mycelium. The wood in the last stages becomes brittle and the entire tree usually succumbs to the attack of the fungus. Oaks in our state appear to suffer considerably from the sulphur fungus but other deciduous trees and some of the conifers may also be attacked. 254 Minnesota Plant Diseases. The scaly pore-fungus rot [Poly poms squamosus (Huds.) Fr.~\. This is a very common pore fungus which causes a white rot of timbers. It occurs abundantly in spring, forming large shelves, usually in groups. The fruiting bodies are soft and fleshy at first and their upper surface is conspicuously marked with dark brown or blackish scaly patches (squamae). It is attached, usu- ally by a short stalk, which is almost always found on the edge of the fruiting body. As the latter gets older it loses its fleshi- ness and becomes harder, dying the same season, so that a new FIG. 125. — Fruiting body of the scaly pore fungus CPolyporus squamosus), seen from both surfaces. After Loyd. crop of fruiting bodies must be formed again the following year. The pores are very large, somewhat shallow and angular and often run down some distance along the stalk. This fungus is usually found on dead logs or stumps but may also grow on dead parts of living trees. The birch-fungus rot (Polyporus bctulimis Fr.} This birch fungus is perhaps the most common of our pore fungi. In al- most every clump of birches its fruiting bodies may be found. Minnesota Plant Diseases. 255 The latter are annual and have a very characteristic and beau- tiful appearance. They are hemispherical in shape and the short stalk is always attached to the side. The upper surface is grey to light brown in color, is very smooth and covered by a thin skin. The pores on the under surface are small and rather deep and the layer in which they are found is easily separable from the rest of the fruiting bodies. The flesh of the fruiting body is pure white and somewhat spongy in texture. In old dried fruiting bodies the flesh is very commonly found to be honey-combed by the larvae of insects. FIG. 126. — Fruiting body of the birch pore fungus (Polyporus betulinus), on a branch of a white birch. Original. The parasitic relationships of this fungus with the birch trees have been established by several investigators and there is little doubt that the fungus causes the death of many birches in this state. The fruiting bodies are usually found on dead birches, often accompanied by other pore fungi. The mycelium in the living tree grows not only through the growing region of the stem and the inner bark but also attacks the wood. When the mycelium which may be growing for years has accumulated sufficient food material a fruiting body is formed. A new crop is produced every year, if conditions are favorable. 256 Minnesota Plant Diseases. Trametes root-rot (Tramctes radiciperda Hartig.). This root-inhabiting pore fungus has been very thoroughly investi- gated in Europe where it has done an enormous amount of damage to coniferous and broad-leaved forest trees. The myce- lium of the fungus travels from root to root in the living trees and the disease is thereby rapidly spread. It later passes from the root into the stem, chiefly through the inner bark, and here attacks the wood. The affected trees soon die and the wood undergoes a red rot. The fruiting bodies are formed where they may distribute their spores into the air and are therefore usually above ground. They are irregular in shape varying ac- cording to their position; they are brown above, have white flesh, and the lower surface, upon which the pores are formed, is also white. The fungus is not infrequently found on timber in mines. European botanists recommend for the prevention of the spread of this disease the isolation of the infected region by dig- ging ditches deep enough to cut through all of the roots, there- by preventing the spread of the mycelium by way of the roots. In the isolated areas, fruiting bodies may develop either from the exposed roots or from the standing trunks. To prevent the spread of the disease by means of the spores so formed, the roots should again be covered with soil and the trunks and stumps burned. The formation of mature fruiting bodies should be prevented. The extent of the distribution of the fun- gus in Minnesota is as yet unknown. Ring scale of pine [Trametes pini (Brot.) Fr.]. Ring scale is a very common parasite on pines both in Europe and in this country ; it is also known on Douglass fir. The fungus gains en- trance to the tree usually through wounds or broken limbs, par- ticularly the older branches, in the heart-wood of which no pro- tection-coat of resin has been formed. After it has gained en- trance to the stem, the mycelium grows in longitudinal stripes above and below the points of entrance; in the same year's growth and in successive years it works from the interior to the exterior. In this way zones of the diseased regions are formed exteriorly (ring scale). The wood attacked by the ring scale un- dergoes a peculiar disintegration. There are formed in the de- caying wood numerous small, isolated patches of the white my- Minnesota Plant Diseases. 257 celium of the fungus. These differ from the similar patches in the Trametes root-rot in the usual absence of black centers. The fruiting body is brown and either forms a shelf or is diffused into a coating over the bark. It is woody and perennial, producing new pore areas successively for many years. The pore area is on the lower surface of the shelf forms and on the outer surface of the prostrate fruiting bodies. The oak Daedalea \Dce- dalca qnercina (L.) PersJ], The cause of this disease is a pore fungus and is not un- common on the dead trunks of oaks ; it is one of the most common rots of oak railroad ties. The fruiting body is a thick shelf, woody in ap- pearance but in consistency tough-corky. It is pale buff in color and the upper sur- face is smooth, though usu- ally more or less zoned and sometimes ridged. The pore surface is often half- cone-shaped and the pores are elongated from the cen- ter toward the edge. The pores are more or less sinu- ous or wavy in outline and are especially elongated to- ward the point of attach- ment. The pore surface is of the same color as the top of the shelf. ,8 258 Minnesota Plant Diseases. The parchment pore-fungus rot (Polystictus pergamenus Fr.\ This is an exceedingly abundant pore fungus found on various kinds of soft wood trees. It is very common on birch, where one frequently finds whole logs covered with the densely crowded fungus shelves. Occasionally one finds the fungus on the living trees. It has also been observed on living larch trees where it occurs in great abundance. The fruiting body is a thin, reflexed shelf which is very light tan colored above and covered with dense hairs. The pores are found on the lower surface and are shallow at the edge, increasing in depth toward the center. They are often of a purplish or violet tinge and the pore walls become, with age, so badly torn that the under surface of the shelf has the appearance of a toothed or hedge- hog fungus. There is strong evidence that it has caused the death of numerous larch trees in Minnesota. (Fig. 36.) Wood-rot of the creeping pore-fungus [Polyporus vapora- rius (P.) Fr.]. This fungus is reported as very abundant in Eu- rope and forms very similar to it are known in Minnesota. A description of this fungus will therefore not be out of place since it is not improbable that it exists in the state. The fun- gus attacks chiefly soft coniferous woods and is a wound para- site. It is found in the roots and on the stem and is a danger- ous enemy to trees. The mycelium develops in cracks and un- der the bark, forming a dense, white felt and causing rapid de- cay of the wood. The fruiting bodies are white, flat, prostrate forms and do not produce shelves. The pores are small and cover the upper surface of the fruiting body and are very numerous. The mycelial felts and strands are not unlike those of dry rot and the disease is often confused with that of true dry rot. It is frequently found in the timbers of dwellings where it is a dangerous agent of decay very similar in its action to that of the dry rot fungus. The zoned Polyporus rot [Polystictus versicolor (L.) Fr.~\. This is one of our commonest of pore fungi, found chiefly on old stumps and decayed timbers. The shelves are thin and leathery and conspicuously zoned above. The zones are of dif- ferent colors varying from light tans to very dark brown or black and are frequently velvety in appearance. The pores are on the under surface and are very small. They are white at the Minnesota Plant Diseases. 259 surface when fresh. The pore walls often become torn with age. The shelves vary somewhat in size; they are generally from two to three inches across and are aggregated together into very dense clusters in shingle fashion. They appear usual- ly when the logs or branches upon which they form are in ad- vanced stages of decay. The zoned pore fungus is perhaps not of great importance as a timber rot, though it is very frequent on railroad ties. The pitch-stemmed pore-fungus rot (Poly poms picipes Fr.). This form of pore fungus' is conspicuous in our woods on account of its large, thin fruiting bodies which are attached by a short black stem. It occurs on broad-leaved trees and is usually found on decaying logs or stumps. It has been reported as occurring on living trees but little is known of its relationship with the latter. Though not uncommon, especially in hard maple and basswood forests, it is not usually very abundant. The fruiting bodies are thin and tough, leathery when moist, becoming brittle when dry. They are usually broad-beaker-shaped to flattened when mature, are dark red-brown above and have a short central black stem. The fruiting bodies are not at all fleshy. The lower surface, which contains the very minute pores, is dirty yellow in color. The hairy pore-fungus rot(Polystictus hirsutus Fr.). This is a very common shelf-pore form which occurs abundantly on dead sticks and limbs of trees. It has been reported also on living trees of hornbeam, alder, birch and oak but exact details of its relationships with these plants are wanting. Chapter XVII. Diseases of Timber and Shade Trees, Timber Rots {Continued}. Jff The shoe-string fungus rot [Agaricus (Armillarid) mellcns Bahl.]. This fungus is also known as the honey-colored mush- room. It is undoubtedly the most common of all of our fall mushrooms. Its edible fruiting bodies may be found at the base of almost any of our indigenous trees. They are very frequent at the base of dead stumps, but may also occur on the ground. They are usually found in dense clusters the lower of which are covered with the fallen spore-powder from the up- per fruiting bodies. The whole fruiting body, except the gills, is more or less honey-colored — hence its common name. The stalk is usually swollen toward the base and carries near its sum- mit a membranous remnant, the so-called annulus. The annu- lus is usually conspicuous especially in the younger stage, but is sometimes only slightly developed and occasionally entirely wanting. The mushroom cap is lined on the under surface with plates or gills which radiate out from the stem and bear the spores. These are wrhite and may often be found as a fine white powder covering sticks and leaves under the fruiting bodies. The honey-colored upper surface of the latter is covered with fine, fibrillar scales of a darker color. These scales may also be found on the young stem. When old the whole fruiting body may become entirely smooth. At the base of the stipe may usually be found a shoe-string- like strand of the mycelium from which the fruiting body orig- inates. These strands which resemble small, leather shoe- , strings in appearance run long distances through the earth and also occur just underneath the bark of trees where they are usually somewhat flattened. The mycelium of the honey mushroom may be parasitic on trees and is one of the most de- structive of timber diseases. When the strand of a mycelium Minnesota Plant Diseases. 261 262 Minnesota Plant Diseases. comes into contact with the living root of a tree it bores its way through the outer bark into the soft bark and the growing re- gion ; here it frays out into a fine felt-like expansion and attacks the living cells. The latter are killed and the fungus proceeds between bark and wood up to the stem and often for some dis- tance up the latter. From the stem the mycelium may make its way down into healthy roots. The attack on the root sys- tem results in the death of the tree by cutting off the supply of crude materials. At the base of such a trunk one may later in the autumn find the fruiting bodies. The mycelium in the trunk and roots assumes the form of shoe-string strands and these may grow into a very well developed net-work just under the bark. The mycelium may continue to live on the timber saprophytically after the death of the tree. This fungus has often been reported as a timber-destroying fungus in mines. The honey-colored mushroom attacks the oaks and probably other broad-leaved trees in our state. In Europe it has been reported as particularly destructive to coniferous woods, as well as to broad-leaved trees. When the disease becomes epidemic, no successful combat- ive measures are known. All diseased trees and fruiting bodies should be burned and young trees should not be planted on in- fected areas. (See also Figs. 6, 7.) The fatty Pholiota rot (Pholiota adiposa Fr.). On standing trees and particularly on felled timber of oaks and other broad- leaved trees, one often finds in fall clusters of a conspicuous, bright-yellow mushroom, which is responsible for a white rot of timbers. The fruiting bodies may be six inches or more in length ; the cap is bright yellow with concentric, blackish spots. The latter are also found on the stem, which is about of equal diameter throughout its length and is tough-fleshy. The cap m moist weather is covered with a slimy gelatinous coat. On the under surface of the fruiting body are gills radiating from the stem as in the honey-colored mushroom. These gills are in this case, however, yellowish to grey in color and throw off ochre- brown spores, which, often discolor the stem or other objects upon which they fall. The mycelium attacks the wood and forms bands of white felt which separate the wood up along the lines of the annual rings. Although not infrequently met Minnesota Plant Diseases. 263 with, this parasite is probably not very destructive to timbers in this state. It has been observed on living shade trees. FIG. 129.— Fruiting bodies of the fatty Pholiota (Pholiota adiposa), in a wound of an oak tree trunk. Original. The scurfy Pholiota rot (Pholiota sqnarrosd Mull.). This is a close relative of the fatty Pholiota and forms fruiting bodies which resemble those of the latter. They are not so viscid in rainy weather and are persistently scurfy. It occurs on logs, 264 Minnesota Plant Diseases. Minnesota Plant Diseases. 26 - stumps and cut timber in a manner similar to the preceding species. The velvet-stemmed Collybia rot (Collybia velutipes Curt.). This is an exceedingly abundant fungus especially on cut tim- ber and standing stumps or fallen logs. The fruiting bodies are of the gill-fungus type and usually occur in clusters. The upper surface of the cap is yellowish to tawny and in wet weather is viscid. The gills are light yellow to tawny and produce white spores. The stem is covered with a velvet-like coat of a dark brown to blackish color, especially toward the base of the stem. The fruiting bodies are about one to three inches in length and FIG. 131. — Fruiting bodies of the sapid Pleurotus (Pleurott:s sapidus), on a standing yellow- birch trunk. Original. the cap about one to two inches across. They may be found at almost all seasons from early spring to late fall. This fungus causes one of the rots of timbers and is usually a saprophyte. It has been observed on living elm trees, however, and is possi- bly a wound-parasite. The elm Pleurotus rot (Pleurotus ulmarius Bull.}. This very common gill-fungus is usually found on elms and maple trees, growing from dead trunks or from wounds in the living trees. 266 Minnesota Plant Diseases. A parasitic life has not been demonstrated for it, but its pres- ence in the wood of living trees is known. It is frequently found on shade trees, especially on trunks, which have been pruned and not subsequently protected. The fruiting body is pure white and usually large, often at- taining a length of six or seven inches and an equal cap width. It is usually fleshy and the stem is slightly removed from the center of the cap (eccentric). The spores are pure white. The fruiting bodies are frequently clustered. This is a popular edi- ble fungus. Several other close- ly related forms are likewise saprophytes on timbers. Of these the oyster fungus (Pleuro- tus ostreatus) and the sapid fungus (Pleuro- tus sapidus) are best known and very com- mon forms. They are all three prized as edi- ble mushrooms. (See also frontispiece and Fig. 20.) The pine Lenzites [Lenzites abietina (Bull.} Fr.]. This is an exceedingly common timber rot on soft woods. It occurs on railroad ties, fence rails and posts and on 3 >, II be o C 3 •£ a '' Minnesota Plant Diseases. 267 soft wood timbers wherever they are .placed in conditions favor- able to the fungus. The fruiting body is either a flat prostrate one or may become a low shelf. It is seldom large and does not usually exceed a few inches in diameter. The exposed sur- face is covered with gills which often radiate from the center in the prostrate forms. The fruiting bodies are tough-leathery to woody and dark-yellow- to red-brown in color. The top of the cap is somewhat hairy when young, becoming more or less smooth when old. The gills are rather thick. The scaly Lentinus rot (Lcntinus lepideus Fr.). This is a very familiar gill fungus which inhabits almost all kinds of soft needle-leaved tree timbers. It is, as far as is known at present, a saprophyte. It is very frequently met with on fence rails and posts, dead and down tamarack and other kinds of coniferous wood, as well as on wood partially submerged in the soil or water. The fruiting body is a stalked form with a central stem and is very tough-fleshy. The cap is two to* three inches or more across and is at first pale yellow. Later, black scales de- velop on the upper surface. The flesh of the cap is white. The gills are slightly wavy, running down the stem for a short distance and the margins are irregularly toothed, — a character by which this fungus and its close relatives can readily be distin- guished from other gill fungi. The gills are white, tinged with yellow. The stem is one inch or more in length and usually ta- pers toward the base, is hard, pale in color and has scales similar to those of the cap. The fruiting bodies sometimes grow in clusters. The green cup-fungus rot [Chlorosplenium aeruginosum (Ocdcr.) DeN.]. On various kinds of woods, including bal- sam fir and birch, grows a fungus with a remarkable habit. The mycelium penetrates deeply, being especially prominent in the spring wood. It colors the wood a very beautiful, deep verdigris green, varying in shade in the different parts. It is more abundant in the summer wood, thus accentuating the grain. The rot works very slowly. Wood, so colored by artificial infection, is used in the arts in the manufacture of Tunbridge ware. It is also used for the extraction of the pigment which resides both in the mycelium and the adjacent walls. The fruit- ing body is a small stalked cup which at first sight looks much 268 Minnesota Plant Diseases, like a smooth-surfaced palisade fungus. The whole fruiting body seldom attains a length of more than three-eighths of an inch and a width of one-fourth inch. The sacs, with eight spores each, line its upper surface. The whole cup is colored similar- ly to the mycelium. This rot is particularly abundant in the northern part of the state, though on account of its slow growth and its preference for the smaller branches it does com- paratively little damage. Stem canker of balsam fir [Dasyscyplia resinaria (Cook and Phil.) RehniJ]. The cause of this disease on the common balsam-fir is a very small cup fungus. It causes canker swell- ings on the stems and branches. These cankers usually par- tially and sometimes entirely encircle the stem. In the latter case the tree trunk is killed and the balsam dies. In the canker an abundance of resin is formed. The disease is very similar to the European larch canker, which forms on the common larch of Europe a similar resinous canker. The fungus fruiting cups are produced only on the cankers and are formed within a year of the death of the infected branch or tree. The fruiting bodies are thus produced during the saprophytic life of the fun- gus. The earlier life of the fungus is probably parasitic, though no infection experiments have been carried out to prove this point. The fungus cups are very small — about one-fifth of an inch in length and of about the same width. They are provided with a very short stalk and are covered with very fine hairs. The disc or inside of the cup where the spore sacs are formed is orange-colored. The attacked portion of a branch shows a thickened inner bark and the wood rings are also increased in thickness. No remedial measures have been worked out. Tar spot of maple [Rhytisma acerinum (P.) Fr.]. One fre- quently meets with b'ack, tar-like spots on leaves of maples in late summer or early fall. These tar spots are caused by a fun- gus of the cup-fungus group and the spots are in the nature of a storage mass of threads which persist through the winter. In the early summer the spots are yellowish ; they then produce small pear-shaped depressions, containing very small spores, which flow out of the depressions onto the surface of the spot. In the fall the spot turns black and then resembles a drop of Minnesota Plant Diseases. 269 tar. In this condition it rests over until spring, when the cup fruiting-bodies are produced. Several cups spring from each spot and each cup is lined, on its inner surface, with a pal- isade of sacs containing eight spores each. Between the sacs are numerous sterile fungus threads. Spotted leaves should be collected in the fall and burned to prevent a spread of the dis- ease in the following spring. The formation of the sac spores is thereby effectively prevented. 270 Minnesota Plant Diseases. Tar spot of willow [Rhytisma salicinwn (P.) Fr.]. This dis- ease is very similar to that of the tar spot of maples. (See the latter.) The tar spots become black in August and September and may be formed in great numbers. Sometimes leaves are completely covered by the spots and are consequently seriously injured. When the disease threatens to become serious the spotted leaves should be collected and burned in fall. Ring fungus or ring disease of cone-bearing trees (Rhizina inflata QueL). This fungus is a member of the morel group of sac fungi, but might almost as well be included in the cup fun- gus group. The fruiting-body is a flattened, crust-like object of very dark brown or blackish color, fleshy in consistency and sticky in moist weather. It may attain a width of several inches and is usually irregular in shape. It is found at the base of trees or on old stumps and is commonly a saprophyte. It is attached to the soil or tree stump by numerous strands of the mycelium which run into the substratum for some distance. The sacs of the fruiting body are long cylinders and contain eight spores each. The mycelium may under favorable conditions become parasitic on the roots of trees. It grows around the root, killing the tissues, and may thus ultimately effect the death of the entire tree. It has not yet been reported from Minnesota but is known in Wisconsin and very probably exists in our state. The fruiting bodies should be destroyed. The green mold rot of timber (Species of Penicillium). There seems to be some evidence that the common green molds, which are so conspicuous as saprophytes on starchy food materials and on cheese, are capable in themselves of causing rot of timbers. Such a mold thrives on the starchy material which is stored up in the medullary rays of woody tissues and from this point invades the woody fibres. The green mold very frequently accompanies other rots and may assist in the disin- tegration of the wood. It is doubtful, however, that it is ever in itself alone a very serious cause of the decay of timbers. The ordinary mass of green mold is composed of thousands of minute, brush-like clusters of strings of green spores which are exceedingly resistant and can retain their power of germina- tion for a long time. The winter spores are formed in sacs, produced in closed capsules, which open only by irregular split- Minnesota Plant Diseases. 271 ting or by the decay of the walls. These capsules are not con- spicuous and are not met with frequently. For a more com- plete account of the life history of these fungi the reader is referred to Chapter IX. The growth of this mold is favored by close, moist conditions. Slime flux of trees. Slimy, mucilaginous material can some- times be found flowing from wounds in oak, apple, birch, elm, maple and other trees. The wound in itself may not be due to any fungus disease but may be caused by pruning, frost or sunscald, etc. In the slime which proceeds from the wound, however, one usually finds a simple form of the sac fungi (an Endomyces) closely related to the mold of the honey mush- room, and to the yeast fungi. The fungus mycelium is com- posed of branched threads, on which the simple four-spored sacs are found. There is considerable doubt that the Endo- myces is the cause of the slime flux. In the flux one may also find one or more yeasts and other fungi, bacteria and plants be- longing to the blue-green algae. Through the agency of the yeasts fermentation often sets in and the flux may then have an odor of beer. Slime-flux wounds often increase in size until large areas of bark die off and the whole tree may subsequently die. Shade and park trees are sometimes killed off in this manner. As the cause of the flux is not definitely known, methods of prevention are not understood. The usual precau- tions which are recommended for treatment when trees are pruned should be followed. Witches'-broom of birch (Species of Exoascus). Cultivated birches are sometimes attacked by this fungus. The results are seen in the production of witches'-brooms, somewhat similar to those produced in cherries. The fungus is a similar one and produces its sacs on the twigs and leaves. The infected por- tions should be cut back and burned. The Nectria of red-knot TQi\Ncctria cinnabarina (Tode) Fr.]. This fungus is not uncommon in the state. It is a wound par- asite, gaining entrance to the inner bark of the tree by such wounds as are produced by hail, birds, squirrels, storms or pruning. Infection takes place from the mycelium which grows into the bark from the wound and establishes itself in the water-conducting tissues of the wood. By continued 272 Minnesota Plant Diseases. growth the mycelium permeates the wood and then the grow- ing zone of the tree and the bark are destroyed. The fungus continues to live in the dead wood as a saprophyte and under such conditions produces its fruiting bodies. At first, small clusters of soft, bright red, button-like cushions arise. From the surface of these cushions are produced tiny summer spores, which are successively pinched off from upright threads on the surface of the cushion. These spores are capable of immediate germination and may spread the disease very rapidly. After the formation of these spores has gone on for some time, they decrease in number and finally cease to form. There then appear upon the same cushion small, red, pear-shaped to spher- ical protuberances, which contain a central cavity and a pore- like opening to the exterior. These are the sac-spore capsules. At the base of the cavity are found long, cylindrical sacs, each of which contains eight spores. The opening of the capsule is lined internally with hairs which clothe the whole canal, leading from the cavity to the exterior. The sac-spores and the sacs are extruded through this opening. The spores will germinate under favorable conditions and will again produce a mycelium in the wood. The treatment of this disease is similar to that of wound par- asites in general, i. e., burning of the infected twigs and wood and clearing up of felled wood to prevent the growth of wild spores. Leaf blister of oak (Species of Taphrina). This fungus is a relative of the fungi of plum pockets and leaf curls and of the witches'-broom fungus of cherry and birch. The spores are produced in sacs which are arranged in a dense palisade on the tinder surface of the leaf. The leaf is usually distorted in a blis- ter-like fashion, whence the common name of the disease. The red oak has been found in this state attacked by this fungus, though not to any serious extent. The removal and burning of the affected parts would be advisable to prevent a severe re- currence of the disease. Willow blight or powdery mildew [Uncinula salicis (D. C.) Wint.]. The blight of willows is an exceedingly common dis- ease not only of the willows, but also of the poplars, cotton- woods and birches. The mycelium is usually very abundant and Minnesota Plant Diseases. 273 conspicuous in late summer and forms a thick, whitish covering over the leaf. On this arise the spore-sac capsules as tiny, black, pinhead-like bodies, which often occur in great numbers. The mycelium may cover both sides of the leaf and may some- times be found on almost every leaf of the affected tree, though it is usually most abundant or entirely confined to the leaves of the lower branches. All species of willow are attacked. FIG. 134.— Powdery mildew of willow leaf (Uncinula salicis). The minute black spots are the spore-sac-capsules and under these can be seen the whitish mycelial coat of threads. Original. The sac-capsules are large compared with most other Min- nesota powdery mildews. They are black in color and have a ring of numerous, colorless, thread-appendages, each of which terminates in a single-pointed hook, in a manner similar to that of the vine powdery mildew. Each capsule contains at least several sacs, in each of which are found eight spores. The summer spores occur in the manner usual for the powdery mil- dews, producing a powdery, starchy, dust-like coating. 18 274 Minnesota Plant Diseases. Though a very common fungus, it does not very often occur in sufficient amount or at the proper season to cause very ex- tensive damage and usually no preventive methods are deemed necessary. The ordinary sprays for the fungi with superficial mycelia would probably prove effective against this disease. (See also Fig. 52.) Powdery mildew of elm$(Uncinula macrospora Peck}. This mildew is not uncommon, though it cannot be said to be abun- dant throughout the state. It attacks only the young trees or saplings of elms. On an affected tree the fungus is usually exceed- ingly abundant, covering many or most of the leaves with a very con- spicuous mildew. The latter attacks the leaves and oc- curs on the upper surface. White, circular patches of the superficial mycelium are formed and these may combine with neighboring ones to cover the entire leaf. These patches are con- spicuously white and dense and have a somewhat starchy appear- ance. The win- ter-spore fruiting FIG. 135. — Powdery mildew of elms (Uncinula macrospora), bodies are SOOre- on an elm leaf. The exceedingly minute black spots are sac-capsules of the fungus. The fungus mycelial threads SaC-CaOStlleS and form in spots which are very conspicuous. Original. Minnesota Plant Diseases. 275 appear on the mycelium as very minute dots which are at first yellowish and finally become black. Each capsule, when seen under the microscope, is surrounded by a dense circle of thread appendages which are hooked at the end in a manner similar to those of the powdery mildew of willows. Each capsule con- tains numerous sacs and each sac contains two very large spores. It is very possible that this fungus causes a considera- ble amount of damage to young elms in forests. The summer spores are formed earlier and cause the starchy appearance of the young mycelium. The fungus does not seem to be widely enough distributed to be a serious menace at present though the vigor with which it attacks is an indication that it may at some future time become a dangerous pest. Pine stem rust (Species of Peridennium). The branches and stems of pine trees are attacked by this fungus. The result- ing disease is commonly known as pine knot. The infections are more or less localized and do not extend through the whole plant. The infected portion is stimulated to the production of boil-like swellings which may continue to grow for years. The swelling is often accompanied by an abundant formation of resin and turpentine which sometimes exudes from the canker. The fungus attacks the growing zone in the stem and may finally completely encircle the latter, but this usually happens only after a struggle lasting through several years. The con- duction of the water through the stem is seriously interfered with and a drying up of the upper part of the tree may result. The fungus causing this disease is a rust fungus and is a true parasite. The complete life histories of the American pine-stem rusts have not yet been unraveled ; but from a com- parison with better known European forms it seems very prob- able that our species pass a part of their life on another host, be- side the pine. On these so-called alternate hosts the winter spores are to be looked for ; these spores are therefore at pres- ent unknown. The swellings of the pine stem described above always bear the cluster cup spores. The latter are found in cluster cups or over flat areas on the surface of the canker. They are light yellow or yellowish-orange in color. When the cluster cups open in the spring, large areas on the surface of the canker are covered with a bright yellow coat of spores which 276 Minnesota Plant Diseases. are later uncovered by the splitting off of scales of the bark. Jack pine in Minnesota is very commonly affected and the white and red pines are also though not so frequently attacked. Scotch pines in nurseries and experimental forests are some- times very seriously affected. FIG. 136. — Pine knot (a species of Peridermium), on Scotch pine. 1. The branch on the left is seen with a good-sized knot which is covered with the conspicuous clusted-cup spores. The branchlets of this branch are seen to be thicker than the normal branches; the leaves are shorter and not as green and die early. 2. Section through a knot. 3. Section through the same branch as shown in 2, but below the knot, showing that a very great growth has bsen caused by the parasitic fungus in 2. Original. In view of our lack of knowledge of the life history of these forms no preventive methods of combating this disease are known. All diseased branches should be cut off and burned as soon as they are discovered. Leaf rust of pines (Species of Peridermium). This is a close relative of the stem rust of pines. It is likewise a rust fungus ; Minnesota Plant Diseases. 277 but attacks the leaves instead of the stem. The attacked leaves are often normal in appearance and not at all distorted. The cluster cups are formed on the surface of the leaves in the spring. They are large, swollen, sac-like affairs and contain a powder of light-yellow spores. It is possible that this is the same fungus which forms its summer and winter spores on asters and goldenrods and which is there known as the aster and goldenrod rust. The leaf rust of pines is seldom present in sufficient quan- tities to injure the trees seriously. Ash leaf rust [Pncchiia fra.rinata (Lfe.) Arthur.]. Ash leaves are attacked by a cluster-cup rust which is not at all uncommon in the state, though it does not seem to be abundant. Several species, including the green ash, are the hosts. The cups are formed on large yellow spots on the leaf blade or petiole and the infected portion is often considerably distorted. The dust of spores is a bright orange red. Within recent years this clus- ter-cup stage has been shown to be connected with winter spores on the common grass plant, Spartina cynosuroides. (See also Fig. 75.) Witches'-broom of balsam fir (Aecidium elatinum Alb. et. Schw.). There are formed on the balsam firs throughout the northern part of Minnesota peculiar bush-like branch-growths known as witches'-brooms. The production of this bush is due to the. action of a rust fungus, which lives in the tissues of the branches. The first result of the attack of the parasite is the formation of a spherical swelling on the side branch of the balsam fir tree. From this swelling arise a very large number of branches, which grow very fast and become much longer than the unaffected branches. They often have a somewhat climbing, twining habit and grow upward instead of in a hori- zontal direction as do the ordinary lateral branches. The dis- eased branches do not hold their leaves through the whole year but shed them every fall. The fungus forms cluster-cups on the leaves of the broom shoots in great abundance in early summer and when the spores are ripe, a cloud of yellow dust of cluster-cup spores can be shaken from the broom. The broom increases in size from year to year and often several brooms are developed on the same tree. In some cases, almost the entire tree may be broomed. Not only is the symmetry of the growth 278 Minnesota Plant Diseases. of the tree interfered with but the tree is usually stunted and may eventually die. The leaves of the diseased shoots contain less leaf-green and are paler in color than the ordi- nary leaves. The exact method of the infection by spores in this country is not yet known. A similar disease on the silver fir in Europe has recently been thoroughly investigated. It is found that the cluster-cup spores of the silver fir brooms can- r- -^ not infect the silver fir leaves but can cause infection on certain plants be- longing to the pink family, e. g., the common chick- w e e d s. Here the fungus gives rise to the summer- and winter-spore stages. From the winter- spore forms infec- tion of the silver fir takes place. The commencement of the characteristic broom-like growth of the branches takes place in the 7 FIG. 137.— Poplar leaf rust (Melampsora populina). A lOllOWing year. No poplar leaf showing the fine, black spots of the crust- experiments h a V e like clusters of winter spores on the under surface. Original. yet been carried on to determine wheth- er or not the American fungus on the balsam fir is or is not identical with the European form on the silver fir. All brooms should be removed and burned especially before the formation of the cluster-cup spores in the spring. (See Fig. 23.) The poplar rust [Melampsora populina (Jacq.) Wint.}. The poplar rust is exceedingly abundant in Minnesota and in some cases probably effects considerable damage of young poplars Minnesota Plant Diseases. 279 and cottonwoods. Older trees are seldom if ever seriously affected. Only the summer and winter spores occur on the poplar and cottonwood while the cluster cup stage is found on some other plant. The summer spore groups are small, bright-yellow, resin- like cakes before maturity and when ripe produce a bright- yellow powdery mass of spores. Abundant, sterile, club- shaped cells are found intermixed with the summer spores. The summer spores are very abundant on poplar leaves in August. In early autumn the winter spores commence to form and soon, small, dark-brown, crust-like spore groups are produced, which later become black in color. Fallen pop- lar and cottonwood leaves, particularly those from the lower parts of the trees, are often entirely blackened and the under surface is almost completely covered with the black crust of winter spores. The winter spores pass the winter on the fallen leaves and in the following spring germinate without separating from the spore group. In case of a serious epidemic the leaves should be collected and burned in the fall. The birch leaf rust [Mclampsora betulina (Pers.) Wint.}. This rust is closely related to that of poplars and the rotation of spore forms is similar. The appearance of summer- and win- ter-spore forms also resembles the rust of poplars. The willow leaf rust [Melampsora salicis-caprde (Pers.) Wint.']. The willow leaf rust is exceedingly abundant on all the species of willow in Minnesota. This rust is also similar in general to that on the poplar leaf and is a closely related form. The leaves of younger shoots are not uncommonly so badly af- fected that they shrivel up and die. The winter spore groups form similar black crusts to those of poplar rusts and rest over winter; the spores germinate the following spring. This dis- ease occasionally occurs in sufficient amount to threaten seri- ously the cultivated willows. When occurring in such trouble- some quantities the fallen leaves with their winter-spore groups should be burned in late fall. The cedar apples of red cedar (Gymnosporangium macropus Link and G. globosum Far 1.). (See Leaf Rust of Apples — Dis- eases of Orchards.), 280 Minnesota Plant Diseases. Rust of pyrola \Chrysomyxa pirolae (DC.} Rostr.]. The cluster cup stage probably occurs on some conifer. See Dis- eases of Wild Plants. Rust of milkweeds \Cronartium asclepia- deum (Willd.) Fr.]. Sometimes found on oak leaves. See Dis- eases of Wild Flowers. The cluster-cups are probably produced on pine leaves. See Leaf Rust of Pines. Dis- eases of Timber and Shade Trees. The mistletoe dis- ease of spruce [Ra- zoumofskya pus ill a (Peck) Kuntze]. This parasite is a flowering plant of the mistletoe family, and is the only plant of this family which is native to o in- state. It produces a very serious disease of the spruce and both white and black spruce are a ff e c t e d. The presence of the para- site in the tree can usually be discovered from a distance by the presence of large "w i t c h e s'-brooms." The part of the spruce which is attacked mul- tiplies itS branches and SO pIG. 13S.— Willow leaf rust (Melampsora salicina). A willow leaf almost covered with the crust-like clus- ters of winter spcres. Original. Minnesota Plant Diseases. 281 clustered that the so-called broom looks like a foreign bush growing on the spruce tree. In badly infected trees the whole plant may consist of bunches of these brooms. By the death of the lower broom-branches, the tree may be left with only a few brooms remaining at the top. The symmetry of the tree is therefore entirely destroyed and the natural growth is very seriously interfered with. Whole forests in Ot- tertail and Becker counties are badly infested so that in many cases a majority of the trees are diseased. It has also been re- ported from Itasca county. In view of the decline of the pine forests and the growing importance of the spruce, this disease will later prove of very serious consequence. It is not appar- ently common on the north shore of Lake Superior but will probably reach all of the spruce-growing regions of the state in the course of time unless measures are taken to prevent it. The parasitic plant is very small, seldom an inch in length, and its parasitic habit has greatly affected its structure. The leaves are reduced to mere scales and the very short stem is reddish or only slightly greenish. It is rooted in the branches of the spruce tree from which it derives its nutrition. Many plants often arise from the terminal region of a single spruce branch. The flowers are very much reduced in structure and are of t\vo kinds, staminate and pistillate, growing on separate plants. The seeds are produced in berry-like fruits and are provided with sticky envelopes by means of which they cling to the branches of the trees. They are probably distributed by birds. The only known remedy is the destruction of the infected trees, which will prevent the spread of the disease. This can easily be effected when the trees are bad'y diseased for the lat- ter can be readily recognized by the brooms and the general irregularity of growth. Care should be taken to find those in the early stages of infection- for such trees have not yet devel- oped conspicuous brooms and may still harbor the parasite and thus become the center for new infections to the neighboring trees. (See Figs. 24, 25, 101.) Downy mildew of seedling trtts(Phytophthora omnivora De Bary). See Diseases of Greenhouse and Ornamental Plants. Chapter XVIII. Diseases of Field and Forage Crops* Jff The rusts of wheat and other cereals [Puccinia graminis Pers., P. rubigo-vera (DC.} Wint., and P. coronata CdaJ]. What is commonly known as wheat rust may be due to one or more of a considerable number of rust fungi. These fungi, moreover, may be found on a large number of grasses. The three most important forms of cereal rusts are : the Black or Stem Rust (P. graminis), the Orange Leaf Rust (P. rubigo-vera) and the Crown Rust (P. coronata). In all of these forms, the sum- mer and winter spores are formed on the plants of cultivated cereals or of wild grasses and in the former case (i. e. sum- mer- and winter-spore stages), cause annually an enormous .amount of damage. The summer spores first appear in early summer and are formed with great rapidity so that as the grain is growing the disease is also rapidly gaining ground. These spores occur in red lines, crowded between the parallel veins of the leaf. This form is commonly known as red rust and is particularly in evidence after very moist weather con- ditions, for these are very favorable to the rapid development of the fungus parasite. Toward autumn the production of the summer spores decreases and the formation of winter spores be- gins. These are produced in long black lines, chiefly on the •stalks and form what is commonly known as black rust. The orange leaf rust makes, as one might say, a specialty of the red rust, or summer spore stage, so that this is the prominent feature of this particular rust. On the other hand the most abundant spore of the black rust is the winter spore, hence its 'Common name. But it must be understood that the orange leaf rust also produces winter spores, and that the stem rust produces summer spores and that both have cluster cups. The crown rust also produces three kinds of spores on its para- sitic mycelium. The three rust species can be distinguished first Minnesota Plant Diseases. 283 by their life-histories and second under the micro- scope, chiefly by the shapes of the winter spores and the forms of the spore clusters. The summer and winter spores may arise from the same mycelium. The winter spores remain unchanged throughout the winter and in the spring under favor- able conditions of moisture and heat produce from each cell a short thread or promy- celium, which gives rise to four little spores known as sporidia. These sporidia are borne by the wind to other plants, where they germinate and produce a parasitic my- celium, from which arise the cluster cups and pycnidia. In the stem rust this clus- ter-cup stage is formed on barberry leaves, in the or- ange leaf rust on certain borages, as hounds-tongue (in Europe), and in the crown rust on the buck- thorn (species of. Rhatnnus). The last is very abund- antly found in Minnesota on the alder-leaved buck- thorn (Rhamnus alnifolia). These cluster cups are usual- ly formed on the under leaf- surface of their host and are formed on yellowish spots. FIG. 139. — Wheat rust (Puccinia graminis). Stems of wheat showing opened and un- opened black clusters of winter spores. This is commonly known as "black rust" or "stem rust." Slightly magnified. Orig- inal. 284 Minnesota Plant Diseases. The leaf underneath the spots is abnormally increased in size and distorted in shape. The pycnidia usually accompany the cluster cups and come from- the same mycelium1, but are gen- erally to be found on the upper surface of the leaf. They are probably male-cell receptacles which have lost their fertilizing" power and are now functionless. They illustrate a persistence of a habit after its usefulness has passed, a by no means uncommon phenomenon in nature. FIG. 140. — Stem rust of wheat (Puccinia graminis). A section of such a stem as is shown in Fig. 139, highly magnified. Clusters of winter spores have broken through the skin cells of the wheat stem. The skin cells of the wheat are seen as erect chains of cells which have been thrown .back by the growing out of the winter spores. Such wounds allow the water in the stems to escape since the skin cells of the wheat, which normally prevent the escape of water, are broken. Thus the wheat plants are dried up as well as starved by the drain of the parasite. Each winter spore of the fungus is seen to be two-celled. Highly magnified. Microphotograph by E. W. D. Holway. The cluster-cup is composed of a thin wall, enclosing an in- ternal mass of orange red spores. The wall splits at the summit and opens out often in star-shaped fashion. The spores are formed in chains from the floor of the cup. The cluster-cup spores are scattered, when 'mature, by the wind and alight on some grass plant, where they germinate into a tube, which pene- trates into the interior of the host through an air-pore, and forms Minnesota Plant Diseases. 285 internally a mycelium. The latter, under the most favorable con- ditions in about eight days, and under less favorable conditions usually within two weeks, again produces the summer spores. The life-history of a wheat rust can therefore be divided int.^ three parts; first, the stage on the grass or wheat plant, producing the red (summer) and black (winter) spores in succession; second, the germination of the winter spores and the production of sporidia on the ground or in the straw in the springtime; third, the germination of the sporidia on barberry (or bor- age, buckthorn, according to the particular form of wheat rust), and the subsequent formation from the mycelium so produced, of cluster- cups and pycnidial stages. In seasons that are favorable for the development of the rusts whole crops may be completely ruined ; but the danger does not end here. Crops are often not so con- siderably affected and may appear but slightly rusted. The latter cases are often lightly passed over as of iiO' account but such is not the case. If the rust is present in any notice- able amount it is safe to say that the parasitic fungus is levying a tax of nutrition and energy upon the host or crop plant which results in crops correspondingly lighter than should be the case if no rust were present. That is tj say, the nutrition which could normally be expended in the formation of more and heavier grains is required to nourish the parasitic rust; The almost fabulous figures recorded each year as the loss to farmers by rust is more often probably underestimated than ex- I FIG. 141.— Oat stems and leaf bases with clusters of summer spores of the oat rust. The spots are large and not sharply defined. Original. 286 Minnesota Plant Diseases. FIG. 142.— Spores of the common "black rust" (Puccinia graminis) of wheat. 1. Cluster-cup spores from the barberry plant. 2. Summer spores from the wheat plant. 3. Winter spores from the wheat plant. Highly magnified. After Arthur and Holway. aggerated because the smaller losses due to the presence of the rust in very slight and therefore unheeded quantities may never be computed. These are, nevertheless, a certain loss. There is only a difference in degree. The en- tire elimination of rust would therefore increase the value of crops throughout the country by an enormous per cent. At present there is no known method for successfully com- bating wheat rust. Numerous attempts to fight the disease by spraying with bordeaux and other mixtures have always proved unsuccessful. Where stem rust is the principal form and barberry bushes are common, it has been found that the removal of barberry bushes will diminish the rust considerably. In Minnesota, however, very few barberry bushes are grown, and of these many are often not infected with grass-rust cluster-cups, while the host plants upon which the crown rust and orange leaf rust grow are very common wild plants. The cluster cup of the orange leaf rust forms on plants of the borage family, but no cluster cups have yet been found on these plants in this state, so that either our orange leaf rust differs from the European form or else it can here dispense with the cluster-cup stage altogether. Little can therefore be hoped from the removal of the cluster-cup host plants. There is still another factor which would help to de- feat such a method. In at least one of these rusts, the my- celium which produces the summer spores may live through the winter and produce summer spores again in the following summer, thus dispensing with the necessity of the cluster-cup stage. It is also possible that even in some forms, where the Minnesota Plant Diseases. 287 mycelium does not hibernate, that the cluster-cups can also be omitted without injury to the rust. It is an important fact that some of the injurious rusts are found upon wild grass plants and infection from cereals from such sources must not be overlooked. The stem rust in par- ticular is dangerous on this account. It has been shown that the stem rust of wheat is able to infect a half dozen or more com- FIG. 143. — Spores of crown rust of wheat (Puccinia coronata). w. Win- ter spores, with a crown of finger- like protuberances at the top of each spore; from the wheat plant, s. Summer spores from the wheat plant, c. Cluster-cup spores from the alder-leaved buckthorn. Highly magnified. After Arthur and Hoi- way. mon wild grasses, including squirrel tail grass (Hordeum jubatum), and also that the rust from these can infect wheat plants. This is a very discouraging feature, for it seems almost impossible to eliminate all of these weeds. Unless this is done, however, the spread of stem rust cannot be pre- vented. The stem rust moreover is the most virulent rust for the spore specialty is the winter spore and this is found chiefly on the stems, hence the common name of stem rust. In this posi- 288 Minnesota Plant Diseases. tion the mycelium rapidly drains away the nourishment which should go to the heads and allows of an uncontrollable evapora- tion of water through the broken skins; as a result the berries do not fill but remain shriveled. Such wheat therefore, even if not entirely ruined, suffers a loss of grade. FIG. 144. — Cluster-cups of the crown rust of wheat (Puccinia coronata), on swollen cushions of the stem of the alder-leaved buckthorn. Photograph by Arthur and Holway. It is also known that in states south of Minnesota the sum- mer spores of grass rusts live through the winter and cause direct infection of the grass plants in the spring. It is not impossible that these spores from southern states can rapidly work their way north in the early spring and commence the infection each Minnesota Plant Diseases. 289 year. The rapidity of formation of successive crops of summer spores would make this manner of spreading easily possible. Eriksson, an eminent European specialist on rusts, has pro- posed a theory known as the mycoplasm theory, which supposes that the fungus threads live over in the grain of the wheat as an amorphous substance, totally unlike the ordinary fungus threads. This mycoplasm he supposes to be diffused amongst the protoplasm of the cells of the grain, until the latter com- mences to germinate, when it again assumes the form of threads and causes an infection of the seedling wheat plant. We can- not here go into the details of the evidence, but in the opinion of a great majority of rust specialists this theory has not suffi- cient foundation. Infection by the spore methods, described above, is at present the only known method. Recent work points to more probable success in combating rusts along another line. It has been found that many of the rusts are so closely adapted to the conditions found in the plants, on which they occur, that they have great difficulty or fail en- tirely in growing upon other varieties. At present there are recognized, by the best authorities on the rusts of cereals, more than a dozen distinct varieties and species. Many of these are indistinguishable from other forms, as far as external characters are concerned, even with the aid of powerful microscopes, but a great difference is soon found when the spores are germinated and infections attempted. It is then seen that some forms are so especially adapted to the species or variety of the host plant, upon which they occur, that they refuse to develop on other varieties or species of the same genus of host. Such rust forms are called "biologic" species. On the other hand it will be seen that some species and varieties of grasses and cereals may thus be immune from some forms of rusts. A "rust-proof" variety would not of course be proof against all forms of rust but might be immune from certain forms. Consequently something bene- ficial may be expected from the efforts of plant breeders in the production of rust-proof cereals. With intelligent care in the selection of cereal varieties and with a broader and better knowl- edge of the habits and life-history of the parasitic plants causing rusts, it is very probable that the ravages of this disease can be at least considerably checked. 19 2 go Minnesota Plant Diseases. In the production of rust-proof varieties the selection of seed becomes of great importance. Many farmers instinctively believe that seed from rusted fields will necessarily produce a rusted crop. Such is not the case as can easily be seen by a perusal of the above life-history of the rust. The rust does not live over in the seed and seed from rusted fields have no more chance of becoming rusted than that from fields that have had no rust, provided, of course, that it is not shriveled or in other way dam- FiG. 145.— Cluster-cups of the black or stem rust of wheat (Puccinia graminis). on stems and leaves of Barberry. Photograph by Arthur and Holway. aged. In fact good seeds from rusted fields should be highly prized for seeding purposes since they indicate that the plants which bore them were probably rust-resistant. It would there- fore be advisable to select seed from rusted fields, but such seed must be carefully cleaned and graded so that only strong and healthy berries are used. Of seed from regions free from rust nothing definite can be predicted. The absence may be due to rust-resistance or it may be due to an absence of the fungus in Minnesota Plant Diseases. 291 that locality. In the former case the seed would of course be valuable, in the latter it might easily fall a prey to the first attack of rust. It must further be pointed out that the conditions in a given community must be thoroughly known, i. e. the chief kind of rust and the conditions favoring its spread, as alternate host- plant, etc. The problem, therefore, may divide itself into special sectional problems. Again any new rust-proof varieties may not always remain so, for the rusts can vary and adapt themselves to new hosts and may at some future time find a way to invade the new rust-proof variety. It seems therefore that the problem before us is not one to be dispensed with by one discovery, but that it may involve a long series of breeding experiments — in other words, a continuous fight. It seems furthermore reason- able, when all evidence is weighed, to hope that in such a com- bat the plant breeder will ultimately emerge victorious. (See also Fig. ii and Chapter XI.) In view of the importance of wheat rusts, detailed accounts may be of value, and are given below for the benefit of those who may be especially interested in this subject and who may wish to be able to determine the chief rusts in the field or laboratory. The italicized portions point to distinguishing differences. The crown rust occurs chiefly on oats, more rare- ly on wheat. In can be recognized microscopically by the crown of prejections at the end of the winter spores. (See Fig. 143.) The two remaining are the important wheat rusts. The orange leaf rust (commonly called "red rust"}. The clus- ter-cups are unknown in this country (except for a form on Elymus with cluster-cup on Impatiens). The summer-spore- clusters (so-called "red rust") : chiefly on the lower surface of the leaf blade, often abundant; occasionally on the leaf sheath; small, oblong, up to i m. m. long, usually arranged in rows and often running together forming long lines, orange-colored when fresh. The summer spores (under the microscope) : globose or soment'Iiat globose or broadly elliptical, finely spiny, orange- colored. The winter-spore-clusters : accompany and follow summer spores ; on the leaf blade (seldom on the stem) ; arranged in lines or scattered ; oblong, dark brozvn or black; remain covered by the host epidermis for a long time. The winter spores : club- shaped, rounded or truncate or conic at the apex, slightly con- 292 Minnesota Plant Diseases. stricted near the middle, two-celled, brown, smooth, have a short stalk or none; accompanied by sterile threads (paraphyses). The stem rust (commonly called "black rust"). The cluster- cup grows on barberry. The summer spore clusters : chiefly on the leaf sheath, occasionally on the stem, seldom on the leaf blade; scattered or in rows, elongated or linear, (2-3 m. m. long), often running together to long lines ; bounded by the fissured epider- mis of host, becoming powdery, brozvn when fresh, yellozv when dry. The summer spores : usually ellipsoidal or ovate oblong, finely spiny, yellow brozvn (when fresh). The winter spore clus- ters (so-called "black rust'7) : chiefly on the stem or on the leaf sheath (less common on the leaf blade) ; scattered or in rows, elongated, often running together into long lines, i. c. m. or longer; soon exposed (naked) by the breaking of the host epi- dermis, black and powdery. The winter spores : oblong or club- shaped, two-celled, smooth, chestnut brown; apex rounded or long-conical and much thickened; base attenuate; have brown stalks, often as long as the spore; no sterile threads. Rust of corn (Puccinia sorghi Schw.). This very common rust occurs on species of sorghum and on corn. The cluster-cup stage has recently been discovered; summer and winter spores are well known. The two latter spores occur in usually small, sometimes considerably elongated, groups or sori of red- or red- dish-brown color. The winter spores are two-celled. The clus- ter-cup is found on a species of Oxalis. This rust is usually not in sufficient abundance to cause any serious loss. Clover leaf rust [Uromyces trifolii (Hedw.) Lev.]. The clover rust occurs on several kinds of clover, notably on red and white. Cluster-cups are formed, but not commonly, in the spring, on the petioles and blades of the leaves, and summer and winter spores are found later appearing as red and brownish powdery spots, usually on the under surface of the leaf. The win- ter spores are single-celled. The fungus thrives in damp cold sum- mers and is usually not abundant or dangerous in the spring; but it may increase during the summer, especially if conditions are favorable. The early red clover crop is therefore usually unaf- fected, but later crops may be damaged. The plowing under of later crops when badly infected has been recommended, as has also the burning over of the fields to prevent a recurrence of the disease in the following season. Minnesota Plant Diseases. 293 Loose smut of oats [Ustilago avenae (Pers.) fens.]. This exceedingly common and destructive disease is very well known on account of the enormous damage which it yearly causes to oat crops. In the United States alone, losses of many millions of dollars year- ly, by oat smut, have been re- corded. The application of Jen- sen's Hot Water Method and the formalin treatments have in recent years greatly de- creased the loss by this disease. When an oat plant is at- tacked, usually all of the heads, and all of the grains in each head, become smutted. Very few if any grains escape in a smutted plant and those that do are always stunted. The stamens of the flowers as well as the ovaries are attacked by the fungus. The grain is con- verted into a large sac with a very thin membrane complete- ly filled with the black spores of the fungus. The smut spores are blown about by the wind before harvest time and become attached to healthy grains or fall on the ground. In the following year when the oat grain has commenced to sprout, the fungus spores also germinate. A spore in germination first forms a very short chain of cells, which bud off from their sides little secondary spores. These spores sometimes fuse in twos, thus probably gaining in strength by uniting forces. The spores either with or without fusion may continue to bud off other spores when placed in favora- ble nutritive conditions such as a culture medium. They FIG. 146. — Loose smut of oats. Original. 294 Minnesota Plant Diseases. are produced in yeast fashion. This is an important fea- ture, for the fungus may thus continue vigorous in such places as manures for an indefinite length of time. Any of these spores, when placed under favorable conditions, can send out a small germ tube which, when it comes into contact with the seedling of an oat plant, will pierce the sheath of the seedling and make its way to the little mound of growing tissue at the tip of the stem. The fungus branches here freely and es- tablishes itself, as a well developed mycelium, between the cells of the host plant. There is no external mark by which such a plant can be distinguished from a healthy one until the forma- tion of the grain. The attacked plant appears perfectly normal. The fungus in the growing point keeps pace with the latter in its growth. The fungus threads disappear in the older tissues so that the mycelium can usually only be found in the region of the growing point. When the oat stem branches the fungus es- tablishes itself in the growing point of the branch as well as in the growing point of the main stem and this accounts for the fact that usually all heads of an attacked plant are smutted. When the head commences to form, the fungus invades every flower and in the organs of the latter it forms its smut spores in great abundance. It is not until this period that the fungus comes into evidence. Every grain is thus attacked and filled with the smut spore powder. One well known method of prevention of oat smut is the hot water treatment. This has in general been replaced in recent years by the formalin method. Both of these treatments are de- scribed under Steeps in Chapter XV. By both of them the smut spores which cling to the grains are killed off, while the grains themselves are not injured. Infection in oats is dependent on the bringing together of germinating smut spores and seed- ling oat plants, and the destruction of the smut spores attached to the grain very considerably lessens the danger of infection, as it is from these spores that infection generally takes place. The smut spores also germinate most readily at about 50 degrees Fahrenheit or about the out-of-doors spring temperature, and their ability to germinate decreases with the rising temperature. For this reason late sowing is sometimes recommended. This is however entirely unnecessary when the above methods of pre- vention are used. Minnesota Plant Diseases. 295 Stinking smut of wheat [Tilletia tritici (Bjerk.) IVint.]. This is a common smut-fungus of wheats and is well known to be very destructive. The fungus gains entrance to the plant, when the latter is still a seedling, and keeps pace with the growth of its host, until flowering time. The mycelium then invades the ovaries and replaces the contents of the latter with fungus threads. These threads form an oily or greasy mass which is later transformed into the smut powder. The smut spores are blackish in color and have, in bulk, a very disagreeable odor, which gives rise to the common name of the disease. The smut- ted ovaries do not open until harvested. Smutted heads are usually erect and can be detected in the field at harvest time. The presence on smutted grains in quantity amongst the healthy is a very serious damage as it unfits the crop for use as flour, unless the smut is cleaned out by a special process. When smutted grains are fed to animals the results are sometimes seri- ous. Corn smut, and other smuts of grasses are known to have injurious effects upon animals. Horses, cattle, sheep and swine may be affected. Not much is known about the specific results of poisoning from each kind of smut, so that confusion as to symptoms exists. "As a result one generally finds a continuous movement of the jaws, and a flow of saliva, also lameness, stag- gering and falling." (Tubeuf and Smith, p. 306.) The stinking smut of wheat differs in its development very radically from the smuts of the group to which the loose smut of oats belongs. When the spore of the latter germinates a fine tube is produced which is divided into a row of cells, each of which buds off tiny, oval or spherical spores from, the side of tube. In the stinking smut of wheat, the tube of the germinating smut spore is not divided into cells but forms its spores from the end of the undivided tube. These secondary spores may fuse to- gether in twos and from the fused cell, a third crop of spores may be formed. Any of these secondary or tertiary spores are capable of growing out into a fine tube ; when it comes into contact with a wheat seedling this tube penetrates into the tissues of the stem and so begins its parasitic life. The life of such a smut can therefore be divided into two stages; first, the parasitic stage, beginning with penetration of the infection tube and ending with the formation of the smut spore powder; and second, the 296 Minnesota Plant Diseases. saprophytic stage, beginning with the germination of the spore and ending with the formation of an infection tube by the sec- ondary and tertiary spores. The secondary and tertiary spores, produced by the smut spore, are capable of living in a nutrient solution or in fresh manure, where they may form a saprophytic mycelium or may continue to bud off more spores in a yeast-like fashion. They may live thus for years, and when finally brought into contact with the seedling plant, they may still cause infection. FIG. 147. — Stinking smut of wheat. 1. A head of wheat with smutted grains (smutted grains are colored black). 2. Small portion of a head showing smutted grains which are fissured, and show the black spore mass within. 3. Isolated grains which are smutted and have fissured walls. One grain is sectioned. 4. Smut spores germinated and producing at the end of the germ tube long, needle-like spores, which sometimes fuse together in pairs by cross-threads as shown on the left. 5. The thread spores, shown in 4, in germination sometimes again producing secondary spores. 6. Smut spores germinating to long infection threads without first forming spores. 4-6 highly magnified. After Tubeuf. The treatments used for loose smut of oats are also effective against this disease. The Jensen hot water method (see chap- ter on Prevention), has -been found useful, but the most effective and easiest method is the formalin treatment, which has practi- cally supplanted the former. This smut can in practice be en- tirely prevented by this method. Minnesota Plant Diseases. 297 Loose smut of wheat [Ustilago tritici (Pers.) Jens.]. This smut is also known as wheat brand. It is a destructive smut of wheat and differs in many ways from the stinking smut. It can be distinguished, botanically, by the behavior of its spores since they develop at germination a chain of cells similar to the loose smut of oats, instead of an undivided tube, as in stinking smut of wheat. From this chain of cells are budded off the secondary spores, which behave as do those of loose smut of oats. In other characters, which are visible to the naked eye, this smut is well marked off, from the stinking smut of wheat. The smut masses are formed in the place of the grains, and may even supplant the chaffy scales. This smut mass does not remain closed until har- vest time, but opens at flowering and the spores are scattered by the wind. At harvest time, therefore, only the bare stalks of the wheat heads, with remnants of scales, remain on the plants. This method of distribution gives rise to the common name of loose smut. The spore mass is a dark, olive-green, dirty mass which differs from the stinking smut in the absence of any fetid odor such as the latter possesses. No sure method of prevention is known. A modification of the Jensen hot water process for loose smut of oats has given some relief, but seems to injure the seed. The formalin method is also uneffective. The only relief known at present is the selec- tion of clean seed, which can only be done by obtaining the seed from a smut-free district. (See Fig. 72.) Corn smut [Ustilago maydis (DC.) Cda.]. The smut of corn is a disease familiar to every farmer. It may attack almost any part of the plant, but is particularly abundant upon the cobs, staminate tassels and the leaves. When a cob of corn is attacked a number of the grains become enormously enlarged and are covered with a thin, whitish-grey membrane. The whole cob may thus be enlarged to twice its natural size. The interior of the affected grains is filled with a blackish to dark green pow- der of smut spores. When a leaf is attacked, tumor-like swell- ings are produced, which often become as large as an apple and this tumor contains the blackish spore-powder. Upon the staminate tassels, smaller tumors are formed which are of a similar structure to those of the leaf. The smut spores rest through the winter. In the spring they germinate, producing 298 Minnesota Plant Diseases. small tubes which bear secondary spores in great abundance; these spores are capable of yeast-like budding when brought under favorable conditions, e. g., in piles of manure ; in this manner the infecting ability of the disease is greatly increased. These secondary spores are conveyed by the wind or other agency to other plants and infection follows. Only young parts of the plants can be successfully attacked. The disease is only local in its effects, and in this character it differs very de- cidedly from such smuts as loose smut of oats and stinking smut of wheat. The part most fre- quently attacked is the cob and the harvest is often seriously diminished by this disease. Cer- tain varieties of sweet corn are peculiarly susceptible to attack, so that a selection of varieties is often advisable. Treatment of seed corn with copper sulphate or formalin has absolutely no effect on this smut. If the disease has been bad in the preceding year, fresh manure should be avoided, as the multi- plication of the spores is in- creased by its use. All smut tu- mors and spore masses must be burned as soon as discovered. Bordeaux spray has been found successful to a certain extent, but usually is unnecessary if the spore masses are carefully removed. Head smut of sorghum [Sphacelotheca reiliana (Kuhn.) Clin- ton]. This smut attacks the whole head of the sorghum plant and often all of the heads of a plant. The smut mass therefore replaces the entire head and is at first surrounded by a fine white membrane, which later ruptures and exposes the smut' powder. Grains, glumes and all parts of the head are de- FiG. 148. — Smut of corn (Ustilago may- dis), on left, on the leaf of the corn; on the right, in the tassels (stami- nate inflorescence). After Clinton. Minnesota Plant Diseases. 299 stroyed and only the loose strings of the woody tissues of the head branches remain. The head smut can be distinguished from the grain-smut by this habit. The smut mass forms a blackish powder. No preventives are known for this smut. It is possible that the treatment for grain smut will be effective. Grain smut of sorghum [SpliacclotJicca sorghi (Lk.) C lint o n]. This sorghum smut attacks the young grains and forms smut masses in them, but does not destroy the glumes. The smutted grains increase in size, chiefly in length, and have a whitish wall which encloses a mass com- posed entirely of spores. The spores rest over winter and under proper condi- tions, in the spring time, form more spores, which can in turn multiply in yeast-like fashion; the re- sulting spores are capable of causing infection. Sorghum is also fre- quently attacked by other smuts and certain varieties of the sorghum are known to be peculiarly susceptible to smut. (See also Head Smut of Sorghum.) A few experiments on this smut have indicated that hot water treatment may be beneficial. It has proved successful in the treatment of the same smut on broom corn. It is also possible that the for- malin method would be effective and useful. FIG. 149. — Corn smut (Ustilago maydis), on an ear of corn. A few of the kernels near the butt have not been smutted. All of the others have been attacked and have in- creased enormously in size. The enlarged kernels are filled with the smut powder. Original. ^oo Minnesota Plant Diseases. «j Broom corn smut [S phacelotheca sorghi (Lk.) Clinton]. This is the same fungus that causes the grain smut of sorghum. When it attacks the broom corn, it seriously affects the forma- tion of the brushes and the smut often discolors them. The young grains and stamens may become smutted and usually all of the grains of a cluster are destroyed. The spore mass is very dark and the spores have an olive-colored tint. The host plant is apparently infected only in the seedling stages and hence care must be taken to avoid the presence of spores in a seed mixture. Seed broom-corn should be treated in hot water in the usual way at a temperature of 135 degrees Fahrenheit for ten to fifteen minutes. Such treatment of seed will largely if not entirely pre- vent the smut. It is probable that the formalin method would also be effective. Naked barley smut [Uslilago nuda (Jens.) Kell. and Siv.~\. The naked smut is more common than the covered smut of bar- ley and also more difficult to combat. This smut attacks the grains and forms smutted heads, which do not, however, remain closed as long as do those of the covered smut. The smut masses are at first enclosed in a membrane, but the spores do not adhere so closely and when the membrane of the head breaks the smut spores are quickly dispersed by the wind. The heads of barley have then the appearance o>f wheat affected by loose smut. The awns of the barley head are either only stunted or may remain intact. The powdery spore mass is dark and black, with a greenish tinge, differing in this respect from the cohered smut of barley. The exact method of infection of the host plant is unknown but there seems to be some evidence that it is not in the seedling stage. "Soak the barley seed four hours in cold water and then let it stand four hours longer in a wet sack. Finally dip and drain as directed in the treatment for oat smut for five minutes in wa- ter at a temperature of 126 to 128 degrees Fahrenheit, after which dry and plant as in case of smut of oats." (Kansas Ex. Sta. Rep. for 1889, p. 284.) This treatment is also ample for the covered smut. Covered smut of barley [Ustilago hordci (Pers.) Kell. and Sw.]. This is one of the two common smuts which attack the barley plant. The smut spores are formed in the very young Minnesota Plant Diseases. 301 302 Minnesota Plant Diseases. T3-C « ! £~gj S-d " Minnesota Plant Diseases. grains, but are not scattered immediately after ripening. They are enclosed in a membrane which includes the scales around the grains. Not all of the interior of the spikelet is converted into spores, but plates and shreds of material remain, which are not smutted. The spores are therefore held firmly together and the smut is thus known as the covered barley smut. The spores are black when seen in mass and have no greenish tinge. On ac- count of the compactness of the smut heads, the disease does not spread with very great rapidity. It is not known whether the spores infect the seedling barley as in oat smut or cause in- fection later, as in the corn smut. The hot water method and the copper sulphate steep have both been recommended. The treatment used for the naked bar- ley smut is said to be effective against the covered smut. The formalin method would probably be oi use. Brome smut (Ustilago brornivora Fisch.). Brome plants are subject to smut attacks and the spore masses are formed in the young grain. The heads of grains do not show any abnormal growth. The spore mass is usually black. Millet smut (Ustilago crameri Korn.). A smut attacks millet plants and is sometimes abundant. At flowering time, the fun- gus replaces the ovaries with black masses of the smut spores. All of the heads of the attacked plants are smutted. The spores germinate in the usual way, forming a small tube from which, however, secondary spores are not usually, if ever, produced. Care should be taken to use clean seed free from smut. The hot water method has been found to be an effective preventive. Leaf smut of rye [Urocystis occulta. (Wallr.} Rab.]. This fungus attacks several cereals but is most frequent on rye. It has not been reported as very frequent in this country and it is probably not at all abundant in this state. It is unlike most of our common smuts in many of its characters. The spores are formed in elongated lines on the leaves and stem, which are at first greyish but later, after the bursting of the epidermis, exhibit a black powdery smut-mass underneath. The whole plant is de- formed and injured. The spores are aggregated together into true spore-balls. About a half-dozen spores cling together into a solid mass, in which a differentiation oo6 Minnesota Plant Diseases. \j are borne on the ends of beaded threads and are two-celled. The spore-sac capsules are borne in a blackish cake of mycelium, somewhat similar in appearance to the tar-spot of willows. The fungus is also known on the scarlet clover (Trifolium incarna- tum). It is sometimes known as the black mold of clover. Smothering fungus of grasses [Epichloe typhina (P.) Tnl.]. This disease is also known as the Reed Mace Fungus. It is found on grasses and is apparently confined to a few genera. It some- times causes injury to fodder grasses. The fungus attacks the above-ground portion of the grass and forms white or light tan- colored cushions of mycelium around the leaves and stem of the host. These cushions are so dense that they prevent further growth of the leaves and stem, causing, as it were, strangulation. From this cushion arise first, small colorless spores on short stalks. These are the summer spores, comparable to those of the powdery mildews. Toward fall the sac-spore-capsules are developed. They arise in great numbers, embedded in the outer part of the cushion and are of the same color as the cushion. They are long and pear-shaped, and open to the surface by means of a pore at the end of a slightly protruding neck. In each capsule a large number of sacs are produced in a group, on the floor of the capsule cavity, and each sac contains eight spores. The spores are very long and thread-like and are di- vided into many cells, arranged in a chain. When ripe, the spores may break up into segments, each of which is capable of germination, producing a mycelium and causing infection. The fungus, when occurring in great abundance on fodder grasses, is said to be injurious to the feeding horses. It sel- dom becomes a serious pest. (See Figs. 57 and 58.) The ergot disease of grasses [Claviceps purpurea (Fr.) Till and other species]. The ergots of grasses are very closely related to the smothering fungus of the same plants. The ergot fun- gus attacks the very young and immature grains and the my- celium soon permeates the tissues of the grain. It replaces the latter entirely and forms in its stead a dense mycelium which soon becomes so densely interwoven that it forms a solid body of characteristic form and of doughy consistency. The outer surface of this body is at first thrown into folds and ridges and along these folds one finds the summer spores produced in Minnesota Plant Diseases. 307 great numbers. These spores are small, oval, or cylindrical, colorless ceils. Their production is accompanied by the secre- tion of a sugary fluid known as "honey dew/' which is at- tractive to insects. The latter in their search for the "honey dew" distribute the summer spores from plant to plant and rapidly spread the disease. Toward the end of the summer, the formation of summer spores ceases and the underlying fun- gus mass becomes more compact and hard, and the external threads form several layers of cells which contain a very dark purple coloring matter. This fungus mass is now known as the sclerotium and is the ergot of commerce. The form of the ergot varies in the different grasses. The ergot of rye (commercial er- got) is long and cylindrical and slightly curved. The er- got of wheat is much shorter and thicker, while the ergot of wild rice is still shorter and roughly egg-shaped. The er- got is a storage organ and usually rests through the win- ter. The storage material is a kind of starch, known as fungus starch, which is stored up in the cells. The fungus threads are so compacted to- gether that they form a mass of cells very similar in appear ance to that of the pith of some flowering plants. The ergot rests in or on the ground, where it is often sown with the grain, until early summer. Under the proper conditions of moisture it then develops further. From the surface of the ergot arise several short, violet-colored stalks, which bear at their tips yel- lowish spherical heads. The latter are the spore-sac-capsule cushions, as may be seen by the small protruding necks of the FIG. 154. — The ergot fungus (Claviceps pur- purea), on rye. The large fungus stor- age organ (sclerotium or ergot) is seen near the top of the head. After Clinton. ;o8 Minnesota Plant Diseases, FIG. 155. — Storage organs or ergots of ergot fungi on various grasses. 1. Commercial ergot from rye. 2. On canary grass. 3. On wild rice. 4. On quack grass. 5. On a reed Minnesota Plant Diseases. oOU capsules with their pore-like openings. The arrangement of the capsules is similar to that in the smothering fungus, except that the cushion is spherical in shape. In the capsules are nu- merous sacs, each containing eight spores. The latter are very long and thread-like and are many times divided by cross walls and each division is capable of the formation of a mycelium. The flowers of the grass plant are again infected by these spore- segments from the sacs. The storage-body or sclerotium is widely used medicinally and is known as the ergot of rye. In the grains of the latter it is very commonly found. These ergots sometimes attain a length of one and one-half inches. The presence of ergot amongst grains from which flour is made may give rise, among the consumers of the bread, to a disease known as ergotism. Cattle fed with grains containing ergots in considerable amounts may also be severely poisoned. Numerous cases of such poi- sonings in our northwestern states have been reported. Chronic effects, from long-continued small doses, can be distin- guished from acute attacks. The shape of the sclerotium varies with the grain, upon which it is formed. Ergots grow on many of our very common wild grasses and are sometimes here even more conspicuous than on the cereal grasses. The only preventive means for ergot lie in the destruction of all sclerotia and in the planting of clean seeds, i. e., seeds free from an admixture of ergots. Leaf spot of alfalfa \Pseudopeziza mcdicaginis (Lib.} Sacc.]. This small cup fungus causes yellowish spots upon the leaves. In the center of each spot are seen the tiny black fruiting bod- ies. These are cups of such minute size that they can be clearly seen only with the aid of the hand lens. The disease is some- times serious, and in Iowa has at times caused a loss of one- half of the crop. Frequent cutting keeps down the disease by preventing the maturing of the fruiting bodies and thus pre- venting infection. The spores mature in early summer, proba- bly in June. Diseased plants may be cut when the disease first appears. Cup-fungus leaf-spot of clover (Pseudopesiza trifolU FcklJ. This fungus occasions local epidemics among clover and lu- cerne crops. It is one of the cup fungi but the cup is so minute 310 Minnesota Plant Diseases. that, like the cup of the leaf-spot fungus of alfalfa, it can only be seen clearly with the aid of a hand lens. It appears on a leaf in small spots where the mycelium establishes itself. These spots become thickened and from the center of each the cup uncovers by the splitting out of the upper part so that a star-shaped opening is produced and the layer of sacs is ex- posed. Each sac contains eight spores. The spots may be- come so numerous that the whole leaf or even the whole plant is destroyed. The fungus may spread with great rapid- ity. Burning of the fields in fall has been recommended to prevent the reappearance of the fungus in the following year. Frequent cuttings also tend to prevent the spread of the dis- ease. Wheat scab (Fusarium culmorum W. G. Sm.\ The fungus of wheat scab is an imperfect fungus. It attacks the grains of the wheat just before ripening and causes the heads to ripen prematurely. The heads may be entirely or only partially de- stroyed. Affected parts turn whitish or are bleached. The effects often travel from above downward in the head. The mycelium runs over and through the spikelets and glues them together. A gelatinous material is formed by the fungus threads and this causes the glueing together of the spikelets. The heads turn pinkish in color and the grains shrink. The losses from this disease have at times been very serious. Poor drainage is said to increase the amount of scab. It has also been reported that strong plants will resist the scab more successfully than weak ones. No remedy for scab is at present known. Flax wilt (Fusarium lini Bolley). Flax all over the world is subject to a disease known as wilt. Whenever flax is raised continuously on the same ground for a number of years it sick- ens, and it soon becomes impossible to raise the plant success- fully. This fact has been known for a long time in Europe arid rotation of crops has long been practiced there to prevent the disease. The wilting is due to a fungus parasite which attacks the roots and stems of the flax plants in all stages. So virulent does the disease become that after six years of continuous cul- ture of flax on one plat of ground it has been found impossible to raise one plant longer than three weeks. The following ac- Minnesota Plant Diseases. 311 count is taken from a bulletin of the North Dakota Ag. Ex. Sta. by H. L. Bolley, \vho first discovered the true cause of the dis- ease. "The plants are attacked at all ages and die early or late in the stage of growth according to the time and intensity of the attack. If the soil is much affected, that is to say "flax sick," most of the plants are killed before they get through the surface of the ground. Such areas appear in a field of flax as centers of disease, which enlarge throughout the summer as new plants sicken, Wilt, and die down around the margins of the spots, finally giving the whole field a spotted appearance. Young plants two to five inches in height wilt suddenly, dry up, and soon decay if the weather becomes moist. Older plants which are quite woody take on a sickly, weak, yellowish appearance, wilt at the top, slowly die, turn brown, and dry up. Nearly mature plants which are attacked, but not yet dead, are easily pulled up, the roots breaking off easily at about the level of the furrow slice." TIG. 156.— Flax wilt. Wilted seedlings. After Bolley. "Upon examination, most of the smaller branch roots are found to be dead, as well as the tap root below the point at which it breaks off. These dead roots and the parts of the tap root already diseased have a very characteristic ashen gray color. Many nearly mature plants, which are attacked late in life, show this dead gray down one side of the tap root only. The leaves, side branches, and a strip of the main stem above this portion are dead, giving a peculiar one-sided blighting, similar to the appearance of a tree struck by lightning." "If the disease is sowed with the seed upon breaking, but a few of the plants are attacked the first year; and, at flowering time, dead plants will be seen to be quite evenly distributed in 112 Minnesota Plant Diseases. the drills. If weather conditions are quite favorable, each new infection increases sufficiently in area to reach over and attack plants in two or three adjacent drills. These infection areas are nearly always circular in outline, and become much enlarged if flax is seeded there the following year. The first year these spots may reach a diameter of one to three or four feet. The second year these same areas are usually much more than doubled, so that it takes but three to five flax crops upon such lands to make the infection gen- eral/' Diseased fields have not FIG. 157.-Sp01Psof the flax wilt fungus high- lost their fertility, as was ly magnified. After Bolley. formerly SUppOSed, but Can produce good crops of other plants, as corn, wheat, potatoes, etc. The d'sease seems to thrive on strongly alkaline lands and often under conditions of drouth. FIG. 158.— Flax wilt. The wilt fungus threads around the root of an at- tacked flax plant. Highly magnified. After Bolley. The fungus is an imperfect fungus and lives normally as a saprophyte but becomes on occasion a destructive parasite. The fungus threads live in the tissues of the flax plant root, coming to the surface of the root to produce its spores. The latter are formed in a loose weft arrangement. The ordinary spore is Minnesota Plant Diseases. 313 long spindle-shaped, consisting of a string of cells. Thick- walled spores are also produced, consisting of several cells, and are capable of resting over in the soil for some time before ger- minating. The chief method of distribution of the fungus is by means of the spores which cling to the seeds of the flax. Flax seed should therefore be treated before seeding to de- stroy the fungus spores clinging to the coats. Professor Bolley has recommended the following treatment and preventive measures : "Use formaldehyde at the rate of one pound of the standard strength to forty or forty-five gallons of water (the same strength used for wheat and oats). Spread the seed upon a tight floor or upon a canvas and sprinkle or spray on a small amount of liquid (a fine spray is best). Shovel, hoe, or rake the grain over rapidly. Repeat this spraying, shoveling, hoeing or raking until the surfaces of all of the seeds are just evenly moist, not wet enough to mat or gum, but evenly damp. (This can be done without matting if the grain is well hoed or shoveled over while the solution is slowly and evenly sprayed upon it.) When the seeds are just evenly moist, cease applying the solution, but continue to shovel the grain over so as to get it dry as soon as possible. Avoid any excess of moisture. If flax seeds are dip- ped in the solution or are al- lowed to get enough to soften the seed coats so that they will stick together, they will be con- siderably injured or even killed. "It takes less than one-half gallon of the solution to properly moisten one bushel of flax seed. "Caution: One must treat flax with much more care than that usually taken in treating wheat or oats for smut. The solution recommended is strong enough to kill all seeds, if they are made thoroughly wet, or if they are allowed to stay quite damp for some hours. Fie. 159.— Flax wilt. A section of a flax root with fungus threads and spores at the surface. Magnified. After Bolley. 314 Minnesota Plant Diseases. "The grain must be handled over immediately after treat- ment until it is found to be dry. "Note: The seed should be thoroughly cleaned by running through a fanning mill before it is treated because the solution is not strong enough to kill the disease (fungus) which is inside of bits of straw and chaff. "After treating, it may be well to sow two or three quarts more per acre, as some of the weaker seeds are apt to be killed. Scaly flax seed and seed which has been wet is always very poor for seed. Such seeds harbor the spores of fungi which kill the young plants as soon as the seeds germinate. Cease sowing flax year after year upon the same land. Put at least one cultivated crop and two or more other crops between flax crops. Burn as much of the old straw and stubble which remains upon the ground as pos- sible. Raise your own flax seed, grade it up to the best. Watch for disease areas and notify the station. Thresh your seed, when you can, in your own machine from a patch of strong healthy flax and store it in a clean bin. Keep all the flax straw out of the barnyard, unless it is intended to put all manures through a several years' composting process. I can- not say that this process will be successful in destroying the fungus. It is destructive to most weed seeds and to the spores of many fungi. Avoid the evil effects of deep planting. Much damage is done to the flax crop of the state by too deep plant- ing. The flax wilt disease does more injury to the seedlings when the seed is placed deep in loose soil than when planted shallow. One-half inch to three-fourths inch is the best depth. The seed bed should be of even texture and quite compact." Downy mildew of clovers (Peronospora trifoliorum De Bary). This parasite attacks clovers and its relatives, such as lucerne, etc. The summer spores form on thread branches, similar to those of the downy mildew of mustards and the win- ter spores are also similar to the latter. Summer spore patches are pinkish grey and are found on the stems, leaves and peti- oles. Diseased plants, should be destroyed to prevent the oc- currence of the disease in the following year. Sorghum blight (Bacillus sorglri Burr). This is a bacterial disease of sorghum plants. It appears on the leaves as reddish Minnesota Plant Diseases. 315 spots which are usually elongated to narrow lines. Later they increase to large irregular spots and may then entirely destroy the leaves. Both the sheaths and blades of the leaves are af- fected. The roots are also attacked and it is possible that the bacterium lives over unfavorable seasons in the soil. The bac- terium is usually not found in the stems except in the wounded portions. It is probably found in Minnesota though not yet reported. Land upon which diseased plants have been grown should not be sown to sorghum for a year or two. All diseased plants should be burned. Chapter XIX. Diseases of Garden Crops. Orange- or red-rust of raspberries and blackberries [Gym- noconia inter stitialis (Schlcct.} Leigh.]. This rust is chiefly known on account of the destruction occasioned by the cluster-cup stages, on the raspberries, blackberries and their allies. The cluster-cup stage differs from that of most of our common rusts by the absence of a cluster-cup wall, so that the chains of spores are spread out on the surface of the leaves. These spores are pro- duced in great numbers in early summer and late spring and form what is common- ly known as the orange rust. The rust is produced on the under sur- face of the leaf, and wild and cultivated raspberries, dew- berries and blackberries suffer. The spores fall in a dense orange powder. From golden orange, the lower surface of FIG. 169. — Orange rust of raspberry and blackberry; to the right on a leaf of wild blackberry; to the left a normal unattacked leaflet. Original. Minnesota Plant Diseases. ~>ij the leaf gradually becomes lighter yellow. The sum- mer and winter spores are not so conspicuous and occur on the same host. The fungus threads live permanently in the rasp- berry tissues, so that the destruction of the whole infected plants is necessary. All diseased plants should be dug out and burned. Spray- ing with bordeaux has been suggested to hold the spread of the disease in check. The cluster-cup rust of gooseberry and currant (Aecidium grossulariae Schwn.}. The fungus causing this disease is exceed- ingly abundant on wild gooseberries and currants throughout the state and is also known on cultivated forms. Serious dam- age, however, is seldom reported. The fungus is a rust fungus and is known at present only in its cluster-cup stage. This is found on the leaves of the host plant and the cups are always found on bright, orange-yellow, swollen spots of the leaf. The cups stand on the lower surface and when they open, release the golden-orange powder of spores, which may carry the infec- tion to other plants. The cups are accompanied by very minute pear-shaped capsules, containing spores on the upper surface of the yellow leaf-spots. The openings of these can be seen with the naked eye as small black dots on the upper sur- face of the leaf. These spores do not assist in spreading the disease. It is not known where the summer and winter spores are formed. They probably occur on some species of sedge. In our lack of knowledge of the complete life history of the disease, the only suggested remedy has been the destruction of diseased parts of the plant. Mint rust (Puccinia menthae Pers.}. Mint rust is very abundant on a great many of our wild and cultivated mints. It is said to be very destructive to the latter, where these are cul- tivated on a large scale. The summer and winter spores are most abundant and form small, dark-brown, powdery patches, chiefly on the leaves. These patches, or sori, often occur in such profusion that they completely cover the under surface of the leaves. The cluster-cups are formed, as usual, in the spring or early summer and are of less frequent occurrence. They occur on the same plants. The mycelium passes the winter in the underground stems of the host. The cluster-cup stage has ii8 Minnesota Plant Diseases. \j been reported from a greenhouse in this state where it de- stroyed almost an entire winter crop of mint. The complete destruction of all diseased plants and espe- cially all subterranean portions is necessary. (Fig. 209.) Asparagus rust (Puccinia asparagi DC.). Of recent years this rust of asparagus has become of great importance in the eastern states and in California and will undoubtedly soon be of equal importance in this state. In parts of eastern states aspar- agus culture in whole districts has been ruined by this parasite. The cluster-cup stage is produced on the asparagus plants in the spring but is usually •••••'•JA not conspicuously abundant. After ~ the crops have been harvested, the sum- mer spores appear as | brownish spots on the stems of the host plant. The winter spores are produced later in long, black streaks upon the stem. The rapid spread of the fungus and the tax of the mycelium on FlG. 161 Wintc soores of the asparagus rust. Highiy the nutrition Of the magnified. Microphotograph by E. W. D. Holway. host, greatly enfeebles the plant and the crop of the following season is seriously affected. If no combative measures are used, the fungus gains strength year by year and soon enforces the abandonment of asparagus culture. The winter spores are two-celled and germinate in the usual way in the following spring. Several fungus parasites on the rust plant are known but they do not apparently exercise sufficient destructive in- fluence to be of assistance to the agriculturalist. This is a very serious disease and difficult to combat. It is first of all necessary to remove all badly diseased plants and to burn all infected plant remains in the fall. In badly diseased districts this method will not alone suffice. Moreover, earlv Minnesota Plant Diseases. cutting and burning, injures the asparagus. Ordinary bor- deaux mixtures have been tried but with little success. Resin bordeaux is recommended by the New York Agricultural Ex- periment Station where the rust has been successfully treated with this mixture. The application with ordinary barrel pumps is too laborious and slow, so that it was found necessary to de- vise a special sprayer, the plans and description of which are published in the bulletins of that station. (See N. Y. Ex. Sta. Bull. No. 1 88.) Sulphur has very recently been shown to be quite successful in keeping clown the disease in California. Bean rust [Uroniyces appcndiculatus (P.) Link.]. This is not usually one of the most serious of bean diseases, but may in some localities become a dan- gerous pest. It attacks chief- ly the common garden bean, but has also been reported on other beans. All three spore forms occur on the same host plant. The cluster-cups are yellowish and appear in the late spring. The summer and winter spores appear later in small pustules, about the size of a pinhead. These pustules are light- to dark-red-brown and appear chiefly on the leaf- blades but can also be found on the petioles, stems and even on the pods. The pus- tules are circular in outline and the spore masses of summer and winter spores are powdery. The winter-spore pustules are dark-brown and may finally be- come blackish in color. The winter spores are single-celled and germinate in the usual method for rust winter spores. Certain varieties of bean resist the rust and such should be planted. Infected plants should be destroyed by burning. Bordeaux mixture has also been suggested as a means of hold,- ing the disease in check, but is not in general use. FIG. 162. — Rust of bean. Winter spore clus- ters on the lower surface of a bean leaf. After Clinton. 320 Minnesota Plant Diseases. Onion smut (Urocystis cepulae Frost.). This is a leaf-smut and is due to a fungus somewhat similar to that of the rye smut. The smut masses appear in lines on the foliage leaves and may later appear on the scale leaves of the bulb. The spores are aggregated into true spore-balls, of which the outer spores are sterile and incapable of germination, w.hile the inner are fer- tile and well protected by the outer ones. The infection of the host plant takes place in the seedling stage. Diseased plants should be destroyed. Care should be taken not to plant seed in smut-infected soil, since the smut spores re- tain their power of germination for many years. Care should also be taken to prevent the transference of smutted plants or smut-infected soil from one bed to another. When seeding in infected soil, "apply in the drills per acre one hundred pounds of sulphur thoroughly mixed with fifty pounds of air-slacked lime. Formalin (one pound to thirty gallons water) thorough- ly sprinkled over the seed before covered with the soil, or ap- plied by drip attachment to the seeder, is an efficient remedy. Ground lime, drilled in the land with a fertilizer drill, at the rate of 75 to 125 bushels per acre, is helpful in keeping the trouble in check." (Conn. Ag. Ex. Sta. Bull. No. 142 — 1903.) The currant pore-fungus rot [Pomes rib is (Schum.) Fr.]. This disease of currant bushes is probably not common but has been observed in this state. The fungus mycelium is parasitic in the root of the currant, producing its fruiting bodies at the surface of the ground, particularly around the base of the stem. The affected portions of the root-tissue turn black and the roots, and subsequently the remainder of the currant bushes, are finally killed. The fruiting bodies are dark-yellow-brown, woody, thin, saucer-shaped shelves and live from year to year. The pores are small and line the under surface of the fruiting body. The latter are sometimes six inches in diameter. It is said also to attack gooseberry bushes. All fruiting bodies and infected plant-parts should be re- moved and burned as soon as discovered. The sclerotium disease of cucumbers and other garden plants (Sclerotinia libertiana Fckl.}. The fungus cause of this disease is a sac fungus with a peculiar life history. When the sac spores germinate at the surface of the soil they produce a my- Minnesota Plant Diseases. 321 FIG. 163. — Pore-fungus root rot of currant (Fomes ribis), showing shelf-pore fruiting body at the base of the canes of an attacked currant plant. Original. 21 322 Minnesota Plant Diseases, celium, which feeds in a saprophytic manner upon vegetable debris in the soil. After the mycelium has been strengthened by this saprophytic life it is able to infect living plants. The cucumber seems to suffer considerably but a large assembly of other plants are also subject to the attack of either this or closely allied species of fungi. The mycelium attacks the stem just above the ground and the stem at this point is covered with a fine white mold. The fungus proceeds rapidly up the stem and the latter soon falls and dies. The mycelium now continues to live in the dead tissues and builds up storage organs known as sclerotia. These are small, dark, compact masses of fungus threads in which a great amount of storage material such as fungus starch is deposited. This sclerotium lives through the winter in the dead stem and, in the spring time, produces a cluster of cup-fungus fruiting bodies with long stalks. The in- ner surface of the cup is lined with a palisade of sacs, each con- taining eight spores. The fungus may also attack stored roots and bulbs such as dahlias, turnips and beets and has been known to cause consid- erable damage. Growing lettuce is also subject to attack and the resulting disease is commonly known as drop from the rapid collapse of the host plant. In this common disease the sum- mer spores of the fungus are produced. All diseased plant parts should be collected and burned. It has been recommend- ed that lime be sprinkled on the soil to kill off the saprophytic mycelium from which the infection takes place. The use of fresh manure should be avoided where the disease has once been found. Sterilizing of the soil has also proven successful in controlling the sclerotium disease of lettuce. Drop of lettuce (Sclerotinia libertiana FckL). See Diseases of Greenhouse and Ornamental Plants. Red knot of currants [Ncctria cinnabarina (Todc.} Fr.]. This is not an uncommon disease in Minnesota. It attacks chiefly the currant and often causes the death of the canes. The fruit- ing bodies appear on the dead canes as small red buttons or cushions which break through the bark of the cane. In an at- tacked plant the foliage wilts and the fruit colors prematurely. The fruit clusters of the currant are smaller than normal and the berries fall off early. Sometimes only the central canes of Minnesota Plant Diseases. the bush are killed off. The fungus fruiting cushions at first bear colorless spores, which are pinched off of threads on the top of the cushion in great numbers. The spore sacs are formed in the fall and arise in pear-shaped capsules. The latter are formed as protuberances from the summit of the button and have an apical opening, through which the spores are forced out. The mycelium is perennial in the cane and can be trans- ferred by cuttings. An infected bush may thus be a constant source of infection. Cuttings from plants should therefore be selected from bushes free from the disease. Infection from spores probably takes place only through wounded canes. Wounding of canes should therefore be avoided as far as possi- ble. Diseased plants should be immediately and completely rooted out and destroyed. Strawberry leaf-blight [Spliacrclla fragariac (Tnl.) Sac'c.]. This disease is a verv common one in the state and attacks cer- tain varieties more vigorously than others. It appears on the leaves and the first indication is a spotting of the leaf. The spots are circular and purple in color. As they increase in size the center of each spot becomes whitish and the edge remains purple. On the whitish area appear in early summer minute tufts of fungus threads, which constrict off countless summer spores of exceedingly small size. By means of these the fungus disease may be carried to other plants. The spots are often so numerous that they run together and cover such a considerable portion of the leaf that the latter is rendered useless for starch- making purposes. On the same white spot, later in the season or in the fall after the leaf has fallen, the winter or sac spore is formed. The sacs are produced in very minute, spherical cap- sules which protrude from the spot as tiny black points. They open to the exterior by means of small apertures through which the spores escape. The release of the spores is delayed until the following spring, so that infection by the sac-spore myce- lium does not take place until that time. To check the spread of the fungus spraying with bordeaux has proved beneficial and several applications should be made. The plants should be sprayed just as the leaves unfold, again after the petals fall, and once or twice after the fruit has been picked. Where the disease is serious, a removal of the plants 324 Minnesota Plant Diseases has been recommended, or the plants may be mowed in the fall, removed and burned. Good results have also been obtained by burning over the bed with the aid of a layer of straw. The selection of varieties will also assist in the combating of the dis- ease, as certain varieties are much more susceptible than others. (Fig- 35-) Powdery mildew of strawberry (Sphaerotheca castagnei Lev.}. This disease has not been reported from many localities in the United States but seems to give promise of becoming a destructive disease under favorable conditions. The leaves and fruit are attacked though the former usually suffers most. On the under surface of the leaf the fungus forms the characteristic superficial mildew of this group of fungi and when the summer spores are formed the powdery appearance is noticeable. The leaves curl up and may finally dry up. The winter spores appear in sacs borne in the receptacles (sac capsules) usual for this gi'oup of fungi. The exact identity of the form is not known but it is probably a close relative of the powdery mildew of hops. Powdered sulphur is usually recommended, or spraying with ammoniacal copper carbonate. Powdery mildew of cucumbers (Erysiphe ciclwracearmnDC.'). This disease has been reported as destructive to cucumbers, especially those grown in greenhouses. It is a typical powdery mildew and appears to be identical with the exceedingly com- mon powdery mildew of composites, which appears so abun- dantly on a great variety of our wild plants. The mycelium ap- pears on the leaves or stems of the cucumber as small white spots, which soon produce the mealy powder of summer spores. The spread of the infection may be rapid and the infected spots increase in size, becoming yellow and then brown, and may final- ly destroy the whole leaf or even the entire plant. The winter spores are formed in sacs, found in small black capsules, com- mon in the powdery mildews. A large number of sacs is formed in the capsule and the appendages of the latter are sim- ple and interwoven with the mycelium. When the capsules are formed, the mycelium has become a greyish or dirty white coat on the leaf surface. Minnesota Plant Diseases. 325 Sulphur dusting, spraying with ammoniacal copper carbon- ate, have all given good results. The ground should not be allowed to become infested with the resting spores (winter spores), hence the diseased plant parts should be burned. Powdery mildew of gooseberry [Sphaerotheca mors-uvae (Schwcin.} B. & CJ\. Gooseberries are not infrequently attacked by this destructive disease. The leaves, fruits and shoots are coated with a fine whitish mycelium. Summer and sac spores are produced as is usual in the true powdery mildews, and the sac capsule is in general like that of the rose mildew, though dif- fering, of course, in minor details. There is another powdery mildew (Microsphaera grossu- lariae) which is known to occur on the gooseberry though not as commonly as that described above. It can be distinguished by the many-times forked appendages on the sac-capsule and by the large number of sacs in each capsule. "Spray with potassium sulphide as soon as buds break and repeat about every ten days until end of June." (Conn. Ag. Ex. Sta. Bull. 142 — 1903.) Powdery mildew of hops(Sphaerothcca castagnei Lev.}. This is perhaps identical with the strawberry-leaf powdery mildew, or a biologic form of this species. The mycelium of hop mil- dew, like that of rose mildew, is superficial and forms a whitsh coat on the surface of leaves of hops. It also inhabits mem- bers of the rose, composite and other families. The fungus threads send sucker branches into the epidermal cells withdraw- ing from the latter their nourishment. The sac-capsules are similar also to those of rose mildew. Summer spores are also similarly produced in chains. Where hops is raised in abund- ance the mildew may cause very serious damage. Bordeaux or ammoniacal copper carbonate can be used as a spray. Powdery mildew or blight of roses [Sphaerotheca pannosa (Wallr.) Lev.}. See Diseases of Greenhouse and Ornamental Plants. (See Figs. 203 and 204.) Powdery mildew of vetch and crowfoot [Erysiphe com- munis (Wallr.} Fr.]. This is sometimes found on cultivated plants of the pea family. See Diseases of Wild Plants. 326 Minnesota Plant Diseases. Potato scab (Oospora scabies Tlia.rt.}. Potato scab is an ex- ceedingly common disease of potatoes. The cause has been the subject of some dispute among botanists but it is now gen- erally accepted that the common form of potato scab in Amer- ica is due to a parasitic fungus, while the European scab has a very different cause. The American potato-scab fungus be- longs to the group of "imperfect" fungi and is found amongst the white, loose-spored forms. Scabby potatoes when freshly removed from the soil show a very delicate moldy coating, in which the loose spore-bearing threads are found. The surface of an attacked potato becomes roughened and scabby, hence the common name of the disease. The fungus can remain in the soil for sev- eral years and badly in- fested fields should not be sown to potatoes. Since the fungus is a lurking parasite and gains entrance through the potato skin, it has been found that a treat- ment of the "seed" pota- toes will kill off the scab fungus. Immersion in a solution of one pound of corrosive sublimate to fifty gallons of water for one and one-half hours will free the potatoes from scab providing other precautionary measures are taken. After treatment, the potatoes must be kept free from the disease. They must not, for example, be brought into contact with other diseased potatoes or must not be planted in soil which is badly infested with the scab. A formalin solution may also be used as a steep. This solution is made up of one pound of formalin to thirty gallons of water, and the "seed" potatoes are immersed for about two hours. The corrosive sublimate solution is very poisonous ; potatoes treated by the first method must therefore never be fed to stock. FIG. 164. Potato scab. After Clinton. Minnesota Plant Diseases. 327 Scab of beet. See Potato Scab. Anthracnose of currant and gooseberry [Gloeosporium ribis (Lib.} Mont, ct DCSJH.]. This disease is well known in Minne- sota. The fungus appears on the upper surface of the leaf in very minute black spots which are cushions of fungus threads. These are formed under the epidermis and then burst through, finally producing spores on the surface of the cushion. The fungus is therefore one of the cushion-forming "imperfect" fungi. The spores cling together in gelatinous masses. When the spots are very abundant the leaf turns pale and falls. The whole bush may thus be deprived of its foliage and in conse- quence may be seriously injured. The fruit on such bushes is usually inferior and the crop for the following year may also be damaged. Treatment with bordeaux has been recommended, as follows : "First spraying with bordeaux before leaves ap- pear, the second as the leaves are unfolding, and repeat at in- tervals of ten to fourteen days until the fruit begins to turn." (Conn. Ex. Sta. Bull. 142 — 1903.) Bean anthracnose \Cottetotrichum Kndeinuthianum (Sacc. et Mogn.} Bri. ct Cor.]. Beans are very frequently attacked by an- thracnose. The fungus causing this disease is an imperfect fungus belonging to the cushion-forming group. It attacks the pods and also the leaves but is more commonly found on the former. Blackish spots are formed with purplish edges and these spots enlarge, and when abundant may cover a large part of the pod. The tissue under the spot is sunken so that the fungus-thread cushions, which are formed in the center of the spot, are at the bottom of small sunken areas. These cush- ions bear numerous upright threads, from which spores are pinched off, and between these threads arise sterile, sharp- pointed, dark, spine-like threads, which bristle from the top of the cushion in a formidable manner. Spraying with bordeaux has been recommended and should commence when the plants are small. They should be made at intervals of a few weeks until the pods are ripening. Damp situations should be avoided and all badly diseased plants should be destroyed. The disease can be carried along with the seed so that it is necessary to avoid seed from infected pods. Care must also be taken to avoid planting beans in badly infected fields. 328 Minnesota Plant Diseases. The leaf blight of celery (Ccrcospora apii Fr.). The fungus causing this disease is a loose spored, imperfect fungus. It causes the formation of red- dish to brownish spots on the leaves, which may spread and increase in size until the leaf is seriously injured. The fungus thrives well on plants in dry situations and is particularly effective against young plants. When badly affected the leaf turns yellow and finally brown. Spots may also appear on the stem. The spores arise from upright fungus-threads in the center of the spot and are ar- ranged in a fine, loose, mold- like growth. Shade and moist situations have been recom- mended, but are only partially successful. Spraying will also keep the fungus in check. The spraying should com- mence early and bordeaux may be used at first but the ammo- niacal copper carbonate is used in the later sprayings. The leaf spot of beets (Ccrcospora bcticola Sacc.). This is a common spot disease on the leaves of the beet. The cause of the disease is a loose-spored imperfect fungus. It forms small circular spots on the leaves, often in great abundance. The spots have a purple border and whitish centers, where the loosely arranged threads bearing the spores are found. Spraying with bordeaux mixture has been recommended. Frequent applications should be made throughout the growing season. Black rot of tomato (Macrosporium tomato Cooke). Tlrs fungus attacks chiefly the fruits but is also found on the leaves and stems. It is probably identical with the fungus of early potato blight. It forms on the fruit circular spots, under which FIG. 165.— Aiithracnose of bean. After Hal- sted. Minnesota Plant Diseases. the tissues soften and become discolored. The fungus threads form black, velvety masses in the center of the spot and these masses increase rapidly in size until large mold-like patches are produced. The dark spores are pinched off of the threads which are formed in a loose arrangement on the surface of the fruit. This parasite is a sac fungus of the black fungus group but the sac spores are very uncommon. Bordeaux mixture has proved successful in combating this disease. The first treatment should be given when the flower buds open and should be repeated at intervals of two weeks. Early blight of potatoes (Macrosporium solani Ell. et Mart.). This disease is easily mistaken for the ordinary or "late blight," but has an entirely different cause. It affects early crops and is in general found early in the season. The general symptoms are those of premature ripening of the plants. The leaves turn yellow toward the edge, curl up and finally become dark brown. The entire plant is weakened and may die early, giving the appearance of early ripening. The fungus is similar if not identical with black rot of tomatoes. Vigorous plants are said to withstand the attack, so that careful cultivation has been recommended. Bordeaux mixture applied early in the season is also an effective preventive. The sterile-fungus rot of garden plants (Species of Rhizoc- tonici). All kinds of garden plants are affected by a rot which attacks the roots or lower stem and which frequently causes the death of a great many plants. The classification of this fungus cannot at present be determined, since it has never been found to produce spores. It is therefore called a sterile fungus, though it is of course possible that spores are formed under unusual and rare conditions. The fungus produces tufts of threads on the infected parts of the host plant. These thread tufts are usually brown or blackish. The threads are brown and branch irreg- ularly in forking fashion and often break up into lengths which may germinate in the fashion of spores, but these lengths are not considered real spores. The following list will show some though not all of the plants attacked by this fungus in the United States : bean, beet, carrot, celery, cabbage, cauli- flower, lettuce, potato, radish, rhubarb, ornamental asparagus, china aster, sweet william, coreopsis, and violet. In many cases 33° Minnesota Plant Diseases. this fungus can be shown to be truly parasitic but in others is doubtfully so. It is usually capable of unlimited growth in a saprophytic manner. The elimination of unfavorable conditions of temperature and moisture are recommended. Freshly decaying vegetable matter should be removed. The soil may be limed as an aid but is not an absolute preventive. A complete sterilization of the soil should entirely prevent the disease. Grey mold of lettuce. See Diseases of Greenhouse and Or- namental Plants. White rust of mustards, cabbage, etc. [Albugo candidus (P.) Ktze.]. This is one of the most widely distributed fungi known. It occurs on all kinds of plants belonging to the mustard family on both wild and cultivated forms. It is most commonly found on the wayside weed known as shepherd's purse, but is also found on many other wild mustards. Amongst cultivated plants the following are frequently infected : radishes, horse- radish, cress, cabbage, turnip, water-cress and wall flower. Plants closely related to the mustard, e. g., caper plants, are also known to become infected. The fungus attacks the plants in the seedling stage through the seed leaves. The mycelium very frequently causes abnormal and distorted growths in the host plant and in these regions the summer spores are formed. These are produced in extensive patches which at first have a porcelain-like appearance. Later, by the bursting of the superficial tissue of the host plant, the spores are set free as a white powder, hence the name white rust. The spores are formed in chains and the spore powder is blown by the wind to other plants. The spores require moist con- ditions for germination, and under these conditions break up into tiny swimming spores which scatter the infection by mov- ing about in the drops of water on the leaf. When they come to rest they germinate into a tube which infects the leaf. The winter spores are formed as a result of a breeding act between two swollen organs formed on the fungus threads and are pro- vided with a thick coat. They are produced within, the tissues of the host and are set free in the following spring by the de- cay of the tissues. These winter spores produce swimming spores in a similar manner to the summer spores. Minnesota Plant Diseases. 331 This is not usually of serious importance to crops in this state. Diseased plants should be destroyed. Downy mildew of mustards, cabbage, &e.[Peronosporapara- sitica (P.) DcBy.]. This disease usually accompanies the white rust of the same plants. It is found in general upon the same plants as white rust and often causes deformations of the host. The summer spores are produced on filmy patches of a downy nature and can thus be distinguished from the white rust. They are not produced in chains but in clusters on much- branched threads, which protrude from the leaf of the host and give the downy appearance to the infected regions. The winter spores, which are similar in appearance to those of white rust, do not, however, produce swimming spores, but germinate into an infection tube. For preventives see White Rust of Mustards, etc. The downy mildew of potato. Potato blight \Phytophthora infcstans (Mont.) DcBy.]. This disease has proved an exceed- ingly destructive one both in the United States and in Europe. It was first known in the United States between 1840 and 1845 and was introduced into Europe about 1845, It probably came originally from South America, where it grows on many wild p1ants of the potato family. Shortly after its introduction into Europe, it caused complete failure of the potato crop in many districts. In America it causes most damage in the eastern states and is apparently not so destructive in Minne- sota, though by no means unknown in this state. It may sometimes be found growing on close relatives such as tomato and other members of this family. The parasite has the typical habit of the downy mildews and hence grows best in moist seasons or in low-lying, damp situations. The mycelium is de- structively parasitic and as soon as it is established in the leaves of the host plant causes a diseased condition. The first indication is the appearance of brownish spots, which rapidly grow darker and finally become blackish. The discoloration is often accompanied by a crumpling of the leaves. The diseased leaves finally suffer complete decay and produce an offensive odor. The lower surface of the leaf-spots is seen to have a very delicate downy coat, which increases to a white band around 332 Minnesota Plant Diseases. the border of the spot. Here are produced the spores, which are formed in a manner peculiar to the potato blight and its close relatives. The method of spore formation serves to dis- tinguish these forms from the downy mildew of vines and other downy mildews. The spore-producing threads pinch off spores from their apices and then the thread grows past the spore, shoving the latter to one side. It grows on for a short distance and then produces another spore apically. The threads show somewhat pointed ends. They are, moreover, FIG. 166.— Potato blight. Early stages of the blight on the leaves. After Clinton. usually much branched, so that a miniature bush-like structure is produced and each branch terminates in a spore. These spores, as is true for most of the downy mildews, are in reality spore cases, for when placed in water they later give rise to a large number of swimming spores. When the latter come to rest they germinate into a tube which causes infection of the host plant. As far as is known at present, no winter spores are produced. The mycelium, however, is capable of living in the above ground stems and in the tubers of the potato, and may live in the latter over winter, producing a brown rot of the tubers. In the following spring they can again cause in- fection by growing up into the stem and leaves. It is there- Minnesota Plant Diseases. 333 FIG. 167. — Potato blight. Later stages on the leaves. After Clinton. fore unsafe to use for seed potatoes tubers harvested from an infected crop. "Spray with bordeaux before the trouble appears, about July 7th to loth, and keep vines well covered, es- pecially from the middle of July to the middle of Au- gust. Unless season is very moist three sprayings should suffice. If this treatment is impossible plant early varieties only." (Conn. Ex. Sta. Bull. 142 — 1903-) It has been -claimed by various authors that the bordeaux spray not only destroys the parasite but improves the foliage of the potato as well. Dis- eased plants and tubers should be burned. Wet soil should be avoided, if possible, for infection can take place in the tubers in spring as well as in the leaf. Thick-skinned potatoes have been recommended as more resistant to the fungus than thin- skinned ones so that, for storage in particular, these varieties should be selected. (See also Fig. 39.) Downy mildew of onion (Peronospora schleideni Ung.). The mildew of onions has long been known in Europe where it is much feared. It has now become established in many places in the United States and has appeared in abundance in Wiscon- sin. The fungus, like the other downy mildews, produces sum- mer and winter spores. The former are produced on the leaves upon threads in a manner similar to that in the grape mildew. They give to the leaf a grey to green, moldy appearance and the leaf-gloss appears to be lost. The spores in moist condi- tions produce swimming spores, but are very sensitive to, and easily destroyed by, drying. The winter spores are provided with a thick protective coat. They are very resistant and in the spring following their formation produce swimming spores in a manner common to the downy mildews. The fungus is 334 Minnesota Plant Diseases. very common upon plants raised on previously infected land and in such cases infection is almost certain. The disease spreads rapidly and may cause great damage in a single season. Infected plants should be destroyed to prevent future infec- tions. When a field is badly infected, as when infected plants are left on the field, the rotation of crops becomes necessary. Spraying with bordeaux has given satisfactory results in com- bating this disease. In some cases this has proved injurious to the foliage when used in standard strength. There is also diffi- culty in making the bordeaux adhere to the very glossy surface of the onion leaf. Powdered quicklime (two parts) and sul- phur (one part) has been recommended for checking the dis- ease in the early stages. Spraying with potassium sulphide is also effective. Of chief importance are the avoidance of too damp conditions and too much shade, the removal of infected plant parts and the rotation of crops, if necessary. Downy mildew of cucumber, melon and other gourds [Plas- mopara cnbcnsis (B. & C.) Hitmpf.]. This has proven in certain parts of the United States to be an exceedingly virulent disease and has threatened to completely destroy the pickle crops in those districts. It is not as yet known to be common in Min- nesota, but it will probably appear here in time and the farmer who is employed in the growing of cucumbers or other gourd fruits will do well to know the disease and to keep a sharp look- out for it. It is known to attack cucumbers, muskmelons, pumpkins, warty and winter squash, watermelons and various other gourd fruits. Unlike the powdery mildew of the cu- cumber, it is more common in fields and gardens than in green- houses, but it is not unknown under the latter conditions. It is in many places the chief enemy of cucumber culture. An important feature lies in the fact that it can spread from one host to another. The disease is best recognized by the action upon the foliage, though it is by no means confined to the leaves, but may occur on the stem as well. Infected leaves turn yellow in spots and these yellow spots are bounded by the veins of the leaves and are therefore usually four-sided and angular. They are up to a quarter of an inch across, but by joining with neighboring spots may become much larger. The spots in- Minnesota Plant Diseases. 335 crease in size and number with great rapidity until the whole leaf finally becomes yellow, then dries up and shrivels. The oldest leaves, i. e., those nearest the hill, are usually first affect- ed and then the disease travels toward the tip of the host plant with great speed. The spread of the disease is particularly fa- vored by hot weather and by a damp atmosphere. The yield of cucumbers is quickly affected, because the whole plant is rapidly weakened or may be entirely destroyed. On the older plants FIG. 108.— Downy mildew of muskmelon. Blighted vine i one finds on close examination a fine down, sometimes of a pur- plish tinge, covering the under side of the leaf. This is caused by the fungus threads, which bear the summer spores. The latter are produced in a similar manner to those of the downy mildew of grapes and are carried by the wind to other leaves and plants. Here they form a large number of swimming spores, which further scatter the infection under proper condi- toins of moisture. The swimming spores germinate into infec- tion tubes, and thus establish a mycelium within the leaf. This fungus has not been known to produce winter spores, — prob- ably does, however, under rare conditions. The method of wintering over is therefore at present unknown. It undoubt- edly does, nevertheless, pass the winter safely, as has been shown by the experience of cucumber growers in many places. 336 Minnesota Plant Diseases. "Repeated sprayings with bordeaux about every ten days during a season, beginning at least by the middle of July, is useful in keeping this disease in check." The number of spray- ings is dependent on the season. In very wet seasons more may be necessary. If the under surfaces of the leaf can be sprayed, the results will be most successful, but great gain is possible by the ordinary method of spraying. Downy mildew of beans, peas, etc. (Phytophthora phaseoli ThaxtJ). A downy mildew frequently attacks cultivated beans and closely related plants and may create a very serious amount FIG. 169. — Downy mildew of muskmelon, showing the under surface of an attacked leaf. After Clinton. of damage. The summer spores are produced in a similar man- ner to the blight of potatoes. The young stems, leaves and pods are attacked. The downy patches on the pods are usually dense, woolly growths, whitish in color, while those on the stems and leaves are less dense. As with most downy mildews, moist seasons or moist situations favor the growth of the dis- ease. Diseased plants should be burned to prevent the recurrence in following seasons. "As the fungus usually appears first and most vigorously in low, moist places, the land used should be high or well-drained. Spraying, beginning with bordeaux and Minnesota Plant Diseases. 337 ending with ammoniacal solution of copper carbonate and re- peated every ten to fourteen days from the last of June until the first part of September, is helpful in keeping- this trouble in check." (Conn. Ex. Sta. Bull. 142 — 1903.) This disease is known in eastern states but has not been re- ported from Minnesota. FIG. 170. — Downy mildew of muskmelon. Under surface of an attacked leaf. After F. C. Stewart. Downy mildew of lettuce (Bremia lactucae RegeL). Lettuce in gardens and particularly in greenhouses is attacked by a downy mildew. The spore patches form filmy, grey, mold-like growths on the lower surfaces of the leaves. The spores are borne on much branched threads which terminate in four or five short stalks arising from the rim of a saucer-like expansion. At the ends of these stalks the spores are produced. The fungus 22 Minnesota Plant Diseases. FIG. 171.— Downy mildew of melons and cucumbers. 1. A spore-bearing thread; sp. young spores; 2, 2' and 2", mature spores of the ordinary form. 3. Spore-bearing thread emerging from an air-pore on a leaf. 4. A cluster of spore-bearing threads taken from a cucumber leaf in dry weather, t, unusual types of spore-bearing threads and spores. 6. A short stalked spore from a muskmelon leaf. 7. Cells of a cucumber leaf with the fungus mycelium between them; sucker threads h, h' and h". 8. An unusual type of spore from the cucumber. 9. A very large pear-shaped spore of unusual occurrence. Highly magnified. 7. After Humphrey; all of the others after F. C. Stewart. Minnesota Plant Diseases. 339 thrives best in a moist atmosphere and damp situations, hence is often luxuriant in greenhouses. Infected plants are stunted and turn pale yellowish in color. "This disease is kept in check by subirrigation or care in watering and ventilating to keep plants and atmosphere as free from moisture as is consistent with good growth." (Conn. Ex. Sta. Bull. 142 — 1903.) It has been recommended that infected frames and houses be abandoned for lettuce culture at least for a time. The downy mildew of beets (Peronospora schachtii Fckl.). This disease may prove a serious pest in the raising of beets. The fungus attacks chiefly the inner leaves and in seedling plants may cause the death of the plant. The spore patches are on the under sides of the inner leaves and are greyish, mold- like patches. The fungus threads are said to be able to live through the winter in the roots. The infected plants should be burned. Rotation of crops has been recommended in order to give the mycelium in the roots a chance to die out, The downy mildew of spinach [Peronospora cffusa (Grev.) Rabh.]. Spinach and the other plants of the goosefoot family are frequently attacked by a downy mildew which may cause serious damage. It is also found on wild plants of the same, family. The mold patches of summer spores are found on the lower surface of the leaf and are greyish lilac in color. The winter spores are similar to those of downy mildew of clover. The diseased plant should be burned to prevent the spread of the disease and its recurrence in the following year. Downy mildew of clovers. See Diseases of Field and Forage Crops. Downy mildew of violet (Peronospora violae DeBy.}. See Diseases of Greenhouse and Ornamental Plants. Damping-off of seedlings (Pythium debaryanum Hesse.). See Diseases of Greenhouse and Ornamental Plants. The seedling disease of cabbages [Olpidiumbrassicae (Wor.} Dang.']. This disease is probably not serious in Minnesota. It attacks seedling cabbages and causes a dropping of the plant by the death of the stem. The fungus belongs to a very low or- der of algal fungi and consists of a single cell which invades the 340 Minnesota Plant Diseases, host plant, living in one cell of the host. When it forms spores it develops a long tube, which reaches to the surface of the host plant and throws out spores, which are provided with swimming lashes and by means of these swim in raindrops or in the dew. The swimming spores come to rest and invade the same or other plants. A thick-coated, resting winter-spore is produced inside of the host and this may carry the plant over to the fol- lowing year. Diseased plants should therefore be burned and cabbages should not be planted in beds in which the disease has been serious. As the fungus is a water-loving plant, the seed beds should be well ventilated and kept as dry as possible. Too moist atmospheres should be avoided. Wet rot of potato (Species of Bacillus). Wet rot is a well known bacterial disease. The bacteria enter the potato through wounds or through the ventilating holes in the skin (cork), and when once inside, they commence the de- \ • struction of the contents M • , JPokflHB of the tuber. Large cav- ities appear in the tuber containing a fluid mass, with the potato starch grains still intact. The tuber soon becomes soft and the entire center is filled with a putrescent mass, from which the common name of wet rot is derived. This fluid mass is at first acid, on account of the formation of carbonic acid gas, and the acid of rancid butter. When, later, the decomposition has proceeded still further, am- monia gas and other complex organic compounds are formed which give to it an alkaline reaction. FIG. 172. — Bacterial rot of potato. After Clinton. Minnesota Plant Diseases. -,*l Rotation of crops has been suggested to prevent a recur- rence of the disease. Wilt of cucurbits (Bacillus tracheiphilus Sm.\ Squash, muskmelons, cucumbers and their relatives are attacked. The existence of this disease has not yet been reported from Min- nesota but is well known in eastern states. The disease is caused by bacteria which gain entrance chiefly through wounds in the stem or leaf. These wounds are often caused by insects. The bacteria immediately seek out the water-conducting tis- sues and settle there in such great numbers that the flow of TiG. 173. — Bacterial wilt of squash. After Clinton. water is impeded. The result is a wilting of the plants and death usually follows. This disease is of interest, in that it shows an unhealthy condition in the host plant, induced not by a directly destructive action of the disease-causing organ- ism, but by the interference with the normal life processes of the plant, i. e., the obstruction of the water-conduction current. The sprays which are used for downy mildew and anthrac- nose of cucurbits will prevent this disease. Rotation of crops 342 Minnesota Plant Diseases. has also been recommended but is an uncertain aid and is doubtfully of use. Bean leaf blight(Pseudomonas phaseoli Smith). This disease is of bacterial origin. It has not been reported from Minne- sota but is well known in the eastern United States. It causes a brown tipping of the leaves or dead spots in the leaf. The entire leaf may die. Bean insects, irrigation and mulching are said to have a tendency to increase the disease and certain vari- eties are more susceptible than others. Black rot of £abb%g£(Pseudomonas campestris Smith). This is a bacterial disease and causes a rotting of the plant. Cab- bage and a large number of related plants are affected. The FIG. 174.— Black rot of cabbage. A badly infested field. After H. L. Russell. following list of plants has been reported as sufferers from this rot: cauliflower, kohl rabi, kale, brussel sprouts, broccoli, col- lards, turnips, rutabagas, winter radish and still others. Ruta- bagas and their allies are not so commonly nor so severely at- tacked as the cabbage group. The effect of the disease is first seen at the edge of the leaf. The lower leaves are most commonly invaded but all of the leaves of a head may be attacked at once. The bacteria work downward along the veins of the leaf to the stem of the plant. The invaded veins turn black. From the stem the bac- teria spread outward again with great rapidity. The attacked Minnesota Plant Diseases. 343 FIG. 175. Black rot of cabbage. Artificial infection of cabbage plants. The plants in the center (2), and on the right (1), were inoculated six weeks previously with bacteria. The plant on the left (3) was not inoculated and is therefore unaffected. After H. L. Russell. leaves wilt, turn yellow and finally dry up, when they become somewhat papery in appearance. The disease may appear in stored cabbage in which the heads may be entirely destroyed. Other rots assist in transforming the diseased heads into a rotting, bad smelling mass. Cab- bage for storage should therefore be carefully inspected and where any blackened veins in the leaves show should be rejected. The bacterium gains entrance either through wounds or through the water-pores at the edge of the leaf, weather assists in the spread of the disease. Refuse matter should be removed from the field. Rotation of crops will assist in ridding, in part at least, the soil of the disease. Low, damp soils should be avoided and if irrigation i's practiced reduction of moisture will prevent the formation of water drops at the water-pores on the leaves, and thus reduce the number of chances of infection. Diseased plants can read- ily be detected by breaking off the lower leaves and examining the stalk. If the fibres of the leaf-stalk are blackened, the plant is diseased and should be rooted out and entirely destroyed. FIG. 176.— B lack rot of cabbage. Bacteria highly magnified. After H. L. Russell. Rainy, moist 344 Minnesota Plant Diseases. Allowing these plants to remain on the field only increases the danger. It has been found possible and profitable to attempt FIG. 177. — Black rot of cabbage. Cabbage heads, apparently sound, are attacked by the rot. The progress of the disease is seen in the blackened parts of the stems and leaves. After H. L. Russell. a control of the disease in its early stages by a close inspection of the young plants and by picking off the infected leaves. FIG. 178.— Black rot of cabbage. A cabbage leaf showing the manner of infection. Dis- eased area (B) unshaded except the blackened meshes of veinlets. A. A hole eaten by insects. The disease was introducd at this point and spread backward to the main rib. C. Blackened veinlets affected by the disease. D. Water pores of the cabbage leaf through which the disease germs gain a foothold, producing marginal infection. After H. L. Russell. Minnesota Plant Diseases. 345 Club-root of cabbage, radish, turnip and other cruciferous plants (Plasmodiophora brassicae War.}. This disease is not un- common in Minnesota but the exact extent of its distribution is not known. The cause of the disease is not a true fungus but is a slime mold or fungus animal. It forms no fungus threads but produces spores somewhat similar to those of the true fungi. The spores gain entrance to the host plant, usually in the root region though the parasite may also exist in the leaf. FIG. 179. — Club-root of turnips. 1. Strap-leaf. 2. Aberdeen. 3. Rutabaga. 4. Snowball. 5. Golden Ball. 6. Cowhorn. 7. Kashmyr. After Halsted. It lives within the host in a truly parasitic manner, destroying the cells in which it dwells. It causes, however, great stimula- tion of the tissues of the host, so that the latter produces wart- like growths on its roots. The roots, moreover, become much distorted, hence the common name of club root. The host plant is much weakened by the attack and usually fails to head out. The roots soon decay and thus the animal organisms, which have already formed great numbers of spores, return to 346 Minnesota Plant Diseases. the soil. Cabbages, radishes, turnips and even common weeds of the mustard family, such as shepherd's purse, when planted in such infected soil, will almost certainly become infected. Even the transferrence of soil from such an infected field to an uninfected one, as by clinging to wagon wheels or farm imple- ments may carry infection with it. Manure from cows fed with clubbed roots will easily infect crops. No entirely successful treatment of club root is known. A number of varieties of turnips have been tested and the ruta- baga was found most susceptible. In general, it seems that those turnips with branching and deeply seated roots are most susceptible, while those that do not penetrate deeply and which are not much branched are least affected. Experi- ments also seem to indicate that buckwheat grown in tur- nip land has a favorable effect on the resistance to club root. In general, infected fields should not be used for the same crop — or for any plants of the mustard family — for several years, as the slime mold seems to be able to re- tain its vitality at least for two or three years. The infection of new fields must be carefully avQ'K\^ by preventing the transference of soil or refuse from the infected fields to other plots. The application of a coating of lime to the soil- in the proportion of seventy-five bushels to the acre has been tested and has given very satisfac- tory results. Weeds of the mustard family must be carefully held in check. FIG. ISO.-Club root^of cabbage. After Clin- Chapter XX. Diseases of Orchards and Vineyards. JS Orchards* General treatment of apple orchards. The following has been recommended as a general treatment for apple orchards to keep out common fungus and insect pests. (Connecticut Agricultural Experiment Station Bulletin No. 142.) "i. Spray with copper sulphate solution just before buds start, for Bitter Rot, Black Rot and Scab. This treatment is often omitted. 2. Spray unfolding leaves with Paris Green or Lead Ar- senate in Bordeaux for Bud Moth and Apple Scab. 3. Spray with same as soon as blossoms fall for Codling Moth, Curculio, Canker Worm, Tent Caterpillar, Scab and Sooty Blotch. If badly infected with Sooty Blotch or Scab, spray with Bordeaux mixture ten days later and for Sooty Blotch follow with further spraying. San Jose Scale, Bark Lice and Borers need other treat- ment." Leaf rust of apples and pears. Cedar apples of red cedar (Gymnosporangium macropus Link and Gymnosporangium globosuui Far/.). One very commonly finds on the under sur- face of the leaves of our apple trees large yellow spots, upon which are produced, in spring and early summer, long cluster- cups with beak- or horn-like tops. The leaves are often swol- len in the region of these spots and almost no leaf-green is present. The spots frequently occur in sufficient numbers to completely cover many of the leaves and in this case very seri- ously injure the foliage, and consequently considerably impair the strength of the tree. In the cluster-cups are produced the cluster-cup spores. These spores infect young ^twigs of the red cedar, which soon swell up, forming a ball-like growth which is known as a "cedar apple." 348 Minnesota Plant Diseases. The fungus passes the winter in this diseased portion of the cedar and in the following year the winter spores are produced in early spring. They are formed in a large number of cone- shaped groups arising from little saucer-like depressions, scat- tered all over the surface of the cedar apple. Each spore is provided with a long stalk which swells up in rainy \veather. Since the winter spores are produced in large numbers there are formed long (G. macropus) or short (G. globosum) beak- like, gelatinous masses with a bright, orange-brown coating of FIG. 181. — Cedar apples of red cedar. 1. Showing the swollen branches of the cedar with the winter spore gelatine masses removed (Gymnosporangium globosum). 2. Cedar apple of the same fungus with the gelatinous masses of winter spores. 3. Cedar apples caused by another rust fungus (Gymnosporangium macropus), showing masses of winter spores. 4. Same as 3, but larger specimen. Original. spores. The cedar apples are therefore very conspicuous in wet weather. Some cedar apples (G. globosum) produce win- ter spores for several seasons in succession while the others (G. macropus) produce spores only one season and then die. The winter spores grow out immediately, while still in the gelatinous mass, and produce a number of tiny spores (spo- Minnesota Plant Diseases. 349 ridia), which are caught up by the wind and carried to an apple tree or thorn tree. Here infection takes place on the leaves of the host, where the cluster-cups are soon again produced. Fruit tree culture is often seriously damaged by this apple rust, and the disease may become epidemic over considerable areas. Since cedar trees are a harbor for the fungus, these trees should be carefully watched and removed if necessary. At any rate, branches bear- ing cedar apples should be prompt- ly r e m o v e d and burned. It has also been recommended that diseased leaves and badly infected branches of the ap- ple tree be burned, and that the entire tree be destroyed if badly rusted. Spray- ing has been recommended, but is considered by many to be of doubtful value. Bordeaux is used, and the first spray is given just as the leaves expand and the second a few weeks later. A third is recommended in very rainy seasons. As dif- ferent apple varieties vary in their power of resistance to this rust, resistant varieties may be selected where damage from this rust is very great. The two following diseases produce leaf rusts of apple very similar to the above. Club rust of juniper [Gymnosporangium clavariaeforme (Jcq.) RccsJ]. Another disease, similar in its effects to those of the cedar apple and birds'-nest rust of red cedar, is a rust which attacks our common juniper bushes. An attacked branch swells up into a club-shaped body, often of considerable length. From the surfaces arise, in early spring, small, yellow- ish, club-shaped or cone-shaped groups of winter spores, which swell up in moist weather. Very small spores (sporidia) are produced in a similar manner to the cedar apple and these FIG. 182. — 'Rust of apple leaves. Cluster-cup stage of a cedar apple fungus. After Clinton. 35° Minnesota Plant Diseases. infect the leaves of thorns or apples, where the cluster-cups are formed, also in a similar manner to the above-mentioned rusts. The disease may be dangerous to both ornamental junipers and to orchard apple trees. The preventive measures are similar to those of the leaf- rust of apples produced by the cedar-apples of red cedar. The birds'-nest rust of red cedar (Gymno sporangium nidus- avis Thaxt.}. This is a rust disease similar to that of the cedar- apple of red cedar. When this fungus attacks the red cedar an enormous number of short branches are formed. They are densely bunched together and look like a miniature tree perched on the limb of the cedar tree. This bush-like growth is known as a witches'-broom. At a distance it is not unlike a very large birds'-nest in appearance. On examining the branches of the broom, one sees that the leaves are larger and stand out at a greater angle from the branch than do the leaves on the normal branches; they are also very sharp-pointed and the general habit of the branch is more similar to that of the common juniper tree. Near the base of the leaves in the dis- eased portions of the cedar are found small, brownish, gelatin- ous cushions of the winter spores. These appear at the end of April. The cushions, just as do the beak-like processes of the cedar apples, swell up in wet weather and shrivel up again when dry. Under moist conditions the winter spores germi- nate and produce tiny spores (sporidia), which are carried by the wind to june-berry bushes or apple trees. Here the fungus again develops a mycelium and causes a rust disease which is very difficult to distinguish from that caused on the same plant by the cedar-apple rust. The preventive measures are similar to those recommended for cedar-apples of red cedar and their leaf-rust of apples. (Fig. 26.) Plum leaf rust (Puccinia pruni Pers.\ On the leaves of many of our wild cherries and also on those of cultivated plums, cherries, etc., is often produced a rust known as plum-leaf rust. Only summer and winter spores are produced and they occur in groups or sori on the under surface of the leaf. The sum- mer spores are light brown or reddish and the winter spores are darker. The spores arise in small, yellowish spots on the Minnesota Plant Diseases. leaf and these spots often occur in sufficient numbers to con- siderably damage the plant. The winter spores are two-celled. Spraying with dilute bordeaux has been recom- mended just as the buds are opening and the leaves are expanding, and at in- tervals later. The fallen leaves should be burned. Apple scab [Vcnturia ' pomi (Fr.) Whit.]. Ap- ple scab is by far the most serious disease of apples. The fungus first appears in early summer on the leaves of the apple tree as light, greyish, Circular FIG. 1S3.— Apple scab on the frait After Clii spots which spread rapidly, often combining with neighbor- ing spots to cover large areas of the leaf. The spots later _ turn olive green and finally black. The surface is covered with up- right threads from which the s u m m e r spores are thrown off. These spores rap- ily increase the spread of the fun- gus from leaf to leaf and tree to tree. The spots are frequently so large and nu- merous that the FIG. 184.— Apple scab on the fruit. After Longyear. JeaVCS b C C O m C considerably distorted and are often shed. Whole trees may in this way be stripped of their leaves. This sometimes happens un- 352 Minnesota Plant Diseases. cler conditions favorable to the fungus and such conditions are realized in cold damp summers. The shedding of the leaves, of course, impoverishes the tree not only for one sum- mer, but may weaken it for several successive years. The fungus also attacks the fruit and forms here even more characteristic spots than on the leaf. The fruit spots are dark brown to black, lined with a whitish rim, and are scab-like in appearance. They are usually not over one-half inch in diameter and are more abundant toward the further end of the fruit, though they may occur anywhere on the latter. When abundant the scabs may deform and dwarf the fruit and they always disfigure it, so that its market value is lowered. When the young fruit is seriously attacked the whole fruit may fall. In ad- dition to these injuries, the attacked portions of the fruit become hard and often crack open, allowing the apple to dry out. The cracks also open the way to the soft rots, which soon destroy the apple. The fungus lives through the winter in the sac-spore cap- sule stage. The sacs each enclose eight spores, and are contained in a pored capsule which is formed in the tissues of the apple plant and bursts out at the surface at maturity, ejecting its spores through a pore opening to the exterior. These sac spores are thrown out in the spring, are carried to the lower branches of adjacent trees and here cause the first infection in the spring. In combating this disease a number of recommendations have been made. The disease can be very successfully fought by means of spraying with bordeaux. Several sprayings are usu- ally necessary. A winter spray, with strong copper sulphate, be- fore the buds open should be applied. This should be followed by bordeaux just before blossoming and again just after blos- soming, and two or three other sprayings at intervals of two or three weeks. The number of sprayings must be governed by the amount of rainfall and coolness of the season. Good ventila- tion and spacing of trees and proper pruning will aid in avoid- ing conditions favorable to the fungus growth. The fallen FIG. 185. — Ap- ple scab on a twig. After Clinton. Minnesota Plant Diseases. 35: leaves, where the disease has been prevalent, should be collected and burned, or plowed under, to prevent the formation of spores in the following season. Certain varieties of apples are also known to be more resistant than others toward this disease and a proper selection may aid in combating the fungus. Soft rots of fruits (Penccillium, Mncor, etc.). These rots include some so-called ripe rots and storage rots. The soft rots are due to various fungus growths. They are, in general, molds e;ther of the black or blue mold groups. The habits of these FIG. 180. — Apple scab on the leaf. After Longyear. fungi have already been pointed out in previous chapters. They are amateurs in the ways of parasitism, for they need not only assistance in gaining entrance to the host, but they are capable also of successfully attacking only those parts which are in a resting or dormant condition. The protoplasm of such plant parts, as has already been pointed out, approaches the proteid condition of dead plant debris. Ripe fruits of almost all kinds suffer from these rots. The rots are most destructive in moist warm conditions. 354 Minnesota Plant Diseases. let D r FIG. 187.— Spores of the apple scab fungus. A. Portion of a section through a scab spot on an apple; b, fungus threads spreading under and lifting the cuticle; a and c, partly disorganized cells of the apple; e, healthy cells of the apple. B. Two spore-bearing stalks giving rise to summer spores. C. Spores germinating. D. Portion of a section through an affected leaf of an apple which has lain on the ground over winter and has given rise to the winter spore stage of the disease; g, spore-case containing a bundle of spore-sacs. E. Two spore-sacs, more highly magnified, each containing eight two- celled winter spores, three of which are shown at F. All highly magnified. After Longyear. Minnesota Plant Diseases. -255 Among these molds the blue (or green) mold is perhaps the most common. (See Chapter IX.) So common are the spores of these fungi in the atmosphere that one can find them at all times of the year, often in great abundance, everywhere. An- other common soft-rot of fruits is found in certain kinds of black mold. (See Chapter VIII.) The effect of these rots is a rapid softening of the affected parts of the fruit and, as the fungus spreads, the fruit is finally entirely softened and rendered worthless. The fungi gain entrance to the fruit chiefly through wounds in the skin. Cracks in the skin, such as those caused FIG. 188. — Blue mold soft rot of apple. After L. F. Kinney. % by apple scab, or holes formed by insects, or bruises and cuts obtained in picking, packing and storing, all contribute to the ease of entrance of the fungus. The prevention of ripe-rots is possible to a certain extent by avoiding those conditions favorable to the entrance and growth of the fungi. Warm moist atmospheres should be avoided, hence cold storage of fruits is desirable. Spraying may reduce other diseases, such as scab, and in this way prevent the ripe rots which usually follow such diseases. The spraying on the tree is not, of course, directly beneficial against the ripe-rot, since the 356 Minnesota Plant Diseases. latter are largely store-house diseases. Experiments in formalin treatment and with other chemicals have been unsuccessful. Good ventilation of the stored fruit and a frequent sorting to remove the rotted fruits, thereby diminishing the chances for infection from the spores which are formed on these fruits, are also recom- mended. Any damage, such as bruising or cracking the fruit skin, is to be avoided in all processes of handling the fruit. (See Fig. i.) Bitter rot or ripe rot of apples [Gloincrclla rufomaculans (Berk.) Sp. von SchrJ]. This is also known simply as apple rot. It attacks apples before they are ripe, and also apples in storage ; FIG. 189. — Blue mold soft rot of apple. Accessory spores of the fungus. Highly mag- nified. After L. F. Kinney. it is a very destructive parasite. The parasite is one of the burnt- wood fungi, and it is the summer-spore stage that is the most conspicuous and the form which causes most damage. Where the fungus attacks the fruit, a small brownish red spot appears and increases in size until a considerable area of the apple is in- volved. The spot becomes somewhat sunken, is soft, and the apple underneath has a bitter taste. On the surface of the spot arise usually in well-defined circles the summer-spore masses Minnesota Plant Diseases. 357 which are small, black cushions formed under the skin of the apple. When the spores are ripe the skin is ruptured, and the spores issue in a long cylindrical gelatinous mass which is some- what spirally twisted. Rainwater dissolves the spores apart, and the latter are washed to other fruits, again causing infec- tion. The winter or sac spores are formed in small black cap- sules which are produced in the cankers on the twigs. These cankers are usually found at the bases of infected fruits. The m y c e 1 i u m and winter spores preserve the fungus through the winter. The my- celium, which produces the winter spores, can apparently live saprophytically. Decayed fruit, whether in storage or in the orchard, should be destroyed. Diseased twigs should also be pruned back and destroyed. Spraying with bordeaux mixture begin- nd continued frequently in the growing season, will hold the disease in check. Ammoniacal copper carbonate should be substituted for the bordeaux as the fruit approaches maturity. Potassium sulphide has also been used to advantage. Brown rot of apples. See Brown Rot of Plums (this chapter). Brown rot of p\um[Sclerotiiiia fructigcna. (P.) ScJirt.]. This is a very common disease of plums and may also attack cherries and apples, though the latter rather rarely. In states where the peach is grown, this fruit suffers most of all from the bro\vn rot. The fungus attacks the fruit at about the beginning of the ripen- ing period, but may also extend to the twigs, leaves and flowers. The attacked portions of the fruit turn brownish, forming brown spots which are soft and rapidly grow in size. On these spots arise the summer spores in small clusters which are arranged in circles in the spot. The spores are formed in chains, like strings FIG. 190.— Bitter rot of apple. After Clinton. ning with a winter sprayinp-. 358 Minnesota Plant Diseases. of beads. This summer-spore was formerly known as a loose- spored "imperfect" fungus. The winter spores, however, are now known. Sclerotia or storage organs, formed from densely woven fungus threads, are sometimes produced in the fruit. In the following spring, these sclerotia send up a cup fungus fruit- ing body with a long stalk, and on the inner surface of the cup is formed the layer of spore-sacs. The latter each contain eight spores. These spores probably cause infection in the spring. Attacked fruit falls to the ground or may remain attached to the tree and becomes mummified, producing then an enormous num- ber of spores. These fruit mummies, moreover, may persist through the winter and continue to* produce spores in the follow- ing spring. It is therefore important that all decaying and rot- ting fruit, whether on the tree or ground, be gathered and burned. Affected twigs should also be pruned and burned. A winter spray has been suggested and spring and summer sprays with bordeaux have proved beneficial. In addition to the winter spray the following applications have been recommended : with bordeaux (i), just as the leaves begin to unfold; (2), just after the petals fall; (3), after the fruit sets, and with potassium sul- phide as the fruit begins to ripen. Black knot of plum and cherry [Plowrightia morbosa. (Schw.) Sacc.]. This is a very common disease of our wild cherries and is also common on wild and cultivated plums. The disease de- rives its name from the black charcoal-like knots in the branches of the tree. These knots are caused by the threads of the fungus which inhabit the branches at the knotted points. The fungus gains entrance, perhaps, through a crack or wound and imme- diately causes a stimulation of the tissues, so that a large, soft mass arises, which contains but a small amount of hard woody tissue. This enlarged portion of the branch splits off its outer cork layer and exposes a cushion of densely wefted fungus threads. The cushion is at first yellowish-brown to yellowish- green and turns finally to an olive or dark yellow-brown color. This surface is at first covered with the summer spores which are borne on short upright threads and are capable of causing infec- tion during the same season in which they are formed. Later in the year the knotted portion of the branch turns black and char- coal-like and the surface is then covered with very fine, pimply Minnesota Plant Diseases. 359 protuberances, each of which has an opening at its apex. These openings communicate with the pear-shaped cavities of the cap- sules, which contain the numerous spore-sacs, each bearing eight spores. These are the winter spores and are capable of causing infection during the year following their formation. The fungus FIG. 191.— Black knot of wild cherry, showing various stages in the development of the knots. Original. mycelium may also live over the winter in the tissues of the host and grows from year to year. The ultimate effect of the black knot on a branch is to kill off the entire branch above the knot. When a knot works downward to another branch the latter will also soon be killed. 36o Minnesota Plant Diseases. The fungus can be held in check by a persistent pruning off of the knots. Such a pruning prevents the spread of the myce- lium in the tissues of the host. The knots should be immediately FIG. 192. — Powdery mildew of plums and cherries. 1. Cherry leaf. 2. S.)ore-sac capsule showing the thread appendages with peculiar forking ends. 3. Spore-sacs, each with eight spores. 4. Very highly magnified soores. 5. A chain of summer spores. 6. Two summer spores germinating. All except 1, highly magnified. After Ellis. burned. Care should be taken to prevent a prevalence of the knots amongst wild cherries and plums in the neighborhood of the orchard. Spraying with bordeaux would probably assist in preventing a spread of the disease. Minnesota Plant Diseases. ^6r Powdery mildew of apple [Podosfhacra Icncotricha (E. and F..) Salmon]. This mildew attacks apples, pears, thorns and juneberries. It affects chiefly the seedling plants by injuring the leaves. It forms a fine, whitish, powdery mycelium on the sur- face of the leaves. The small black capsules appear in late sum- mer. Summer spores are produced in the manner usual for the powdery mildews. The small, black sac-capsules are produced in late summer. They are provided with appendages, which form a crown on the summit. The appendages are branched several times in a forking manner. The capsules, when broken open, are seen to contain each a single spherical sac, enclosing about eight spores. Spray seedlings with bordeaux or amm;>niacal solution of copper carbonate shortly after the buds have opened and at inter- vals of ten to twelve days for two months. Powdery mildew of plums and cherries \Podosphaera tridac- tyla (JTal!.} DcBy.]. This mildew attacks leaves of plums and cherries. It is found chiefly on young plants. It forms a fine mycelium on the surface of the leaves. The small, black fruit- ing-bodies appear in the fall. These sac-spore capsules are pro- vided with appendages which* resemble those of the powdery mildew of apples. Each capsule contains a single sac with eight spores. For preventives see Powdery Mildew of Apple. Plum pockets (Exoascus pruni FckL). Plum pockets are very familiar objects to all raisers of plum trees. Cherries are also affected by a similar disease. In this disease the fruit is peculiarly enlarged to considerably more than its natural size and is at first yellowish, becoming grey as a coat of spores form on the surface. The diseased fruit has no stone, the entire fruit wall being so-ft. The mycelium permeates the tissue of the pocket and forms spores in sacs on the surface. The mycelium may live over the winter in the twigs of the plants, so that a plant part once infected may produce pockets yearly. This yearly pro- duction of pockets does not always take place, but they may ap- pear only every other year. The disease does not seem to spread with great ease, for it has been observed that trees neighboring on a diseased one may remain free from pockets for a long time. The spores are borne in elongated sacs which are arranged in £\JA Minnesota Plant Diseases. palisade fashion on the surface of the pocket. Each sac contains about eight spores, which on germination may directly cause in- fection of a host plant. The fungus of this disease is very closely related to the peach leaf-curl fungus and to others forming witches'-broom on birch, alder and cherry trees. It is a sac- fungus with an arrangement of sacs similar to that in the true cup fungi, but has no true cup, since the sacs occur directly on the tissues of the host. FIG. 193. — Plum pockets. These plums are devoid of stones and bear the fungus spores on their surfaces. Photograph by H. Cuzner. The only known effective remedy for plum pockets is the pruning back of the affected parts, so as to remove the fungus mycelium. The pruning must in some cases be quite severe. Of course all pockets must be removed and destroyed, as should all affected parts. It is also advisable not to use the parts of any in- fected tree for grafting purposes, since the fungus mycelium may be transferred with the graft. It has been suggested that the treatment which is successful in combating the leaf-curl of peach may also prove successful here. This consists in spraying with bordeaux when the buds are swelling and again with bordeaux, just before the petals fall. (See also- Fig. 49.) Minnesota Plant Diseases. 363 Witches'-broom of cherries [Exoascus cerasi (Fckl.) Sad.]. One not infrequently meets with wild cherry trees which have the peculiar disease known as witches'-broom. On account of the abnormally large number of branches developed in the af- fected part of the tree, a bush-like object is produced which looks not unlike some foreign shrub, parasitic on the cherry tree. In this broomed portion the mycelium of the fungus, which is a close relative of the fungi of plum pockets and peach leaf-curl, may be found. This mycelium is perennial. The leaves may be considerably distorted, resembling curl, and over the surface of these leaves the spores are formed in sacs. These sacs are arranged in a palisade on the surface and give to the latter a greyish-white appearance. There are about eight spores in each sac. They germinate directly to an infection tube. The broomed portions should be removed and burned. Plum scab (Cladosporium carpophilum Thiim.). This is an imperfect fungus. Many of the species of the same genus are exceedingly common mold-like saprophytes forming black, moldy growths on dead sticks, stems, seeds, etc. The plum scab is found on plums and cherries. Spots arise on the fruits shortly before ripening. These spots are covered with brown or olive growths of fungus threads from which dark spores are pinched off. The spots may increase in size and number until the whole fruit is covered. The latter then shrivels and is rendered unfit for the market. Many varieties of plums are attacked and the wild American plum seems to suffer as much if not more than any other variety. The fungus is probably one of the black fun- gus group of the sac fungi but its winter-spore stage has not yet been discovered. It is possible that the fungus lives over the winter in a sterile thread condition on the branches and bark of trees. The fungus has been observed in Minnesota but the ex- tent of its damage is not yet known. Spraying with bordeaux has been recommended. Several treatments should be given, beginning when the flowers are well set. Diseased plums should be destroyed. Black rot of apple (Sphaeropsis malorum Peck.). The black rot attacks apples usually in the ripening stages or when the fruit is in storage. It also attacks the leaves, forming reddish brown spots, or the twigs, where blackish spots are produced. The 364 Minnesota Plant Diseases. FIG. 194.— Black rot of apple. After Clinton. fruit, when attacked, turns at first a reddish brown but later be- comes black. On attacked portions of the tree the fungus pro- duces its spores. It is an "imperfect" fungus and produces spores in. small capsules, which appear on the leaf, twig or fruit spots as tiny black warts. These open to the exterior by minute pores through which the spores, which are cut off of threads lin- ing the interior of the capsule are thrown out. The treatment which is I used against the apple scab is lusually recommended in treat- ing black rot. In addition, th^ dead twigs and limbs should be pruned to prevent the win- tering of the fungus in the twig- spots. Rotted fruit should be removed and destroyed. Win- ter spraying has also been recommended. Apple and pear blight [Bacillus ainylovorus (Burr.} DeToniJ]. This disease is also known as fire blight. Its cause is a bacte- rium. The bacteria gain entrance to the twigs of the apple through wounds or through the flowers. They are carried by insects to the stigma of the flo\ver and from this point work their way into the branches. On the branches they form first small, dead spots, which later enlarge to canker- like sores, from which a dark mucil- aginous fluid oozes. In this fluid one finds millions of bacteria. In the canker growth b'utyric acid, carbonic acid gas, and alcohol are formed. The branch above the canker is killed, often suddenly, and the leaves turn brown as though scorched by fire, hence the common name of fire blight. No successful remedy for diseased branches is known. Pruning back is the only successful method of combating the disease. FIG. 195. — Fire blight of apples. Bacteria which cause the dis- ease. Highly magnified. Aft- er I>. M. Duggar. Minnesota Plant Diseases. igr O 0 The branch should be cut six inches below the canker and care should be taken to keep the knife clean, since it is an eas> matter to transfer the bacteria on the knife Wade to hea1thy trees. The blade should therefore be dipped in a corrosive sub- limate solution. All diseased twigs should be promptly burned. Since an abundance of moisture in the plant favors the develop- ment of the bacteria, an avoidance of a too succulent condition has been recommended, e. g., draining the moisture from around the base of the tree. This procedure has aided in keeping the disease in check. Downy mildew of seedlings (Phytophthora omnivora DeBy.}. See Diseases of Greenhouse and Ornamental Plants. Vineyards. Black rot of the vine [GitignanHa biJwcllii (Ell.} Viala et Ra-rJ]. This fungus has often proved a very destructive disease and vine growers in the United States have suffered great losses from it. The extent of damage in Minnesota is as yet unknown, though the fungus is probably not uncommon. It has caused considerable trouble in Iowa. The first indication is the produc- tion of small reddish or brownish spots on the leaves. On these spots arise minute, black, capsular fruiting-bodies. These cap- sules do not contain sac-spores, but produce one kind of summer- spore. These spores are formed on threads in the capsule and escape in a sticky mass from the apical opening. They are washed apart by the rain and distributed to other parts of the plant. The berries are also attacked and brownish spots appear on them. Capsular summer spores are formed here similar to those on the leaves and in addition to these two other spore-forms may appear. The berry shrivels and dries up and becomes black, but still clings to the vine. Late in the fall the sac-spore cap- sules appear on the shriveled grapes. They are small black bodies with an opening, through which the sac spores escape in the following spring. These sac spores probably recommence the infection. All diseased portions should be promptly removed and burned. All infected grapes should be destroyed and in no case should the shriveled grapes be left on the vine until spring. The disease needs prompt and persistent attention and a fight of 366 Minnesota Plant Diseases. several years is necessary to hold it down to a minimum o-f dam- age. Spraying with bordeaux has been found very beneficial. Spraying should commence early and continue at intervals of about two weeks until a few weeks before the ripening of the fruit. In these later sprayings, ammoniacal copper carbonate should be substituted for the bordeaux. Powdery mildew of vines [Uncinula necator (Schw.) Burr.]. This is one of the most destructive of the powdery mildews or blights. It attacks grape vines and causes much damage, not only to the leaves but also directly to the fruit. The summer spores are formed in the usual manner for powdery mildews and appear in great numbers spreading the disease very rapidly. The spread is particularly rapid in moist weather. The mycelium first appears in whitish areas, under which the cells of the leaf are killed, leaving brown spots. The leaves usually wither. The grapes dry up in the attacked region and often become split open and subsequently wither or decay. The summer spores are formed throughout the summer; and in the fall the sac spore capsules appear as dark-brown bodies of minute size. The cap- sule is provided with a crown O'f numerous thread-like append- ages, the tip of each of which is bent back in the form of a stout terminal hook. When broken open each capsule is found to con- tain four to ten sacs, each of which contains four to eight spores. The disease winters over in the capsular stage and infection is accomplished in the spring from the sac spores, which alight on the leaves. Here they send out a small tube with a flattened disc, which serves to attach the parasitic plant to the leaf. A short sucker branch is then sent out into a cell of the host and the growth of the mycelium proceeds. From this mycelium the summer spores arise. "Treat as for downy mildew with perhaps a late spraying in the fall after gathering the berries, to destroy the winter spores. Potassium sulphide is also used effectively against this fungus/' (Conn. Ag. Ex. Sta. Bull. No. 142 — 1903.) 'The sprayings with bordeaux mixture, that are generally applied for other diseases, will do much to hold it in check, during the early part of the season ; but later on, as the fruit approaches maturity, the weak copper sulphate or the ammoniacal carbonate of copper will be preferable. The application of flowers of sul- Minnesota Plant Diseases. 367 phur to such varieties as are subject to this disease, at intervals during the season, will also be of value, especially on grapes grown under glass. In dry seasons the frequent stirring of the soil will aid in keeping the vines healthy, but upon the first ap- pearance recourse should be had to one of the above fungicides.1' (Mich. Ex. Sta. Bull. No. 121.) The burning of the fallen leaves of infected plants is also to be recommended. Anthracnose of vines (Sphciceloma ampelinum DeBary). This is also known as birds'-eye rot. The cause of the disease is an imperfect fungus and causes great damage in many states of the Union. The extent of its work in Minnesota is not yet known. All parts of the plant are attacked and the disease is a difficult one to combat. The fungus causes small black spots, which later become whitish, though the edge is margined with purple. The spots in the stem sink, leaving depressed regions, while in the leaves dark-brown spots are produced, from which the tissue sometimes falls as in the shot-hole fungus of plums. On the fruit circular spots are produced with a black margin, outside of a red ring, from which the fungus derives its name of birds'-eye rot. The spots may be numerous on a berry and eventually become scabby. An infected cluster of berries bears usually few or no sound ones. The berries die and shrivel but remain attached to the vine. The spores of the fungus are borne in small, black spots, which appear on the leaf and fruit spots. The spore-bearing threads are packed into a cushion which is dark-colored. From the surface of this cushion arise the upright thread branches, bearing colorless spores. The treatment for black rot of grape is usually recommended for the anthracnose. All diseased portions should be removed. In addition to this, a winter treatment is given in Europe, where the disease was first known and where it has caused a great dam- age. In the old world this disease has been brought under con- trol by winter and summer spraying and the destruction of in- fected parts. "In Europe it is the custom to wash the vines and stakes during winter or early spring with sulphuric acid and sul- phate of iron solution. The liquid is applied by means of swabs or brushes. It blackens the canes and this is a test of the thor- oughness of the work." (See chapter on fungicides. Iron sul- phate solution.) 36S Minnesota Plant Diseases. "If after two or three clays there remain portions which are unchanged in color the vineyard is treated a second time, partic- ular attention being paid to the parts omitted at the first treat- ment." Lodeman (The Spraying of Plants, p. 295.) Downy mildew of vines [Plasmopara viticola (B. & C.) Bcrl}. This is a very destructive disease of vines originating in the United States, but since about 1878 causing enormous destruc- FiG. 196.— Downy mildew of grape. Under surface of a leaf, showing down of mildew threads spread over the entire leaf. Original. tion of vines in Europe. The fungus is a downy mildew and is a destructive parasite. It appears on all above-ground parts of the vines, but most abundantly on the leaves. When the latter are attacked they show, from above, pale green spots which later become light yellow in color. This is the region where the my- Minnesota Plant Diseases. 369 celium is at work within the leaf. On the under surface these patches show at first a faint light grey shimmer, which later de- velops into the grey mold-like growth of the fully developed patches of the summer spores. These patches spread rapidly and the whole leaf, in the course of a few weeks, dies, becomes brittle and useless as a starch-making organ and dangerous as a pro- FiG. 197. — Downy mildew of grape. On the right is a healthy bunch of grapes; on the left a bunch badly diseased. Original. ducer of the fungus spores. The so-called spores behave as do those of the downy mildews generally, i. e., when they fall in very moist surroundings they produce six or more swimming spo-res, which swim about in the water drops and spread the infection on the leaf. When they come to rest they germinate by sending out infection tubes and the latter establish new regions of the myce- lium. The leaf patches commence to appear in early summer. Minnesota Plant Diseases. Later in the year the winter spores are formed in the usual way for the downy mildews, i. e., from breeding organs. The winter spore has a thick coat and remains in the leaf after the latter falls. In the spring the decay of the leaf sets the spore free, and in moist conditions it produces numerous swimming spores ; the infection of the vines follows in the usual way. The destruction of fallen leaves, to avoid future infection, is therefore seen to be of im- portance. FIG. 198. Downy mildew of grape. A. Section of a leaf with spore-bearing threads emerg- ing from an air-pore. B. Greatly enlarged sucker threads, h. C. Formation of swarm soores in the so-called summer spores; 1, summer spore (is really a spore-case) ; 2, same with protoplasm divided into regular areas; 3, areas of 2 are seen separated, and the whole mass escaping from the spore-case; 4, an escaped and free area of the protoplasm which becomes the swarm spore, 5. D. Formation of egg-spores by the breeding act. Highly magnified. After Millardet. The treatment for black rot is usually recommended for this disease. The sprayings may be at longer intervals. (See Black Rot of Grapes.) Disease-resisting varieties may also be used. It has been rec- ommended that the vine be treated in the fall or early spring, be- fore the buds commence to open, with an iron sulphate solution. Chapter XXL Diseases of Greenhouse and Ornamental Plants. Jff Carnation smut [Ustilago violacea (P.) Fckl.]. This smut at- tacks a large number of species of the plants belonging to the pink family, such as common garden-pinks and carnations, and such wild flowers as catch-flies, star-worts, soap-worts and corn cockles. This is a very different disease from the rust of carna- tions and cannot easily be confused with it. The carnation smut attacks the stamens of the flower and converts the anthers into smut-spore sacs. The smut spores form a violet-colored powder and one can easily mistake this for abnormally colored pollen. When the smut spores escape, many fall upon the petals and sepals discoloring them and rendering them unfit for decorative use. This fungus often exerts a remarkable influence upon those members of the pink family which have pistillate and staminate flowers, e. g., the corn cockles. The pistillate flowers, when at- tacked, develop stamens which, in an unaffected flower, remain undeveloped. These stamens, as well as those of the presence of the fungus, and the latter can only be detected at the ripening of the spores, or by a previous examination of the anthers. The diseased plants should be promptly destroyed to prevent a spread of the disease. The violet smut [Urocystis violae (Sozv.) Fisch.]. Occasion- ally on pansies and violets. (See Diseases of Wild Plants.) The chrysanthemum rust (Puccinia chrysanthemi Rose.). This disease has appeared in recent years as an abundant parasite on greenhouse chrysanthemums. It is not, as was formerly sup- posed, identical with the common wild rust of sunflowers and their allies but it is a distinct importation, probably, from Japan. The summer spores are found in the fall and are produced in 372 Minnesota Plant Diseases. very small clusters, which arise in great numbers, chiefly on the under surface, but also on the upper surface of the leaf. These sometimes coalesce to form larger spots. The clusters are at first closed by the epidermis of the leaf but later break out and expose a dark-brown powder of summer spores. The winter spores are two-celled and are produced in black clusters. They are not, however, common in this country. On account of this latter feature the disease should not be very difficult to combat. It is said to tend to disappear of itself after a regular run of a given greenhouse. Great care should be exercised in preventing the introduction of the disease into a greenhouse. This can be done by close examination of all purchased cuttings and plants and by carefully watching them for some time after their intro- duction. The diseased plant parts should be promptly removed and burned. In case of a persistent attack, "every leaf and stem above ground should be destroyed at the end of the flowering period and the young plants or cuttings, for the next season's supply, be grown in an uncontaminated house, and, if possible, fromuncontaminated material." (Ind. Ex. Sta. Bull. 85 — 1900.) It has been reported that inside cultivation in summer and selection of rust-free stock will be sufficient to keep the disease in check. Rust of hollyhocks and mallows (Puccinia mdvaccarum Mont.). The mallow rust attacks members of the mallow fam- ily, e. g., hollyhocks, marsh-mallows and the small, wild, creeping mallow. It produces only winter-spores which can germinate without a resting period. The spore groups occur in great abundance on the leaf-stalks and leaf-blades and even on the floral parts, causing deformation of these parts. In some cases the plants are killed by the parasite. The mallow rust has an interesting history. It was intro- duced from South America into Europe by the Spanish about thirty-two years ago. Before this time it was unknown in Eu- rope or North America. It spread in Europe with remarkable rapidity, growing on cultivated and wild mallows, and is at pres- ent an exceedingly abundant and dangerous enemy to mallow growers. It is said to have completely exterminated mallows in many regions. This disease has been introduced from Europe into the United States and is fast gaining ground. It has not yet been reported from Minnesota but will probably reach this state in due time, if not already here. Minnesota Plant Diseases. Spraying with bordeaux mixture or a solution of permangan- ate of potash has been recommended. Diseased parts should be immediately destroyed. The violet rust [Pnccinia violcc (Schnm.) DC.}. On all spe- cies of our native violet can be found, often in considerable abund- ance, this rust of violets. It also occurs on the cultivated violets of greenhouses and may cause considerable damage. Cluster- cups are formed on our wild violets, often in great abundance, in the spring. Slight swellings of the leaf and distortion of af- fected parts are usually caused, and the cluster cups occur on the surface of the malformations. Later, summer and winter-spores are formed, in small round patches, also, usually on the under surface of the leaves. These do not usually show malformations as in the case of the cluster cups. Infected plants or plant parts should be destroyed. The carnation rust [Uromyces caryophyllinns (Schrk.) Schroct.]. On the leaves or stems of the carnation often appear elongated, brownish patches, breaking through the epidermis and exposing a more or less powrdery mass of spores underneath. These proceed from the mycelium, which lives in the stem and leaves. The first spores produced are the summer spores and these are light brown in color. They germinate immediately after formation, and aid in spreading the disease. Later in the season, darker, winter-spores are produced and these pass the winter before germinating. The mycelium, when once estab- lished in a plant, remains there and forms pustules of spores in succession. Diseased plants should not, therefore, be used for cuttings, since the latter are sure to be infected. This disease has proved very serious at times to carnation culture. Diseased plant parts should be cut out and destroyed to pre- vent the spread. Bordeaux in fine spray at intervals of one to three weeks has proven effective in checking the disease. Potas- sium sulphidf has also been recommended. The cultivation of hardy varieties has been suggested and particular attention should be paid to proper methods of cultivation, ventilation and watering. The sunflower rust (Pnccinia tanaccti DC.). This is one of our most common rusts, occurring in great abundance on almost, if not all, species of Helianthus and is particular^ abundant up- on the common cultivated Helianthus annuus. In addition, it 374 Minnesota Plant DiseaseSe occurs on other more or less closely related plants. The fungus mycelium gains entrance to the plant in the spring and first pro- duces cluster cups. These are followed by the summer spores, throughout the summer months, forming small red-brown patches FIG. 199.— Leaf rust of roses. The cluster-cup stage on the stems and leaves. On left is a stem distorted by the cluster-cup cushions. Photograph by H. Cuzner upon large, dark, red:brown spots in great abundance, on the lower surface of the leaves. The summer-spores are followed toward autumn by the winter-spores, which are formed in similar but darker groups. The winter-spores are two-celled. Where Minnesota Plant Diseases. „,- 375 the sunflower has been raised in large quanti- ties, this rust has often proved very injurious. The leaves and all parts affected by the fungus should be burned in autumn to destroy the winter spores and to prevent the recurrence of the disease in the following spring. (See Fig. 206.) The rose leaf rust [Phragmidium subcor- ticium (Schrk.) Wint.}. This is a very com- mon disease of both cultivated and wild roses. All three important spore-forms are formed upon the same host plant. The cluster-cup stage appears in early summer, or late spring, and causes a distortion of the attacked parts. These are usually swollen and badly bent and become bright orange in color. The summer spores appear later and are also brightly col- ored. The winter spores appear last and are formed in small, round, blackish patches on the under surface of the leaf. These spores form a fine, small, powdery mass. The spores are long and are divided into a number of cells, often about seven or eight, arranged in one row, and have a long club-shaped stalk. Care should first be taken to prevent the wintering over of the disease. This can be clone by destroying the old leaves, particularly those of diseased plants. Late fall or early spring treatment with a strong copper sulphate solution will also aid in destroying the winter spores. The dormant bushes and the ground near them should be drenched. The spread of the cluster-cup and summer-spores can be Fl0Gf rosei. stem wStfa prevented by spraying after the buds open with groups of cluster- • 1 i cups. Original. bordeaux or ammoniacal copper carbonate. The rose stem rust (Phragmidium speciosum Fr.) This rust is a near relative of the leaf rust of roses but is not identical with it. The attacked stem of the rose becomes swollen and distort- ed, and soon a large winter spore pustule is formed which looks 376 Minnesota Plant Diseases. not unlike a smut mass. The spore mass is black and powdery and the spores are, in general features, similar in appearance to the winter spores of the leaf rust. Infected plant parts should be destroyed before the spores have a chance to disperse. The Indian turnip leaf rust [Uromyccs caladii (Scliw.) Far!.]. This rust is sometimes found on cultivated Aroicls. (See Dis- eases of Wild Plants.) Golden-rod and aster leaf rust [Colcosporium sonchi-ar- vcnsis ( Pers.) Lev.]. The golden-rod rust is an exceed- ingly abundant disease upon almost if not all of the spe- cies of golden-rod, asters and their allies, found in the state. The bright orange-red summer spores appear in great numbers chiefly on the under surface of the leaves, and form a bright- colored powder. Often the en- tire lower surface of the leaf will be covered with the spore groups. The winter spores arise later in light-colored, crust-like groups. These spores remain attached to the leaf throughout the winter and germinate in the following FIG. 201.— Leaf rust of roses. r-pt T branch and leaves infected wi spring. They do not germi- nate in exactly the usual way for rust winter-spores for they do not send out a thread in the ordinary manner. Four spores are, however, produced from each winter spore and each is borne on a stalk which comes directly from the spore which has been previously divided up into four cells by cross walls. The cluster- cup spores are probably formed on some coniferous trees. Cultivated plants may be treated with ammoniacal copper car- bonate, early in spring, and the treatment should be continued every two to four weeks. (Fig. 205.) 1. Rose cluster- cup stages of the disease. 2. Leaf with clusters of winter spores. 3. Win- ter spores. 4. Summer spores. 3 and 4 highly magnified. After Massee. Minnesota Plant Diseases. 377 Cedar apples of red cedar (Gyinnosporanginin macropus Linkr and G. globosnm Fan.). See Leaf Rust of Apples. Diseases of Orchards and Vineyards. The powdery mildew of lilac [Microsphccra alni (Wallr.) //'/"///.]. This is the very common blight of lilacs which, in the fall, covers lilac leaves with a conspicuous white mycelial coating. The same blight is apparently found on many other plants, as alder, birches, high bush cranberry and others. Summer spores are produced in the usual manner for powdery mildews and the FIG. 202. — Powdery mildew of lilac, showing the white patches of the fungus mycelium. Original. sac capsules appear in the fall. The latter are furnished with appendages similar in shape to those of the apple powdery mil- dew. Unlike this blight, however, the sac-capsule of the lilac mildew contains more than one sac. The presence of the blight on the lilac, though it undoubtedly draws some nourishment from its host, does not seem to exert any serious influence upon it. Burning of the fallen leaves in the autumn has been recom- mended. Spraying is usually not practiced since the disease or- dinarily does no serious injury. Ammoniacal copper carbonate or potassium sulphide would probably prove effective against it. 378 Minnesota Plant Diseases. The powdery mildew or blight of the rose [Sphaerotheca pannosa (Wallr.) Lev.']. An enormous amount of damage is sus- tained yearly by the ravages of this blight in gardens and green- houses. The leaves of the attacked rose bushes become covered with a fine white coat of the fungus mycelium and often become distorted or stunted in various ways. The young leaves and buds are especially damaged, and many leaves are killed. The mycelium sends suck- er-like branches into the interior of the epidermal cells of the host and from these draws its nourish- ment. This of course re- sults in a drain upon the host plant. During the summer erect threads are produced on the surface of the leaves and these ( form chains of spores, which are carried about by the wind and rapidly spread the disease from leaf to leaf and from plant to plant. These summer spores, therefore, act in a manner similar to those of the ,wheat rust. Toward late summer and fall small black bodies about the size of a pin-point are formed on the mycelium, and these are the closed sac-capsules. They are yellowish-white, when im- mature, becoming black when mature; they are attached to the mycelium by special brownish appendages. They have a more or less membranous wall, which is divided into polygonal areas. The sac-capsule, when broken, shows a single, spherical, colorless sac, in which are found eight oval spores. The sac-capsule does not open until spring, when the wall decays, setting the spores free. These spores, therefore, function as winter spores. In the spring they germinate, by sending out a fine tube, which again FIG. 203.— Powdery mildew of roses. A leaf of a rose attacked by the disease. After Clinton. Minnesota Plant Diseases. 379 infects a rose plant. The mycelium, thus produced, soon com- mences the formation of summer spores. It is the abundance of the latter spores, and the rapid infection by their means, that makes the rose mildew dangerous. Flowers of sulphur dusted on the leaves of the plant are chief- ly employed to prevent the germination of the summer spores. The mycelium is also killed by the sulphur treatment. "For greenhouse treatment paint hot water pipes with mixture of sul- FIG. 204. — Powdery mildew of roses, showing the superficial mycelium and summer spores on the leaves. A germinating spore is seen in the foreground. (On a peach leaf.) After Tulasne. phur and oil. Potassium sulphide or an ammoniacal solution of copper carbonate can be sprayed on the foliage. Spraying out of doors can be done with bordeaux, if there is no objection to the sediment on the leaves." (Conn. Ag. Ex. Sta. Bull. 142 — 1903.) Powdery mildew of chrysanthemums (Oidium chrysanthemi Rabh.). The powdery mildew is an occasional destroyer of chrysanthemum plants in homes and greenhouses. As in the other powdery mildews, the mycelium is superficial and forms a cobwebby or mold-like growth on the surfaces of the leaves. From this mycelium arise necklace-like strings of spores in a 380 Minnesota Plant Diseases. fashion typical for the summer spores of the powdery mildews. These spores give to the surface of the leaf a powdery appear- ance. The relationship of this summer spore to its proper win- ter-spore form has not been determined, but it is probably con- nected with the very common powdery mildew of wild com- posite flowrers (Erysiphe cichoracearum) or some closely related species. It has never been reported as appearing in dangerously large numbers in any greenhouse in this state. It would proba- bly yield to the common treatments for powdery mildews and other superficial parasites, e. g., ammoniacal copper carbonate or potassium sulphide sprays. The drop of lettuce (Sclerotinia libertiana FckL). This fun- gus has been found very destructive in eastern greenhouses. It attacks many kinds of lettuce and has been found to be the chief enemy of lettuce culture under glass. The fungus is also remark- able in that it is identical with the cause of a rotting-disease of cucumbers. The drop fungus is a cup fungus. The mycelium is parasitic on the lettuce leaves and stem and attacks the plant very vigorously, producing complete collapse and quick rotting. As the rotting of the leaves proceeds, the fungus threads com- mence to form small storage organs, usually on the lower sides of the fallen leaves. These storage organs or sclerotia are about the size of a large pin head, or slightly larger, and are composed of densely woven masses of fungus threads, stuffed with nutrient material. There are sometimes produced considerably larger sclerotia, and these give rise to the cup form of fruiting body, which bears the sacs on the upper surface. Usually, however, the small sclerotia only are produced in greenhouses and these do not produce the cups. They are, however, very resistant bodies and will survive very unfavorable conditions for a considerable length of time. Thus they carry the disease from one crop to another. Freezing or drying, instead of killing them, accelerates their development when conditions are again favorable. In the latter case the sclerotium fungus threads resume growth and a fine mold-like mass of threads issues from it. These threads are vigorous and can immediately infect the lettuce plants. The fun- gus thrives best under conditions most favorable to the growth of the lettuce and the greatest amount of damage is done when the lettuce is about mature. Ordinary methods of prevention, Minnesota Plant Diseases. ^81 such as spraying, are not available for reasons that poisonous substances cannot be used on the lettuce and also that the ordi- nary sprays do not affect the sclerotia. The most effective rem- edy is a complete or at least partial sterilization of the soil. A coating of five-eighths or three-fourths inches of sterilized sand or earth will materially reduce the effect of drop, while four inches has in certain experiments completely destroyed all of the disease. The drop can also be greatly reduced by treating the soil with hot water which will raise the temperature of the sur- face to 176° F. to 1 86° F. Lime, sulphur and charcoal applica- tions and coatings of saw-dust and coal ashes have been found to be ineffective against drop. Good ventilation and good drainage will help to keep it in check. The grey mold of lettuce (Botrytis vnlgaris Fr.\ This fun- gus appears on greenhouse lettuce, causing a leaf rot. The fun- gus has been described as a saprophyte and it is claimed by recent investigators that it is net at all parasitic. The supposition that it is the summer stage of Sclerotinia libertiana has also been denied. The grey mold of lettuce appears as a fine greyish mold on the rotting leaves. When dry the moldy growth, if shaken, throws off a fine dust of spores which may rapidly spread the disease. The grey mold is probably not responsible for so much damage as is the drop fungus (Sclerotinia libertiana) with which it has been confused. It can be controlled by the same treatment as the drop fungus. Leaf spots of violets (Phyllosticta violae Desni. and Cerco- spora violae SaccJ). This is a very common and destructive dis- ease of greenhouse violets. There are two kinds of fungi pro- ducing two kinds of spots, which are, however, not very easily distinguished from each other. The Cercospora spot is, in gen- eral, a cleaner cut spot, while the Phyllo-sticta may be more dif- fused. Both are whitish and have dark centers where the spores are formed, in the former case, in a loose weft, in the latter, in dark spherical receptacles or capsules of very minute size. The two diseases may be intimately associated. When the spots are numerous, the leaf may be killed off, and the entire plant some- times dies. The fungi are both plants of the Imperfect Fungi. Bordeaux has been found useful in combating the leaf spots, though it does not entirely prevent them. A quarter strength 382 Minnesota Plant Diseases. has been recommended for plants under glass — the weak solution will obviate the injurious effects of stronger solutions in retard- ing flowering. Plants in the open field should be sprayed throughout the summer with one-half strength bordeaux every ten days. The downy mildew of seedlings (Phytophthora omnivora DeBy.\ This fungus pest is a parasite on seedling trees of many families of plants. It is especially destructive in nurseries where it may destroy seedlings of conifers and many other plants. It is not dangerous to older plants but confines its attack to young seedlings which have produced only a few leaves. It appears first on the stem, cotyledons, or first leaves, as brown or blackish patches. On these patches develops a very delicate film of spores produced in a manner very similar to those of downy mildew of potato. These spores may germinate directly to an infection tube or they may produce swimming spores, just as do the spores of the potato mildew. The parasite shows little choice of host except in the selection of young plants. It is therefore amateur- ish in its style of parasitism, but it is nevertheless very de- structive. In a few days' time it may destroy whole beds of seedlings. It produces winter spores by a breeding act, as is common among the downy mildews. When the pest appears in nurseries, if only on a few plants, these can be destroyed. The most effective methods are, how- ever, those of ventilation and drainage. The fungus thrives best in very moist situations and in moisture-laden atmospheres and in shaded positions. By avoiding as far as possible these condi- tions the fungus may be kept in check. As the winter spores are very resistant, diseased plants should be carefully removed and destroyed and plots which have been infected with the disease should not be used for the same purpose for several years. The damping-off of seedlings (Pythium debaryanum Hesse.}. Seedlings of plants of the mustard family are particularly liable to become infected with this disease. Many other paints, how- ever, as clovers, corn and a great variety of others, have also been known to suffer from it. Potato plants and potato tubers in storage may be attacked, if the moisture is excessive. The dis- ease usually appears where seedlings are too densely crowded to- gether, or in shady places and where there is excessive moisture. Minnesota Plant Diseases. 383 The evidence of the presence of the disease is seen in the falling over of the seedlings and their subsequent death and decay. The fungus requires a great deal of moisture and attacks the stem of the seedling at the surface of the ground. It is very destructive in its attack and kills off the tissues at this point, causing the fall of the seedling. The spores are formed only in the presence of moisture and the plant is able to live in a saprophytic manner. It is a primitive, but directly destructive, parasite. Under favor- able conditions the fungus will spread very rapidly and cause great destruction to beds of seedlings. The summer spores are of two kinds. One germinates usually very soon after forma- tion, producing directly an infection tube. The other is some- what like the so-called summer spores of downy mildew, but un- dergoes a resting period, after which it breaks up into' swimming spores. Each of the latter is provided with two lash-like pn>- cesses, which aid in its swimming about in the water. When these swimming spores come to rest they germinate into* an in- fection tube which attacks new seedlings or builds up an aquatic mycelium. The winter spore is formed by a breeding act and is provided with a very thick wall so that it can undergo long periods of rest. When it develops further it produces swimming spores, just as do some of the summer spores. Plenty of sunshine and good drainage will keep the fungus in check. Soil which contains many winter spores, or resting summer spores, should be avoided. (Fig. 34.) The damping-off of prothallia(PW/m^n intermedium DeBy.}. This fungus is a very close relative of the damping-off of seed- lings and its behavior is somewhat similar. The host plant is, however, the sexual plant of the ferns, commonly known as the prothallium. The fungus is a common enemy of fern culture in greenhouses, when ferns are raised from spores. The fungus permeates the tissues o*f the prothallium and the latter wilts, be- comes dark in color, dies and decays. The fungus produces sum- mer spores in a manner, in general, similar to that of the damp- ing-off of seedlings. The so-called spores form, under proper conditions of moisture, numerous swimming spores, and these behave in a peculiar manner ; for, when they cease to swim, they move in an amoeboid manner until they finally come to rest and germinate. 384 Minnesota Plant Diseases. "If the pots or vessels in which the prothallia are grown are rested on sphagnum, a layer of which can be placed in the bottom of the Warclian case, and after the young prothallia have started, all of the watering be applied through this, the prothallia will clo much better than if surface watering is practiced, and far better than \vhere the pots are rested in a vessel partly full of water. The air of the Wardian case or of the house should not be kept too clamp." (Cornell Ag. Ex. Sta. Bull. 94 — 1895.) The downy mildew of violet (Peronospora viola; DeBy.). This disease is well known in Europe, where it attacks cultivated violets and pansies, both in greenhouses and in gardens. It is also known in the United States, though it has not been reported from Minnesota. The summer spores are borne on threads, which come out of the leaf on its lower surface and form there greyish, downy masses of mildew. They are produced on threads in a manner similar to those in the downy mildew of mustards. Good ventilation and abundant sunlight and the avoidance of damp conditions will keep the fungus in check. It thrives only in moist conditions. Mildew of mushroom (Sporodinia grand is Link.). (See Dis- eases of Wild Plants.) Chapter XXII. Diseases of Wild Plants. Jff Gall disease of the blueberry, cranberry and other heaths [Exobasidium vaccinii (Fckl.) IVor.]. Plants of the heath fam- ily, e. g., cowberries, blueberries and true cranberries, may be at- tacked by a fungus which produces malformations of branches and leaves. Flowers and flower-stalks are also attacked in some cases, and the formation of fruits prevented. Sometimes the leaf swells up into enormous kidney-shaped, fleshy bodies which are many times thicker than the normal leaves. The hypertrophied portions, where exposed to the light, are colored red. A cut through such a leaf shows it to be composed of a fleshy mass, through which the branching veins can be clearly seen. These veins are much reduced in structure from the normal and contain but a small amount of woody material. The fleshy portions have almost completely lost the power of starch-making, as is shown by the small amount of leaf-green present and by the entire ab- sence of large air-spaces. The fungus threads are very fine and are found only in the attacked regions. They run between the cells of the host, and at the surface of the leaf form a rather dense weft, just underneath the cuticle of the external layer of cells. From this weft numerous spores are produced on basidia, which are arranged in a palisade. The spores can be seen with the naked eye as a fine, white powder on the surface of the leaf. Under the microscope the spores are seen to be produced on small, finely-pointed stalks, four arising from a single cell. When these spores fall on the young leaves or stems of the host-plant they germinate into fine germ-tubes, which penetrate into the leaf through an air pore, or directly through the walls of the outer row of cells, and from this point spread into the mature mycelium. The presence of the mycelium immediately stimulates the leaves to the above-described abnormal growth, which takes place at the expense of the neighboring parts. All diseased plant parts should be burned. (See Fig. 37.) 25 386 Minnesota Plant Diseases. Rust of Pyrola [Chrysomyxa pirolae (DC.) Rostr.]. On all species of Pyrola found in the northern part of the state occurs a Pyrola rust. It is found chiefly in the spring and often occurs in great abundance. The cluster-cup stage is not yet known, but is probably to be found upon some needle-leaved evergreen tree. The summer spores are by far the most abundant and appear in early summer. Their spore groups often completely cover the lower surface of the leaves with a golden-orange powder-mass. The winter spores form darker, crust-like masses, which are much less abundant. See Leaf Rust of Pines, Chapter XVI. The rust of milkweeds [Cronartium asclepiadeum (Willd.) Fr.]. This rust is very well known in Europe as a parasite upon many species of the milkweed family. It seems to be very rare, or entirely wanting, on milkweeds in this state, but what is prob- ably the same rust has been found upon the leaves of the oak, not, however, in great abundance. The winter spores, preceded by the summer spores, are formed on the above-named hosts, and the cluster-cups probably on the pines. It is the disease which is produced upon pines that is of chief importance. See Leaf Rust of Pines, Chapter XVI. Cluster-cup rust of various wildflowers (Species of Aecid- iuni). Many of our spring wild flowers, such as buttercups, may- flowers, columbines, squirrel- corn, Dutchman's breeches, Old Man's beard, white cohosh, Solomon's seal, false Solomon's seal, lilies, evening primrose, elder, violet, etc., are attacked by the cluster-cup stages of rusts. In comparatively few cases is the connection between these and the winter-spore stages known. These cluster-cups are found, often in great abundance, from early spring until midsummer and are usually found on yellowish spots, on the under surface of the leaf. On the upper surface of the same spots are formed the little accessory spore-capsules known as pycnidia. These are flask- or pear-shaped bodies, opening in small yellow or black dots, onto the upper surface of the leaf. They often exude a sugary solution. Their behavior is problematical but they are probably vestiges of former func- tional male, reproductive cells. A few of these cluster-cup diseases, such as the cluster-cup rust of gooseberries and currants, have been considered in detail Most of them are of minor importance economically, so that pre- ventive means need not be considered. Minnesota Plant Diseases. 387 Cluster-cup of gooseberry and currant (Aecidium grossu- laricu Schitm.}. This is very common on wild gooseberries and currants. See Diseases of Garden Crops. See also Rust of Sedges (this chapter). Cluster-cup rust of composites (Species of Aecidium). A number of cluster-cup rusts attack wild and cultivated plants be- longing to the composite family, e. g., sunflowers, asters and goldenrods. Very little is known of their relationships with the other spore-forms. They occur in abundance, throughout early summer and midsummer, and are usually found on yellow spots, accompanied by the pycnidia or accessory spore capsules, as in the rusts of wild spring flowers. These cluster-cup rusts must be distinguished from the golden-rod rust, which is caused by a dif- ferent fungus and is even a different spore-form. A close ex- amination, even with the aid of a hand lens, will serve to dis- tinguish between them. The cluster cups are very easily recog- nized. Leaf rust of golden rod and aster. See Diseases of Green- house and Ornamental Plants. Rust of sunflowers (Piiccinia tanaceti DC.). See Diseases of Greenhouse and Ornamental Plants. Rusts of ferns [Hyalopsora polypodii (P.) Magn.]. Our common wild ferns are subject to a rust disease, which is not un- common in this state. The fragile fern is frequently attacked. Summer spores are produced on the under surface of the leaves. The winter spores are scattered through the fern tissues. They are not as conspicuous as the summer spores. The latter occur in dark, rust-like patches, often covering considerable areas. Stem and leaf rust of cowberry (Calyptospora goeppertiana Kilhn\ An interesting disease of plants of the blueberry family, similar in some of its effects to* those of the fungus leaf gall of the same plants, is caused by a rust fungus. This attacks chiefly the cowberry and other related species. The young shoots are attacked and the affected branches become much larger than the healthy and are swollen to several times their normal thickness. This swelling takes place the year following the infection of the plant. The parasite lives in the tissues for several years and the formation of fruits is usually pre- vented on such affected shoots and the latter are finally killed. Minnesota Plant Diseases. FIG. 205.— Golden-rod rust. Shows black spots, which are clusters of winter spores occurring in crust-like cakes. Original. Minnesota Plant Diseases. 389 The fungus threads, which are found in the swollen parts of the host plant and which cause the stimulation, whereby the increase of growth or swelling of the stem takes place, form their winter rust-spores inside of the cells of the epidermis of FIG. 206. — Sunflower rust. Winter and summer spore clusters on the leaf of a sunflower. Original. the host. This epidermis is much altered on account of the action of the fungus. Its cells have thin, instead of thick, outer walls, and are much increased in size. These spores germinate in the spring in the usual way, except that they 390 Minnesota Plant Diseases. remain in the cells of the host. The cluster-cups are found on the leaves of some coniferous tree. Spruces in the neighbor- hood of affected cow- berry plants often show an abundance of cluster cups and are usually most seriously attacked in the lower branches. It has not been proven in our American plants that these two stages are con- nected, but there seems to be considerable proba- bility that such is the case. Rust of a n emone (Puccinia fusca Relh.}. Anemone, Thalictrum and allied genera are sub- ject to the attack of anemone rust. In this rust only the winter spores are produced. The af- fected plants are consid- e r a b 1 V deformed. The leaf Stalks are longer and the leaf blades are thirk ened The SOOre 9TOUOS are found on the lower surface of the leaves. The winter spores of the anemone rust pass the winter in a resting condition on the dead leaves of the host and germinate in the spring. Rust of wild sarsaparilla (Triphragmium clavellosum Berk.}. Although found only rarely in some places, this rust is very com- mon in others. It is particularly abundant in the northern part of the state, but is exceedingly rare or entirely wanting in the middle and southern parts. It forms blackish, winter-spore groups on the under surface of the leaf. These groups are almost smut-like in their appearance. The spores are com- * ^^* — ^e stem rust of cowberry (a plant of the blueberry group). The fungus spores are formed in the skin cells of the host, several in each cell; they have 8erminated sending out short, divided threads, each division of which produces a short-stalked basidiospore. Highly magnified. After Hartig. Minnesota Plant Diseases. 39i posed of three cells arranged in clover-leaf fashion. The spore clusters are usually very dense and vary in size from a pin- head's width to three-quarters inch broad. The leaf under the spores colors black, so that the groups can readily be seen from the upper surface of the leaf. Cluster cups and summer spores are not known for this rust. Rust of sedges [Puccinia caricis (Sghum.) Reb.]. This is an exceedingly common rust on many Minnesota sedges. The summer and winter spores are produced on the sedge plant and the cluster-cup form is very common on the vacant lot weed, _^ ^ stinging nettle. The attacked nettle- plant parts are usually deformed and swollen, where the mycelium of the rust develops. When the stem is at- \ tacked, it is usually much bent and a \ swollen cushion arises on one side. Similar cushions arise on the leaf stalks and on the leaf blades. On these cushions which are usually orange to yellowish in color are found the clus- ter cups in great abundance. The winter-spores are found on the sedge leaves in long black rows, similar to the black rust of wheat. Not all of the rusts on sedges are of the same FIG. 208. Rust of "wild sarsaparilla; SPedeS' Though the winter shows clusters of the winter spores. may ke so similar in appearance that they can scarcely be distinguished from each other, even with the microscope, they may form their cluster cups on different host plants. The common rust of sedges, however, is that one which forms its cluster cups on the nettle. The white cluster cups of wild black currant are forms of another sedge rust. Rust of the dark green rush (Puccinia angustata Ph.). One of our commonest broad-leaved marsh rushes is frequently at- tacked by a rust, which occurs in great abundance on the leaves of the plant. The winter spores are particularly conspicuous, forming long, black lines, in which are found the densely crowd- ed winter-spores. The latter are two-celled. Minnesota Plant Diseases. Rust of Indian turnip [Uromyccs caladii (Schw.) Far/.]. This rust is very abundant in Minnesota. It is found in the wild state, chiefly on Indian turnip, but is also known on the dragon root and on other cultivated aroids. All three rust stages grow upon the same host plant. The cluster cups ap- pear in the spring and are evenly distributed over the lower sur- face of the leaf. In early summer, the summer spores are pro- duced in small, round, yellowish pustules and these are followed by the winter spores. The latter are brownish and single- celled. The mycelium is capable of wintering over in the swol- len/underground, bulbous stem, so that a plant, once infected, cannot be rid of the fungus. Infected cultivated plants must therefore be destroyed as soon as the disease appears. Cedar apple of red cedar (Gymnosporangium macropus Lk. and Gymnosporangium globosum Far/.). See Leaf-rust of Apples and Pears. Diseases of Orchards and Vineyards. Leaf rust of plums (Puccinia pruni Pers.\ On many wild cherries. See Diseases of Orchard Plants. Leaf rust of juneberry. See Birds-Nest Rust of Red Ce- dar. Diseases of Orchards and Vineyards. Club rust of juniper [Gymnosporangium clavariaefonne (Jcq.) Rees.]. See Diseases of Orchards and Vineyards. Rust of mints (Puccinia menthae Pers.}. See Diseases of Garden Plants. Rust of violets [Puccinia violae (Schum.) D. C.]. See Dis- eases of Greenhouse Plants. Rust of rose leaf [Phragmidium subcorticium (Schrk.) WintJ]. See Diseases of Greenhouses and Ornamental Plants. Smut of anemone [Urocystis anemones (P.) Schroet.]. This is not an uncommon smut upon a great number of our spring wildflowers of the crowfoot family. It is often found upon the liver-leafed anemone or hepatica. The smut forms upon the leaves, stems or petioles and produces large, black, sack-like pustules of spores. The pustule is at first covered with a thin, greyish membrane, which later breaks and releases the spores in a powder. The spores are not formed and liberated singly as in ordinary powdery smuts, but are grouped together into small spore-balls. Each ball consists of a number of spores of two kinds : there are one to several large, central spores sur- Minnesota Plant Diseases. 393 rounded by a protective coat of smaller, lighter spores, which have lost their power of germination. The spore balls escape intact as the smut powder. Carnation smut [Ustilago molacea (P.) Fckl.]. This smut is often found on wild plants of the pink family; e. g., on chick- weeds, starworts, catch-flies, soapworts and corn cockles. See Diseases of Greenhouse and Ornamental Plants. FIG. 209. — Mint rust. Winter spore clusters on the leaves. Original. Smut of violet [Urocystis violae (Sow.) Fisch.]. One oc- casionally meets with this smut on wild violets. It may occur on leaf-blades, petioles, stems or flower stalks. Definite pus- tules are formed which, when broken, disclose a black, powdery spore-mass. The flowers do not seem to be attacked and the anthers are not smutted, as in the carnation smut. The smut spores are formed in ball-like masses of cells, the outer of which 394 Minnesota Plant Diseases. form a protective coat to the inner cells, which are the func- tional spores. Diseased plants should be removed and burned. Smut of pigeon grass (Ustilago neglecta Niessl.). There are several smuts which attack the common pigeon grass. Commonly the grains are replaced by the smut-spore-mass, which is at first covered by a thin wall. These closed masses have often a purplish tinge. The spore-mass is black. Smut of bromes (Ustilago bromivoraFisch.). See Diseases of Field Crops. Root smut of sedge (Schinzia cypericola Magn.). This is an uncommon smut and would not be readily recognized as a member of the smut family. Indeed it is very possible that it does not belong to this group. It is moreover of no economic importance but is of interest on account of its root-inhabiting character, a very rare phenomenon in smuts. It attacks sedge roots forming tuber-like swellings which are often branched in finger fashion. The spores are produced internally on the ends of short threads of the mycelium. This smut occurs in Minne- sota, though very rarely. Honey dew fungi (Apiosporium, Capnodium and other re- lated genera). These fungi constitute a group of plants with peculiar habits, which have already been partially explained. They belong to the burnt-wood fungi, producing a mycelium of charcoal-like texture and fruiting bodies of the same nature. They are not true parasites, but are saprophytes, which prefer to live on the excreta of various insects. As these excreta are found largely on living leaves the fungus mycelium comes to spread over the surface of the leaf and often to completely en- close it in a dark mycelium. This position may slightly inter- fere with the light, though the leaf is seldom injured in conse- quence. These fungi do not effect any important losses to agri- cultural plants in Minnesota though a number of them are found in the state. Mold of honey-colored mushroom [Endomyces decipiens (Tul.) Reess.]. One sometimes finds upon the "mushrooms" of the honey agaric (Agaricus melleus), which is so common in Minnesota in late autumn, a mold-like parasite. The mycelium threads of the parasite permeate the tissues of the mushroom. Minnesota Plant Diseases. The spores are formed usually in fours, inside of small sacs, which are formed on the ends of branches of the mycelium. These little sacs or asci are not enclosed in any special covering but are free upon the mycelium. The red disease of mushrooms [Hypomyces lactifluorum (Schzv.) Tul.]. This is a conspicuous though not very abundant disease of wild mushrooms. It is usually found on the milk mushrooms. The disease-fungus is a member of the burnt- wood fungi, though it has not the black color of most of these plants. An attacked milk mushroom becomes greatly modified in structure. It does not form gills as under normal conditions but the entire surface of the mushroom is smooth. It is there- fore roughly top-shaped with the peg in the ground. The sur- face is colored a very brilliant red (scarlet to orange red), which makes the diseased plant a very conspicuous object in the woods. This color is imparted to it by the parasitic fungus. All over the surface one sees the slightly protruding tips of the sac-spore-capsules which are spherical to pear-shaped and are partially embedded in the tissues of the host. Through an apical opening the sac spores escape in enormous numbers so that if the diseased mushroom be placed under a bell jar for several hours, and left undisturbed, a dense white powder of sac spores from the parasite will fall on the underlying glass. These spores are presumably again capable of causing infection. Powdery mildew of hazel \Phyllactinia suffulta (Reb.) Sacc.]. Hazels are very commonly attacked by a blight, which occurs also on many other trees, such as birch, oak and ash, though not so abundantly on these. A fine, white, cobwebby mycelium is formed on the leaves, upon which the sac-capsules arise in the fall. The sac-capsules are readily recognized among the powdery mildews by the peculiar appendages which are colorless and straight, and when mature have a swollen bulb at the point of attachment to the capsule. The appendages are not very numerous. The capsules contain a number of sacs, each of which encloses eight spores. Although the disease is very common, the damage done is usually slight and does not call for combative measures. Powdery mildew of vetch and crowfoot [Erysiphe com- munis (Wall.} Fr.~\. This blight is an exceedingly common para- 396 Minnesota Plant Diseases. site on many wild plants and is also found on cultivated plants. It is found in great abundance on plants of the crowfoot and pea families. It appears on wild vetches as an extensive, fine, white mycelium, which bears the summer spores as a starchy powder, typical for the powdery mildews. The spore-sac-cap- sules are formed in the late summer and fall and appear as small black bodies about the size of a very small pin-point. The cap- sules have unbranched, brown appendages, which are inter- woven with the mycelial hyphae. They contain a number of sacs, each enclosing eight spores. This mildew, though com- mon on wild plants, is apparently not very destructive to culti- vated plants. If necessary, treatment as against powdery mildews in gen- eral would prob- ably be effective. Powdery mil- dew of compos- ites (Erysiphe cl- clwraccanun DC.). This is perhaps the most com- mon of all out powdery mildews. It is exceedingly abundant upon a great number of wild plants, be- longing chiefly to the composite family. The bo- rage and other families are less at- It is found on s u n- flowers, rag-weeds, verbenas and a host of other plants. It forms a more or less dense and conspicuous, white, cottony FIG. 210. — Powdery mildew of composites, on the leaf of the frPf|11Pntlv great ragweed. The white felt of the superficial mycelium is shown and the numerous black dots are the sac-spore- t a C K e Q. capsules. Original. Minnesota Plant Diseases. 397 coat over the leaf surface. The sac-capsules appear in the fall, but in some cases do not mature until the following spring. They have appendages somewhat similar to those of the pow- dery mildew of grasses are unbranched, dark in color and inter- woven with the mycelial threads. The capsules contain nu- merous sacs, in each of which are produced eight spores. See also Powdery Mildew of Cucumbers. Diseases of Gar- den Crops. Powdery mildew of mints (Erysiphc galeopsidis DC.). This mildew occurs on many wild plants of the mint family. The mycelium appears as a superficial whitish film on the leaves and stems. The fungus is very similar to the powdery mildew of vetches and peas. It differs from this fungus in the form of its sucker threads. The sac-capsules are formed in the fall, but do not mature until the following spring. The fungus is not known extensively on cultivated plants. In case of a serious attack the usual methods against powdery mildews would prob- ably be effective. Witches'-broom of cherry [Exoascus cerasi (Fckl.) Sad.] See Diseases of Orchards and Vineyards. Witches'-broom of birch (Species of Exoascus). See Dis- eases of Timbers and Timber Trees. Plum pockets and cherry pockets (Species of Exoascus, chiefly Exoascus pruni Fckl.). See Diseases of Orchards and Vineyards. Black-knot of plum and cherry [Ptowrightia morbosa (Scliia1.) Sac$.]. See Diseases of Orchards and Vineyards. Mold of mushrooms (Sporodinia grandis Link.). Mush- rooms of various kinds, wild as well as cultivated, are attacked by a mold of the bread- or black-mold group. The mold is particularly abundant on mushrooms that have been picked and kept in moist situations for some time. It lives chiefly as a saprophyte and forms on the mushroom a dense, white, moldy felt which is composed of comparatively coarse threads. This white felt later turns brown and then black. When in the brown state one usually finds an abundance of spore-cases, each containing several to many spores. When the felt has become black the sexual reproductive bodies are produced, similar to, but in much greater abundance than in, the ordinary bread mold. Their fusion results in the production of a thick-coated. 398 Minnesota Plant Diseases. resting spore. Shortly after the mold has become established decay of the mushrooms sets in and the latter may soon be de- stroyed. The trouble can usually be obviated by avoiding too moist conditions. There are several other molds of the bread- mold group which attack picked mushrooms. Gall fungus of the wild peanut (Synchytrium decipiens Farl.). This disease has no economical importance in Minnesota, since its host is an unused wild flower, but is of interest on ac- count of the fungus producing it. It is an exceedingly com- FIG. 211. — Gall fungus on the wild peanut. Minute galls can be seen on the petioles and leaflets. Original. mon disease and is often found in great abundance. The host plants then appear covered as with a yellow rust, not unlike the cluster-cup stages of a rust fungus. The fungus is a single- celled plant and lives in the cells of the host which it stimulates to an increased growth resembling tiny yellow galls. Swim- ming spores are produced in a manner similar to those of the seedling disease of cabbages. Winter spores are also formed in a similar manner to those of the cabbage disease. The fun- gus is abundant in rainy seasons. Fungus gall of wood anemone [Synchytrium anemones (DC.} Wor.]. This fungus is a similar plant to that of the wild Minnesota Plant Diseases. 390, peanut. It is single-celled and produces swimming spores in the early summer months. It forms small, dark, reddish galls in the tissues of the host plant, quite like those formed by the gall fungi of dandelion, wild peanut and cranberry, but the galls are colored red as in cranberry. This fungus is very common in Minnesota and is especially conspicuous in late spring and early summer. It can be readily recognized by the dark, reddish col- or of the host plant leaves and the small wart-like excres- cences. Leaf wart of dandelion (Synchytrium taraxaci DeBy. et Wor.}. This fungus is closely related to the fungus of the seed- ling! disease of cabbages. It attacks the leaves of the dandelion and stunts and distorts them. The fungus is a single spherical cell and lives in one of the epidermal cells of the host. The latter cell swells to many times its original size and produces the simplest kind of a plant gall. The leaf when badly infected contains many of these galls, so that the surface is more or less roughened by the abundance of warts. Swimming spores are produced in a manner similar to those of the seedling cabbage disease and spread the infection under moist conditions. Thick- coated winter spores are also produced. This disease, though not uncommon, is never serious enough to assist materially in getting rid of the dandelion pest. Cranberry scald (Undetermined fungi). The life stories of the fungi which cause this disease have not yet been worked out. There are probably several kinds producing what is com- monly known as scald. Small soft spots arise in the cranberry and these soft spots enlarge rapidly until the whole berry is af- fected and it now has the appearance of a scalded berry. The skin remains intact but the contents are watery and soft. In the diseased tissues one can find abundant threads of the fun- gus. The berry in later stages turns dark brown, finally shrivels and becomes black. On the surface are produced minute black spots appearing somewhat like the capsules of certain parasitic burnt-wood fungi. The disease appears in July and August and affects also cranberries in storage. Excessive moisture seems to favor the disease. Sanding of the bogs, an inch in depth, and draining in summer, so that they shall remain fairly dry, have been recommended. Inde x, Absorption, in fungi. 10 in parasites. 12 system of parasites, 10 threads, 61 Acetate of copper, 220 Acid of rancid butter, in potato wet rot, 340 Aecidium elatinum (Fig. 23), 53, 277, 27l grossularias, 317, 387 species of. 3$; Agaricacese (see gill fungi), 178 Agaricus campestris (Fig. 89), 179 melleus (Fig. 128), 260, 261, 262 melleus, mold on, 394 Age, of mycelium, 19, 20 old, predisposition of, 95 old, relations of, 91 stimulation, 83 Aid of state in disease preven- tion, 208 Albugo Candida, 330 Alcohol, in apple blight, 364 Alder, hairy pore fungus of, 259 powdery mildew of, 377 root tubercles of, 50 witches'-broom on, 121 Alfalfa, bacteria of, 196 leaf spot, 309 Algae, absence of rusts in, 165 blue green, 7 causing disease in plants, 198 flower pot, 104 partnership with fungi (Fig. 21), 48,49, I45» 146 pill box, host to Chytri- dines, 105 pond scums, 105 Algal fungi, 103, 104 destruction of small areas, 78 list of groups in, 104 lowly (Fig. 41), 104, 105 on animals, 66 on fruits, 65 Algal fungi, on insects, 67 Aluminum sulphate, Hassel- man's treatment, 239 Ammonia in blue water, 219 Ammoniacal copper carbonate, 219 for apple rot, 357 for aster leaf rust, 376 for black rot of vine, 366 for blight of ro^ 37^ for downy mildew 01 Deans, 33; for leaf blight of cder;, 321 for mildew of chrysanthe- mum, 380 for powdery mildew of ap- ple, 361 for powdery mildew of cu- cumber, 325 for powdery mildew of hops, 325 for powdery mildew of strawberry, 324 for powdery mildew of vines, 366 for rose leaf rust, 375 substitute for bordeaux, 220 Amoeba stage of slime moulds, 197 Amphibia, parasites on, 72 fish molds on, 107 Amphispore of Puccinia vexans, 159 Anatomy of host, effect of parasite on, 87 Ancestry of plants, Anemone, cluster-cup on (Fig. 74), 161 cup fungi on, 145 gall fungus of, 398, 399 host to Chytridines, 105 host to downy mildews, 112 rust of, 390 smut of, 392 Animals, burrowing, wounds caused by, 47 parasites on, 66 402 Minnesota Plant Diseases. Antagonisms of bacteria, 193 Anther-inhabiting parasites, 65 Anthers, smuts in, 158 Anthracnose, I51 of bean, 327 of currant and gooseberry, 327 of vines, 367, 368 Ants, parasites of, 71 Apiosporium, 394 Apparatus, fixings for spray (Fig. in), 228 Apples, bitter or ripe rot of (Fig. 190), '' 356,357 black rot of (Fig. 194), 363, 364 blight of (Fig. 195), 364,365 brown rot of, i 357, 358 cedar, of red cedar (Figs. 181, 182), 347, 348, 349 leaf rust of (Figs. 181, 182), 347, 348, 349, 350 powdery mildew of, 361 ripe rot of, 152 rot (Fig. 190), 356,357 rusts, 166 scab (Figs. 183, 184, 185, 186, 187), 138, 35i, 352, 353, 354 slime flux of, 271 Arcyria serpata (Fig. 100), 197 Armillaria mellea (Figs. 6, 128), 260, 261, 262 Aroids, rust of, 392 Arsenic mixtures 213, 214 Attack, methods of, in parasites, 61 Auriculariineae (see Jew's ear fungi). Ascomycetes, 117 Ash, leaf rust (Figs. 75, 76), 162, 163, 277 powdery mildew of, 395 Asparagus, rust of (Fig. 161), 166, 318, 319 spray pump for rust of (Figs. 109,110), 222,224 sterile fungus rot of, 329 Aspergillacese, 122 Aster, china, sterile fungus rot of, 329 Bacillus, a bacterial form, 190 amylovorus (Fig. 97), 193, 364, 365 of wet rot (Fig. 172), 340 Bacillus, sorghi, 314, 315 tracheiphilus (Fig. 173), 341 Bacteria (Fig. 96), 189 to 196 air-loving and air-shunning, 191 and iron ore, 191 apple and pear blight, 364, 365 assisting in fermentation, 119 assisting in wood rot, 40 bean leaf blight, 342 black rot of cabbage, 342 cause of disease, 189, 193 cause of plant disease, 192 classification of, 190 colorations by, 194 coloring matters of, 189 diseases in plants, 191 dye-forming, 194 fermentation by, 194 forms and sizes of, 189 general characters, 189 heat-loving, 192 in beer and wine, 196 in bread and beer making, 195 in cheese, 196 in slime exudations, 120 in slime flux, 271 in tanning, 196 influence of light, etc., on, 192 light and heat forming, 194 multiplication of, 190 nitrifying, 195 nodules of (Fig. 98), 195 of fire-blight of apples (Fig. 97), 193 of hay-curing and ensilage, 195 of rancid butter, 191 of root nodules (Fig. 99), 196 of vinegar, 191 partnerships and antagon- isms, 193 partnerships with plants, 50 pathologic, 193 phosphorescence of, 194 physiology of, 191 relationships, 189 rennet, 196 reproduction of, 190 sorghum blight, 314 spores of, 191 vinegar, 195 wet rot of potato (Fig. 172), 340 wilt of cucurbits (Fig. 173), 341 Minnesota Plant Diseases. 403 Bacteria, zoogloea, 190 Bacterial purple, 194 Ball-throwing fungus, explosive apparatus, 33 Balsam fir, green cup-fungus rot, 267 canker of stem, 268 Jews' ear fungus on (Fig. 79), 167 witches'-broom of (Fig. 23), 53, 277, 278 Barberry, rust spores on leaf (Fig. 73), 159 pycnidium on leaf (Fig. 74), 161 wheat rust on (Fig. 145), 283, 285, 290 Bark, tree, smooth shelves on, 171 Barley, covered smut of, 300, 302 ergot on, 130 naked smut, 300 rust (see rust of wheat). Barrel pumps (Figs. 104, 105), 213, 214, 230 in action (Fig. 107), 217 Basidiomycetes, 153 Basidium, of Jews' ear fungi (Fig. 78), 166 of palisade fungi (Fig. 81), 170 of rusts (Fig. 73), 159 of trembling fungi (Fig. 78), 166 of weeping fungi (Fig. 78), 166 true, 155 Basidium-bearing fungi, 153, 154. 155, 170 Bean, anthracnose of, 327 bacterial nodules of (Fig. 98), 195 downy mildew of, 112,336,337 leaf blight, 342 rust (Fig. 162), 166, 319 sterile-fungus rot of, 329 Bear's head fungus, 175 fruiting bodies of, 23 rot of timber, 244 Beefsteak fungi, 177 Beer, bacteria in, 196 Beer-making (see yeasts). bacteria in, 195 Bees' nest dwelling habit, 42 Bees' nest, fungi on, 122 Beet, damping-off of, 109 downy mildew of, 112, Jjp Beet, leaf spot of, 328 scab, 327 sclerotium disease of roots, 322 slime mold parasite of, 198 sterile-fungus rot of, 329 Beetle fungi, 139, 140 on insects (Fig. 30), 68, 69 origin of, 140 Beetles, parasites of, 71 Biologic species, 88 of rusts, 289 Birch, fungi on branches, 139 gill fungus on (Fig. 86), 177 green cup-fungus rot, 267 hairy pore fungus, 257 leaf rust, 279 parchment pore-fungus rot, 258 powdery mildew of, 125, 272, 377, 395 sapid fungus rot (Fig. 131), 265 shelf fungus, 175 slime flux of, 271 witches'-broom on, 56, 121, 271 Birch-fungus rot (Fig. 126), 254, 255 Birds, parasites on, 73 Bird's-eye rot of grape, 367 Bird's-nest fungi (Fig. 13), 186 fruiting bodies, 23 spore distribution, 29 Bird's-nest rust of red cedar, 350 Bird's-nest witches'-broom (Figs. 26, 57), 54, 55 Bitter rot of apples (Fig. 190), 356, 357 Blackberry, orange rust of (Fig. 160), 3i6,3i7 Black haw, powdery mildew of (Fig. 51), I25 Black knot (Fig. 59), 135, 136 allies of, 135, 136 fruiting bodies of, 23 on plum and cherry (Fig. 191), 358, 35'9, 36o Black fungi, 123 apple scab, 351 black rot of tomato, 329 black rot of vine, 3^5 early blight of potato, 329 imperfect fungi of, 149 red disease of mushrooms, 395 red knot rot, 271 404 Minnesota Plant Diseases. Black mold of clover (Fig. 153), 305 Black molds (Fig. 46), 113, 114 dung-dwelling habit (Fig. 16), 37 on food, • 43 on mushrooms, 397 parasites on, 114 soft rots of fruits, 353 Black rot of apple (Fig. 194), 363, 364 of cabbage (Figs. 174, 175, 176, 177, 178), 342, 343,344 of tomato, 328 of vine, 365, 366 Black rust of wheat (see rust- of wheat), 291 Black spot, on elm leaf, 136 on grasses, 136 Blight, early, of potatoes, 329 Blight, fire, of apples (Fig. 195), 364, 365 Blight, leaf, of celery, 328 Blight, of apples and pears (Fig. 195), 364, 365 of bean leaf, 342 of potato (Figs. 39, 166, 167), 99, 1 10, in, 112, 331, 332,333 of potato, epidemics, 100 of potato, inoculation by, 98 of potato, spores of (Fig. 44), 109 of rose (Figs. 203, 204), 378,379 of sorghum, 314, 315 of willow (Fig. 134), 272, 273 Blister of oak leaf, 272 Blow guns, 232 Blueberry, cup fungi on, 145 gall disease of, 385 gall fungi on, 170 galls on, 56 rust of, 387 Blue green algae in slime flux, 271 Blue molds (Fig. i), 122 allies of, 123 assisting in fermentation, 119 half saprophytes, 35 on food, 43 on mammals, . 73 parasites on, 115 relatives of, on bees' nests, 42 soft rots of fruit (Figs. 188, 189), 353 Blue molds, spore resistance to drying, 33 Blue water, 219 Board, pine, attacked by dry rot (Figs, 121, 122), 248, 249 Boletus, species of (Fig. 85), 176, 177 Bones, fungi on, 42, 122 Borage family, powdery mildew of, 396 wheat rust on, 283 Bordeaux (see bordeaux mix- ture), dry, 218, 227, 229 for anthracnose of currant, 327 for apple orchards, 347 for apple rot, 357 for apple scab, 352 for asparagus rust, 319 for bean anthracnose, 327 for bean rust, 319 for black knot, 360 for black rot of tomato, 329 for black rot of vines, 366 for blight of rose, 379 for brown rot of plums, 358 for carnation rust, 373 for downy mildew of cu- cumbers, 336 for downy mildew of onion, 334 for early blight of potatoes, 329 for leaf blight of celery, 328 for leaf blight of strawberry, 323 for leaf rust of apple, 349 for leaf spot of beets, 328 for orange rust of rasp- berry, etc., 317 for plum pocket, 362 for plum scab, 363 for plum leaf rust, 351 for potato blight, 333 for powdery mildew of ap- ple, 361 for powdery mildew of hops, 325 for powdery mildew of vines, 366 for rose leaf rust, 375 for rust of mallows, 373 for violet leaf spot, 381 Bordeaux mixture, 213, 215, 216, 217, 218 stock solutions of, 216, 217 Minnesota Plant Diseases. 405 Bordeaux mixture, test of, 216, 217 Bordeaux resin mixture, 218 stock solutions, 218 Botrytis vulgaris, 381 Brand of wheat, 297 Bread-niaking, bacteria in, 195 yeasts in, 36, 119 Bread molds (see black molds), //j, 114, 122 allies of, 66 on food, 43 on mushrooms. 397 Breeding act, in basidium-bearing fungi, 154 in fungi, 103 in rusts, 164 in sac fungi, 117 in water molds (Fig. 42), 106 in yeasts, 119 Bremia lactucae, 337, 339 Brewing, with yeasts, 36 Broccoli, black rot of, 342 Brome smut, 303 Broom (see witches'-broom). Broom corn smut, 300 Broom rapes, parasitic seed plants, 200 Brown rot of apples and plums, 357, 358 Brussels sprouts, black rot of, 342 Bucket pumps (Fig. 102), 211,230 Buckthorn, wheat rust on (Fig. 144), 283, 285.. 288 Building paper, fungi on, 137 Bulbs, bacteria in, 192 cup fungi on, 145 sclerotium disease of, 322 Burls on trees, 56 Burning of refuse, method of cure, 209 Burning, to prevent spread of disease, 207 Burnt-wood fungi, 139 apple rot, 356 fruit rots, 65 honey dew fungi, 394 on honey dew, 42 on leaves, 41 on log (Fig. 83), 173 on stems, 64 saprophytes on dung, 38 wound parasites, 47 Burreed elder (Fig. 45), in Butter, bacteria of rancid, 191 Buttercups, rust of, 386 Butterflies, parasites of, 69 Butyric acid in apple blight, 364 Cabbage, black rot of (see black- rot of cabbage). club root of (Fig. 180), 345, 346 downy mildew of, 331 host to Chytridines, 105 seedling disease of, 339, 340 sterile-fungus rot of, 329 white rust on, 330 Cake, molds on, 113 Calyptospora gceppertiana (Fig. 207), 387,389,390 Canary grass, ergot on (Figs. 54, 155), 128,308 Cancer roots, parasitic seed plants, 200 Cane sugar, yeasts in, 119 Canker of balsam fir stem, 268 Caper plants, white rust on, 330 Capillitium of slime mold (Fig. 100), 197 Capnodium, 394 Caps, reducing, for spray ap- paratus (Fig. in), 228 Carbonate, ammoniacal copper, 219 Carnation, rust, 373 smut, 158, 371, 393 Carrion fungi (Figs. 12,94,95), 29, 187, 188 earth-dwelling habit, 39 fruiting bodies, 23 spore distribution, 29 storage organs (Fig. 3), 15 strands of (Fig. 3), 16 Carrots, downy mildew of, 112 sterile-fungus rot of, 329 Catch flies, smut of, 371 Caterpillar fungi (Fig. 56), 130, 131, 132 allies of, 133 germinating spore (Fig. 15), 34 on animals, 66 on butterflies (Fig. 31), 69, 70 on insects, 68 storage organs, 15 Caterpillars, mold on, 115 406 Minnesota Plant Diseases. Cats, fungi on, 73 Cattle, fungi on, 73 wounds caused by, 47 Cauliflower, black rot of, 34^ sterile-fungus rot of, 329 Cause, immediate, of disease, 2 Cedar apple, of red cedar (Figs. 181, 182), 347, 348, 349 rusts of, 1 60, 164, 1 66 Cedar, red, bird's-nest broom of, 165 bird's-nest rust of, 350 Cedar, white, Jews' ear on, 167 Celery, leaf blight of, 328 sterile-fungus rot of, 329 Cells of wood tissues, 85 Cellulose, in cell walls, 85 Cercospora apii, 328 beticola, 328 violae, 381, 382 Cereal rusts (see rust of wheat). Cereal smuts, 158 Cereals, rust-proof varieties, 289 Chsetomiaceae (Fig. 60), 136, 137 Cheese, bacteria in, 196 green mold on, 118, 122 Cherry, black knot of (Fig. 191), 135, 136, 358, 359, 36o broom on, 56 brown rot of, 357 leaf rust of, 350 pockets of, 120, 361 powdery mildew of (Fig. 192), 360, 361 scab of, 363 stunting by pocket fungi, 82 witches'-broom of, 121, 271, 363 Chickens, parasites on, 73 Chickweed, rust of balsam fir, 278 Chlorosplenium seruginosum, 267 Chondrioderma difforme (Fig. i oo), I97 Chrysanthemum, powdery mil- dew of, 379, 380 rust, 371, 372 Chrysomyxa pirolse, 386 Chytridinese (Fig. 41), 104, 105 Cladosporium carpophilum, 363 Clamps, hose (Fig. in), 228 Clams, parasites of, 67 Classification of diseases, i Clavaria, species of (Fig. 83), 173 rots of wood, 244 Clavariaceae (Fig. 83), 172, 173, 174 Claviceps purpurea (Figs. 154, 155). 306,307,308,309 Cleanliness in prevention of spread, 207 Clover, bacterial nodules of, 195 black mold of (Fig. 153), 305 cup fungi on, 145 cup fungus leaf spot, 309, 310 damping-off, 109, 382 dodder on, 200 downy mildew of, 112, 314 leaf rust, 292 leaf spot of, 309, 310 rotation of crops and bac- teria, 196 rusts, 166 Clothes, mildew of, 43 Club fungi (Fig. 83), 172, 173, 174 earth-dwelling habit, 39 edible forms, 174 fruiting bodies, 23 rots of wood, 244 Club root of cabbage, radish, etc. (Figs. 179, 180), 345,346 Club root of beets, 198 Club rust of juniper, 349, 350 Cluster-cup, of ash-leaf (Figs. 75, 76), 162, 163 rust of composites, 387 rust of gooseberry and cur- rant, 317, 386, 387 rusts of wild flowers, 386 Coal spot diseases, 151 Coccus, a bacterial form, 190 Coelenterates, parasites of, 66 Coffee rusts, 166 losses by, 201 Coleosporium sonchi-arvensis (Fig. 205), 376, 388 Collards, black rots of, 342 Colletotrichum lindemuthianum, 327 Collybia rot, velvet stemmed (Fig. 130), 264,265 Collybia velutipes (Fig. 130), 264, 265 Colorations of bacteria, 194 Columbines, rust of, 386 Minnesota Plant Diseases. 407 Common gemmed puff-balls (Figs. 90, 91), 181, 182 Composites, powdery mildew of (Fig. 210), 396,397 powdery mildew of hops on, 325 rust of, 387 Cone-bearing trees, ring disease of, 270 Conifers, cup fungi on, 145 downy mildew of seedlings, 382 rust of cowberry, 390 sulphur fungus on, 253 Contract of parasitism in plants and animals, 75 Conversion of wood into punk, 19 Co-operation of state in disease prevention, 208 Copper acetate (dibasic), 220 substitute for carbonate, 220 Copper carbonate ammoniacal, 219 Copper saccharate, 220 Copper salts, effect on roots, 213 Copper sulphate, 219 for apple orchards, 347 for apple scab. 352 for powdery mildew of vines, 366 for rose leaf rust, 375 in blue water, 215 in bordeaux, 215 in Hasselman's treatment, 239 in saccharate of copper, 220 Coprinus comatus (Figs. 87,88), 178, 179 Coral fungus (Fig. 84), 174, 175 rot of woods (Fig. 119), 244,246 Coral root orchid, 10 partnership with fungus, 50 Cordyceps (Fig. 15), 34 Cordyceps militaris (Fig. 31), 70 stylophora (Fig. 31), 70 Coreopsis, sterile-fungus rot of, 329 Corn, broom, smut of, 300 Corn cockles, smut of, 393 Corn, rust, 292 Corn, smut (Figs. 148, 149), 156, 339 Gourds, downy mildew of (Figs. 1 68, 169, 170, 171), 334, 335, 336, 338 Grain smut of sorghum (Fig. 15*), 299 Grains, smuts on, 155, 158' Grape sugar, yeasts in, 119 Grape, anthracnose of, 367, 368 black rot of, 365, 366 diseases, losses by, 201 downy mildew of (Figs. 196, 197, 198), no, 112, 368, 369, 3?o< powdery mildew of, 125, 366, 367 root disease of, 138 Grass, canary, ergot on (Fig. 54), 128' ergots (Figs. 53, 54), 127, 128 family, downy mildew of, 112- pigeori, smut of, 394 rusts, 160 Grasses, ergot disease of (Figs. 154, 155'), 306,307,308,309 powdery mildew of (Fig. 152), 304 rusts of (see also rust of wheat), 165, 166 smothering fungus of, 306 smuts on, 158 strangling fungus of (Figs. 57, 58), 132, 133 Grasshopper, losses by, com- pared with wheat rust, 201 Green cup fungus rot, 267 Green felts, 9 Green islands, 84 Green molds, 122 Green mold, allies, 123 amateur parasites, 78 disease in man, 75 fruit rots, 44 on animals, 66 on food, 43 on cheese, 43, 118 rot of timber, 270 Greenhouse plants, diseases of, 371 Grey mold of lettuce, 381 Ground, Boletus on (Fig. 85), 176 cup fungi on, 142 puff-balls under, 184 morel allies on, 148 tooth fungi on, 175 Grubs, fungi on, 130, 131, 132 Guignardia bidwellii, 365, 366 Gymnoascaceae (Fig. 49), 121 Gymnoconia interstitialis (Fig. 160), 316,317 Gymosporangium clavariseforme, 349, 350 Minnesota Plant Diseases. 413 •Gymnosporangium, globosum (Figs. 181, 182), 347, 348, 349 macropus (Figs. 181, 182), 347, 348, 349 nidus-avis (Fig. 26), 57, 35° Habit, bee's-nest dwelling, 42 dung-dwelling, 37 food mold, 43 fungi on eggs, 44 fungus-dwelling, 42 honey-dew dwelling, 42 leaf-dwelling, 41 of parasites on anthers, 65 of parasites on fruit, 64 of parasites on leaves, 62 of parasites on stems, 63 of root parasites, 64 water mold, 36 wood dwelling, 40 yeast, 36 Hag fishes, degeneration in, 10 Hailstones, wounds caused by, 47 Hairy pore-fungus rot, 259 Half saprophytes, 35, 44 Hard-skinned puff-balls, 183 Hard woods, dry rot of, 245 Hasselman treatment of tim- bers, 239 Hausschwamm, 245 Haw, black, powdery mildew of (Fig. 51), 125 Hay-curing, bacteria of, 195 Hazel powdery mildew, 395 Head smut of sorghum (Fig. 150), 298, 299 Heat-forming bacteria, 194 Health, and disease, 2 improvements of, 91 in plants, defined, 90, 91 Heath family, partnership with fungus, 50 Heaths, gall fungi on, 170 gall disease of, 385 Helianthus, rust on, 373 Helvella lacunosa (Fig. 67), 148 Helvellinese (Figs. 67, 68), 146, 147, 148 Helotium citrinum (Fig. 65), 145 Hepatica, smut of, 392 Hole, shot, 151 Hollyhocks, rust of, 372, 373 Honey-colored mushroom, mold of> 394 rot (Fig. 128), 260,261,262 strands of (Fig. 6), 17 Honey dew, fungi, 125, 394 fungi, spore distribution, 29 -dwelling habit, 42 spores (Fig. 55), 128, 130 spores of ergot, 307 Honey mushroom, strands of, 16 Hoofs, blue mold allies on, 123 fungi on, 42 Hops, powdery mildew of, 324, 325 Horizontal pumps (Fig. ic8), 220, 231 Horn, blue mold allies on, 123 fungi on, 42 Hornbeam, hairy pore fungus on, 259 Horseradish, white rust on, 330 Horses, parasites of, 74 Host, effect of parasite on, 77 effect of parasite on anat- omy of, 87 effect on parasite, 88 infection, 97, 98 influence on spore germina- tion, 89 stimulation, 82 Hot water method, for loose smut of wheat, 297 for millet smut, 303 for naked and covered barley smut, 300, 303 for oat smut, 157 for smuts, 225, 226 for sorghum grain smut, 299, 300 House fungus rot (see dry rot). Hyalopsora polypodii, 387 Hydnaceas (Fig. 84), 174, 175 Hydnum coralloides (Figs. 84, 119), 174.246 Hymenogastracese (Fig. 81), 170 Hypochnaceae, 171 Hypocreaceae (caterpillar fungi), (Fig. 56), 130, 131, 132 (ergot fungi), (Figs. 53, 54), 128, 129, 130 (strangling fungi), (Figs. 57, 58), 132, 133 (in part), 133 Hypomyces lactifluorum, 395 Minnesota Plant Diseases* Hysteriine?e, 142 Immersion in solutions, methods of cure, 209, 210 Immunity and variation, 96 from disease, 93, 206 Impatiens, orange leaf-rust on, 291 Imperfect fungi (Fig. 70), 25, 26, 117, 149, 150, 157, 152 anthracnose of currant and gooseberry, 327 anthracnose of vines, 367, 368 bean anthracnose, 327 black rot of apple, 363, 364 flax wilt, 310 leaf blight of celery, 328 leaf habit of, 62 leaf spot of beets, 328 plum scab, 363 potato scab, 326 violet leaf spots, 381 wheat scab, 310 Impregnation of timbers to pre- vent rot, 239, 240 Increase in size, effect of para- sitism, 82 Indian, corn smut, tubercles of, 56 pipe, partnership with fun- gus, 50 turnip leaf-rust, 376, 392 Individuation, 51, 56 Infection, and prevention of dis- ease, 204 by wounds and prevention, 204, 205 conditions favoring, 98, 99 conditions of, 62 in parasitic fungi, 61, 62 in timber rots, 249 of grass leaf by a rust (Fig. 29), 61 of host, 97, 98 Inflorescences, smuts in, 158 Inheritance of disease, 94 Inky gill fungus (Figs. 87, 88), 178, 179 Inoculation of host, 97, 98 Insects, agents of spore distri- bution, 29 beetle fungi on, . 140 carrying slime mold of malaria, 198 carrying spores of bird's- nest fungi, 186 Insects, carrying smut spores, 65 carrying spores of ergot fungi, 128 causing witches'-brooms, 56 conditions of parasitism on (Fig. 30), 67,68 degeneration in, 10 distribution of spores by, 162 factor of disease, 92 fungi on (Fig. 56), 130, 131, 132 injuries to apple fruits, 355 molds (Fig. 47), 68, 1/5, 116 molds, on animals, 66 molds, on butterflies, 69 prevention of wounds by, 205 production of honey dew, 42 ravages by, 201 spore distribution in car- rion fungi, 187, 188 water molds on, 107 wounds caused by, 47 Interior-dwelling fungi, 61 parasites (Fig. 28), 60 Internal fungi, spraying of, 211 Iron ores, relation to bacteria, 191 Iron sulphate and sulphuric acid, 221 for anthracnose of grape, 367 for downy mildew of grape, 370 in Hasselman's treatment, 239 Isaria (Fig. 31), 70 Iva xanthiifolia, downy mildew of (Fig. 45), in Jells, molds on, 122 Jew's-ear fungi (Figs. 78, 79), 153, 154, 166, 167 Juniper, club rust of, 349, 350 Kainit, in Hasselman's treat- ment, 239 Kale, black rot of, 342 Kephir, bacteria in, 193 yeasts in, 119 Killing tissues, methods of, 79 Kinds of fruiting bodies of fungi (Fig. 10), 24 Kinds of fungi, basidium-bear- ing fungi, 153, 170 sac fungi, 117, 135 Knapsack pumps (Fig. 103), 212, 230 Knot black (Fig. 59), 135, 136 Minnesota Plant Diseases. 415 Knot, black, of plum and cherry (Fig. 191), 358, 359, 36o Knot of pine (Fig. 136), 275, 276 Knot, red, of currants, 322, 323 Kohlrabi, black rot of, 342 Kumys, yeasts in, 119 Labrador Tea, galls on (Fig. 37), 82,83,171 Laboulbeniineae, 139, 140 Larch, canker, European, 268 killed by parchment pore- fungus (Fig. 36), 81 parchment pore-fungus rot, 258 weeping fungi on, 169 Larva*, molds on, 115 Lead arsenate, for apple orch- ards, 347 Leaf blight of celery, 328 of strawberry, 323, 324 Leaf blister of oak, 272 Leaf curl, 120 fungi, and plum pockets, 362 fungi, witches'-broom of cherries, 363 fungi, leaf habit of, 62 Leaf, destroyers of, 80 -dwelling habit, 41 -dwelling fungi, agents of disintegration of debris, 41 fall of, caused by imperfect fungi, 152 green, absent from fungi, 7 -inhabiting parasites, condi- tions of, 62, 163 rust of apple and pears (Figs. 181, 182), 347, 348, 349 rust of ash, 277 rust of birch, 279 rust of clover, , 292 rust of pine, 276, 277 rust of plum, 350, 351 rust of rose (Figs. 199, 200, 201), 375 rust of willow (Fig. 138), 279 Leaf smut of onion, 320 of rye, 303 Leaf spot (Fig. 70), 149, 150, 151, 152 destroyer of small areas (Fig. 35), 78,79 diseases, 138 habit of, 62 of alfalfa, 309 Leaf spot, of beets, 328 of clover, cup fungus, 309, 310 of strawberry (Fig. 35), 79 of violets, 381, 382 Leaf wart of dandelion, 399 Leaves, rusts on, 164 tar spots on, 142 Leguminous plants, bacteria of, 196- Lentinus lepideus (Fig. 116), 236, 26? scaly, rot, 267 Lenzites abietina, 266 betulina (Fig. 86), 177 of pine, 266 Lepiota (Fig. 8), 20- procera (Fig. 18), 39 Lettuce, downy mildew of, 112, 337, 339- drop, 322, 380, 381 grey mold of, 380 sclerotium disease of, 322 sterile-fungus rot of, 329 Lice, plant, molds on, 116 Lichen (Fig. 21), 48- -forming fungi, 145, 146 Life methods of fungi, 35, processes in plants, 91 Light-forming bacteria, 194 influence on bacteria, 192 Lightning, wounds caused by, 47 Lignin, 40 action upon, by wood-dwell- ing fungi, 40 disintegration of, 85 in wood walls, 85. 86 Lilac, powdery mildew (Fig. 202), 125, 377 Lilies, rust of, 386 Lime and sulphur, for downy mildew of onion, 334 powder, 227 Lime, for club root, 346 for onion smut, 320 in bordeaux, 215 in dry bordeaux, 227, 228 in saccharate of copper, 220 potash of, in resin bordeaux, 218 Liquors, yeasts in, 119 Living together with special plant parts, 62 Localities, importance of, in prevention, 205, 416 Minnesota Plant Diseases. Locusts, molds on, 116 Log, club fungi on (Fig. 83), 173 coral fungus on (Fig. 84.), 174 pore fungi on, 175 rot of (see timber rots), -smooth shelves on, 171 trembling fungi on (Fig. 80), 167 weeping fungi on, 169 Lolium temulentum (Fig. 28), 60 Long-stalked puff-balls (Fig. 92), 182 Loose smut of oats (Fig. 146), 293, 294 of wheat, 297 of wheat, formalin treat- ment, 223 Loose-weft fungi (Fig. 49), 121 Lowly algal fungi (Fig. 41), 104, 105 gall fungus of peanut, 398 leaf wart of dandelion, 399 seedling disease of cabbage, 339, 340 Lucerne, downy mildew of, 314 leaf spot of, 309, 310 Lumber, rots of (see timber rots). Lumpy jaw of cattle, 73 in man, 75 Lurking fungi, 31 Lycoperdinese (Figs. 90, 91, 93), 184, 185, 186 Lycoperdon gemmatum (Figs. 90, 91), 181, 182 Macrosporium solani, 329 tomato, 328 Magnesium sulphate, for timber rot, 240 Malaria, slime mold of, 198 Mallow rust, 31, 166, 372, 373 Mammals, diseases of lower, 73 Man, agent of spore distribution, 31 fungus diseases of, 74 wounds caused by, 47 Manure, fresh, and spread of disease, 206 Maples, elm Pleurotus rot, 265 powdery mildew of, 125 slime flux of, 271 smothering fungus of seed- lings, 243 tar spots of leaf (Fig. 133), 142, 268, 269 Marsh mallows, 372 Mayflowers, rust of, 386 Meat extracts, fungi on, 122 Mechanical means of methods of cure, 209 Medicago denticulata, bacteria of nodules (Fig. 99), 196 Medusa-head fungus rot, 244 Melampsora betulina, 279 populina (Fig. 137), 278,279 salicis caprece (Fig. 138), 279 Melons, downy mildew of (Figs. 168 to 171), 112, 334, 335, 336 Merulius lacrymans (see dry rot) (Fig- 5), 15 Mildew powdery (Figs. 50, 51, 52), 124, 125 distribution of spores, 28 of apple, 361 of chrysanthemum, 379, 380 of composites (Fig. 210), 396, 397 of cucumbers, 324, 325 of elms (Fig. 135), 274 of gooseberry, 325 of grasses (Fig. 152), 304 of hazel, 395 of hops, 325 of lilacs (Fig. 202), 377 of mints, 397 of plums and cherries (Fig. 192), 360, 361 of rose (Figs. 203,204), 378, 379 of strawberry, 324 of vetch and crowfoot, 395, 396 of vines, 366, 367 of willow (Fig. 134), 272,273 Milk fungi, 179 sugar, yeasts in, H9 mushrooms, fungi on, 133 mushrooms, red disease of, 395. Milkweed rusts, 160, 386 Millet smut, 3°3 Minnows, fish molds on, 107 Mint, powdery mildew of, 397 rust of (Fig. 209), 1 60, 317, 318, 393- Method of attack in germinating spore, 19 of inspect-inhabiting fungi, 19 of parasites, 61 Minnesota Plant Diseases. 417 Methods for smut treatment, hot water, 225, 226 Methods of cure, 209 cleanliness, 209 prompt action in, 209 Methods of killing tissues, 79 Microsph?era alni (Fig. 202), 377 grossularia?, 325 Mildew downy (Fig. 44), 109, no, in of beans, peas, etc., 336, 337 of beets, 339 of clovers, 3T4 of cucumbers, melons, etc. (Figs. 1 68 to 171), 334, 335, 336, 338 of lettuce, 337, 339 of mustards, cabbage, etc., 331 of onion, 333, 334 of potato (Figs. 166, 167), 33i<332,333 of seedlings, 382 of spinach, 339 of vines (Figs. 196, 197, 198), 368, 369, 370 of violet, 384 Mildew, destroyer of organs, 80 epidemics (Fig. 40), 100, 101 leaf habit of, 62 of clothes, 43 of grapes, 112 Mistletoe, causing witches'- broom on spruce (Figs. 24, 25), 54-55 disease of spruce (Figs. 24, 25, 101), 54, 55, 199, 20°, 280, 281 Modes of life of parasitic fungi, 60 Molasses, in saccharate of cop- per, 220 Molds, 105, 1 06, 107, 113, 114, TT5, 122, 123 Molds, black, of clover (Fig. 153), 305 black or bread (Fig. 46), H3, H4 beginners in parasitism, 57 green, allies of, 123 green and blue, 122 green, rot of timber, 270 grey, of lettuce, 381 of honey-mushroom, 394 of insects (Fig. 47), 115, 116 Molds, of mushrooms, 397 on dung, 38 on eggs, 44 on mushrooms, 42 palisade fungi, 171 parasites of, 114 power of fermentation, 114 power to change sugar to starch, 114 rots on fruits, 64 sewer and drain (Fig. 43), 107, 108 slime (Fig. 100), 196, 197, 198 soft fruit rots, 353 water and fish (Fig. 42), 105, 106 Morchella esculenta (Fig. 66), 147 Morels (Fig. 66), 146, 147, 148 fruiting bodies of, 25 Morning glories, white rust of, 112 Mosquitos, molds on, 116 parasites of, 68 Moss, morel allies among, 148 parasites on, 198 cup fungi in, 144 Jew's-ear fungi on, 166 Mossworts, 165 Mucor, 353, 355 Mucorinese, black molds (Fig. 46), H3, H4 Mud puppy, fish molds on, 107 parasites on, 72 Museum of plant diseases, 209 Mushroom allies, on stems, 64 Mushrooms, basidium-bearing fungi, 155 coral fungus (Fig. 119), 244,246 earth-dwelling habit, 39 fairy rings, 20 fruiting bodies, 22 gill fungi (Fig. 89) 179 group, fungi on, 42 group, leaf dwellers, 41 group, wound parasites, 47 honey-colored, rot (Fig. 128), 260, 261, 262 honey-colored, mold of, 394 milk, fungi on, 133 molds on, 114, 397 on dung, 38 red disease of, 395 4i8 Mushrooms, spore distribution, 28 sulphur fungus, 253 true saprophytes, 35 truffles, 148 Muskmelons, downy mildew of (Figs. 1 68, 169, 170), 334 wilt of, 341 Mustard family, club root of, 345 damping-off of seedlings, 108, 382 downy mildew of, 331 Pythium debaryanum, 45 white rust of, 112, 330 Mycelium, definition of, 7, 8 development of, 18 of food mold (Fig. i), 8 of mushrooms, n physiology of, 17 Mycetozoa (Fig. 100), 196, 197, 198 Mycoplasm theory of rusts, 289 Mycorrhiza of puff-balls, 186 Mycosis, 73 Naked barley smut, 300 Nectria cinnabarina, 271, 272, 322, 323 Needle-cast of pines, 138 Nettles, sedge rust of, 391 Nidulariinere, 186 Nitrates, formation by bacteria, 195 Nitrifying bacteria, 195 Nitrogen-fixing bacteria, 195 Nodule bacteria, 195 Nozzle, for mist-like sprays (Fig. 114), 231 for spraying apparatus (Fig. in), 228 for spraying plants in rows, 230 for spraying under sides of leaves (Fig. 112), 230 Nuclear parasites, 66 Nutrition of fungi, 10 Nutritive method, expressed in structure, 9 Oak, Dsedalea on, 257 dry rot of, 245 false tinder fungus on, 250 fatty Pholiota rot of (Fig. 129), 263 fungi on limbs, 139 hairy pore-fungus, 259 leaf blister of, 272 Minnesota Plant Diseases. Oak, leaf curl fungi on, 121 partnership with fungus, 50 partridge wood rot of, 242 powdery mildew on, 125 rust of milkweeds on, 280 slime flux of, 271 Stereum wood rot (Fig. 117), 240 sulphur fungus on (Fig. 124), 252 white-piped and yellow- piped, 240 Oats, hot water treatment of, 157 loose smut of (Fig. 146), 293, 294 rust (Fig. 141), 285 smut of, 156, 157 smut of, an accomplished parasite (Fig. 27), 59 smut of, formalin treatment, 221, 223 Oidium, 150 chrysanthemi, j/p, 380 Oil, fish, in resin bordeaux, 218 Oil in resin prevention of rot, 240 Oils in ergot, 129 Old man's beard, rust of, 386; Olpidium brassicse, 339, 340 Onion, downy mildew of, 112, 333, 334 smut of, 158, 320 Oospora scabies (Fig. 164), 326 Orange leaf rust (see rust of wheat). rust of raspberries, etc. (Fig. 160), 316, 317 Orchard diseases, losses by, 202 spraying, horizontal pump for (Fig. 108), 220 trees, red knot on, 134 trees, wounds and preven- tion, 205 Orchards, diseases of, 347 Organisms causing disease, 189 Organs, destroyers of, 80 Ornamental plants, diseases of, 371 Oxalis, rust of corn, 292 Oyster fungus rot, 266 Palisade fungi (Fig. Si) 170 gall disease of blueberry, 385 wold, i/i Minnesota Plant Diseases. 419 Pansies, smut of, 371 Paper, building, fungi on, 137 moldy, fungi on, 137 Parasites (see also wound para- sites), 35, 5i cause development of floral rudiments, 83 cause increase in size of host, 82 cup fungi, 142, 144 defined, 9 destroyers of organs, 80 destroyers of small areas (Fig. 35), 78, 79 destroyers of whole plants, 80 effect of host on, 88 effect on anatomy of host, 87 effect on host, 77 effect on host tissues, 84 entrance through wounds, 45 formation of new organs, 84 higher seed plants, 199, 200 immediate destruction of host, 78 leaf inhabiting, 62 life methods, 60 low type of (Fig. 34), 77 on animals, 6<7 an anthers, 65 on birds, 73 on fruit, 64 on insects (Fig. 30), 67,68 on molds, 114 on nuclei, 66 on roots, 64 on special plant parts, on stems, 63 place, 198 plant, 77 rusts, 164 size of, * 13 stimulation of host, 82 stimulation of age, 83 surface dwelling, 60 wound, 235 Parasitic fungi, modes of life, 60 life of smut, 156 Parasitism, an auxiliary proc- cess, 200 and saprophytism, 12, 35 contrast in plants and ani- mals, 75 Parasitism, destructive, in animals, nutrient, proficiency in, 51 10 49 57,58 Parchment pore fungus rot, 258 Paris green, 213 for apple orchards, 347 Partnerships, fungi with alga?, 145 of bacteria, 193 of plants, equal (Fig. 21), 48 of plants, unequal, 49, 50, 51 Partridge wood rot (Fig. 118), 242 Pastry, molds on, 113 Pathologist, agent of preven- tion, , 208 Plicaria repanda (Fig. 64), 144 Pea family, powdery mildew of, 325 root tubercles of, 50 Peach, brown rot of, 357 Peanut, wild, gall fungus of (Fig. 211), 398 Pear blight (Fig. 195), 364,365 leaf rust of (Figs. 181, 182), 347, 348, 349 rusts, 166 Peas, downy mildew of, 336, 337 Penecillium (Figs. 188, 189), 353, 355 species of, 270 Peridermium, species of (Fig. 136), 275, 276 Permanganate of potassium, 221 Peronospora alsinearum (Fig. 44), 109 effusa, 339 leptosperma (Fig. 44), 109 parasitica, 331 schachtii, 339 schleideni, 333, 334 trifoliorum, 314 violse, 384 Peronosporinese (downy mil- dews), (Fig. 44), 109, no, ill (white rusts), 112 Pezizinea? (see cup fungi), 143, 144 Phacidiine^e, 142 Phallinece (Figs. 94, 95), 187, 188 Pholiota adiposa (Fig. 129), 262, 263 fatty, rot (Fig. 129), 262, 263 scurfy, rot, 263 420 Minnesota Plant Diseases. Pholiota, squarrosa, 263 Phosphorescence, bacterial, 194 Phragmidium speciosum, 375,376 subcorticuim (Figs. 199, 200, 201), 373 Phycomycetes, 104 Phyllachora trifolii (Fig. 153), 305 Phyllactinia suffulta, 395 Phyllosticta violae, 381, 382 Physiology of mycelium, 17 Phytophthora infestans (Figs. 44, 166, 167), 109, JJJ, 332, 333 omnivora (Fig. 44), 109, 382 phaseoli, 336, 337 Pigeon grass smut, 394 Pig-weed, white rust of, 112 Piling of timber, 238 Pilobolus (Figs. 16, 17), 37, 38 Pin worms, parasites of, 66 Pine board, attacked by dry rot (Figs. 121, 122), 248, 249 Pine knot (Fig. 136), 56, 82, 275, 276 Pine Lenzites, 266 Pine stem rust (Fig. 136), 275, 276 Pines, needle cast of, 138 ring scale of, 256 rust of leaves, 276, 277 rusts of wilkweeds and Pyrola, 386 stimulation in rusts of, 164 witches'-broom on (Fig. 22), 52 Pink family, rust of balsam fir, 278 smut of, 371,393 smut on anthers, 65 stimulation of floral rudi- ments, 83 stimulation of smuts in, 158 Pipe tongs, for spray apparatus (Fig. in), 228 Pitch-stemmed pore fungus rot, 259 Plant diseases, . go lice, molds on, 116 parasites of, 68 parasites, 77 partnerships, 48, 49 Plantain, powdery mildew of, 124 Plasmodiophora brassicse (Figs. !79, iSo), 345,346 Plasmodium of slime mold (Fig. 100), 197 Plasmopara cubensis (Figs 168 to 171), 334335,336,338 viticola (Figs. 196, 197, 198), 368,369,370 Pleurotus ostreatus, 266 rot of elm, 265, 266 sapidus (Fig. 131), 265,266 ulmarius (Fig. 20), 46, 265, 266 Pliers for spray apparatus (Fig. in), 228 Plowrightia morbosa (Figs. 59, 191), 135, 358, 359<36o Plug for spray apparatus (Fig. 111), 228 Plums, black knot of (Fig. 59), 135, 136, 358, 359, 36o brown rot of, 152, 357, 358 leaf rust of, 350, 351 pockets (Figs. 49, 193), 120, 121, 361, 362 pockets, oak leaf blisters, 272 powdery mildew of (Fig. 192), 360, 361 scab of, 363 stunting by pocket fungi, 82 witches'-brooms on, 121 Pockets, of plum and cherry (Figs. 49, 193), 82, 120, 121, 361, 362 Podosphaera leucotricha, 361 tridactyla (Fig. 192), 360, 361 Poisoning by ergot, 309 Poisonous gill fungi, 179, 186 pore fungi, 178 Poisons, corrosive sublimate, 226 in ergot, 129 smuts of grasses, . 295 use in methods of cure, 209 Poles, rot of, 239 Pollen, replaced by smut, 158 Polyporacese (see pore fungi). Polyporus betulinus (Fig. 126), 254, 255 picipes, 259 rot, zoned, 258 squamosus (Fig. 125), 254 sulphureus (Fig. 124), 252,253 Polystictus hirsutus, 259 pergamenus (Fig. 36), 81, 258 versicolor, 258 Pond scums, 9 Poplar rusts (Fig. 137), 160, 278, 279 Poplars, leaf and fungi on, 121 Minnesota Plant Diseases. 421 Poplars, powdery mildew of, 121, 125, 272 red knot on, 134 Pore fungi (Fig. 85), 175, 176, 177, 178 birch fungus (Fig. 126), 254, 255 creeping wood rot of, 258 currant rot, 320 dry rot fungus, 245, 247 to 250 earth-dwelling habit, 39 false tinder fungus, 250 flattened, rot (Fig. 123), 251,252 fruiting bodies, 23 hairy pore fungus, 259 oak Dsedalea, 257 zoned pore fungus, 258 on ground (Fig. 85), 176 on stems, 64 parchment, on larch (Fig. 36), 8 1, 258 pitch-stemmed, 259 ring-scale of pine, 256 root-rot of currant (Fig. 163), 321 scaly (Fig. 125), 254 sulphur fungus (Fig. 124) 252, 253 timber rots and wound parasites, 235 tinder fungus, 251 trametes radiciperda, 256 undetermined (Fig. 127), 257 wound parasites, 47 Portulaca, white rust of, 112 Potash of lime, in resin bordeaux, 218 Potassium permanganate, 221 Potassium sulphide, 220, 221, 357 for brown rot of plums, 358 for carnation rust, 373 for downy mildew of onion, 334 for mildew of chrysanthe- mum, 380 for powdery mildew of gooseberry, 325 for powdery mildew of rose, 379 for powdery mildew of vines, 366 Potato disease, losses by, 202 Potato blight (Fig. 39), 80, 99, no, in, 112 destroyer of leaves, 80 destructive effect, 78 distribution of spores, 27 epidemics, 100 spores of (Fig 44), 109 Potato, damping-off of seed- lings, 382 downy mildew of (Figs. 166, 167), 331, 332, 333 early blight of, fungus stimulation of tubers, scab (Fig. 164), scab, corrosive sublimate treatment, scab formalin treatment, starch, converted to sugar, sterile-fungus rot of, wet rot of (Fig. 172) Powder guns (Fig. 115), Powders, dry bordeaux, for dusting plants, sulphur, sulphur and lime, Powdery mildew (Figs. 50, 52), degree of parasitism, fruiting bodies, kinds of spores, of apple, 329 50 326 231, 226 223 114 329 340 232 227 227 227 227 51, 80. 124, 125 58 23 25 361 of chrysanthemums, 379, 380 of composites (Fig. 210), 396, 397 of cucumbers, 324, 325 of elms (Fig. 135), 274 of gooseberry, 325 of grasses (Fig. 152), 304 of hazel, 395 of hops, 325 of lilac, 377 of mints, 397 of plums and cherries (Fig. 192), 360, 361 of rose (Figs. 203, 204), 378, 379 of strawberry, 324 of vines, 366, 367 of vetch and crowfoot, 395, 396 of willow (Fig. 134), 272, 273 on limited areas, 79 spores of, 118 422 Minnesota Plant Diseases. Power pump, gear (Fig. 106), 216 Predisposition and variation, 96 factor in disease, 93 general and special, 93 kinds of 94, 95 Preserves, molds on, 122 Prevention of disease, 201 to 209 and fertilizers, 206 and state aid, 208 and wound infection, 204, 205 by spraying, 212 curative methods, 209 importance of localities, 205 importance of knowledge, 203 importance of co-operation, 203 plant pathologist in, 203 selection of varieties, 206 work of farmer in, 204 Prevention of dry rot, 250 of spread in disease, 207 of timber rots and tree diseases, 237, 238, 239, 240 Primrose, evening, rust of, 386 Proficiency in parasitism, 57, 58 Promycelium of rust (Fig. 73), 159 Prothallia, damping-off of, 383, 384 Protomyces, sucker threads (Fig. 2), ii Pruning, best time for, 205 for apple scab, 352 methods of cure, 209 of trees and protection, 237 wounds and treatment, 205 Puccinia angustata, 391 asparagi (Fig. 161), 318,319 caricis, 391 chrysanthemi, 371, 372 coronata (see rusts of wheat). fraxinata, 217 fusca, 390 graminis (see rusts of wheat), (Fig. 73), 159 menth^e (Fig. 209), 317,318, 393 pruni, 350,351 rubigo-vera (see rust of wheats). sorghi, 292 tanaceti (Fig. 206), 373, 374, 375, 3§9 vexans (Fig. 73), 159 violse, 373 Puff-balls and allies (Figs. 90 to 95), 153, 154, 181, 182 common gemmed (Figs. 90, 91) . 181, 182 earth-dwelling habit, 39 fruiting bodies, 23 hard skinned, 183 long stalked (Fig. 92), 182 spore distribution, 28 strands of, 16 true (Figs. 90, 91). 184, 185 underground, 184 Pumpkins, downy mildew of, 334 Pump, barrel (Figs. 104, 105), 213, 214, 230 barrel, in action (Fig. 107), 217 bucket (Fig. 102), 211, 230 complex type of spray (Figs. 109, no), 222, 224 engine power, 232 gear power, 231 gear power force (Fig. 106), 216 horizontal, 231 knapsack (Fig. 103), 212, 230 requirements for, 230, 231 Punk, 40 formation of, 85 Pseudomonas campestris (see black rot of cabbage). phaseoli, 342 Pseudopeziza medicaginis, 309 trifolii, 309, 310 Pure cultures of crops and epi- demics, 206 disadvantages, 205, 206 Pycnidium of wheat rust (Fig. 74), 161, 162 Pyrenomycetineae, 123 (dung fungi), (Fig. 60), 136, 137 (sphere fungi), 137, 138 (honeydew fungi), 125 Pyrola rust, 386 Pythium debaryanum (Fig. 34), 45, 77, 382, 383 intermedium, 383, 384 Quack grass, ergots of (Figs. 53, 155), 127,308 Rabbits, agents of spore distri- bution, 30 fungi on, 73 Radish, black rot of, 342 Minnesota Plant Diseases. 423 Radish, club root of, 345 sterile-fungus rot of, 329 white rust on, 330 Railway ties, gill fungus on (Fig. 116), 236 rot of, 87 Rag weed, powdery mildew of (Fig. 210), 396 Raspberries, orange rust of, 316, 317 Razoumofskya pusilla (Figs. 24, 25), 54< 55.280,281 Red cedar, witches'-broom on (Fig. 26), 54, 55, 57 Red disease of mushrooms, 395 Red knot. 134 of currants, 322, 323 rot, 271, 272 Red rust of raspberry, etc. (Fig, 160), 316,317 of wheat (see rust of wheat), 291 Red sea weeds, 9 Reed grass, ergot on (Figs. 53. 155)- 127,309 Reed mace fungus, 306 Refuse, burning of, methods of cure, 209 Rennet bacteria, 196 Reproduction of Fungi, 21 Reproductive, systems of para- sites, 10 Resin bordeaux for asparagus rust, 319 mixtures, 218 Rhizina inflata, 270 Rhizoctonia, species of, 329 Rhubarb, sterile-fungus rot of, 329 Rhytisma acerinum (Fig. 133), 268,269 salicinum (Fig. 133), 270 Rice, wild, ergot on (Fig. 155), 130,307,308 Ring disease of cone bearing trees, 270 scale of pine, 256 Rings, fairy, 18 Ripe rot of apples (Fig. 190), 356, 357 of fruits, 44, 353 Rocks, lichens on, 146 Root, hairs, fungus, 186 Root, -inhabiting parasites of, 64 nodules, bacteria of (Fig. 99), 196 parasites, seed plants, 200 • rot of currant (Fig. 163), 321 rot of trametes, 256 smut of sedge, 394 tubercles of pea family, 50 Roots, bacteria in (Fig. 98), 192, 195 rust on, 164 sclerotium disease of, 322 sphere fungi on, 138 sucker, of mistletoe, 200 Rose family, powdery mildew of hops or 321 leaf rust (Figs. 190. 200. 201), 375 powdery mildew of (Figs. 203, 204), 125, 378,379 stem rust, 375, 376 Rotation of crops and bacteria, 196 of crops, advantages of, 205, 206 Rot, black, of tomato, 328 brown, of potato tubers, 332 flattened pore fungus (Fig. 123), 251, 252 method of attack on wood cells (Fig. 38), 85,86 of apples, and plum, brown, 357, 358 of apples, bitter or ripe (Fig. 190), 356, 357 of apple, black (Fig. 194) 363, 364 of cabbage, black (see black rot of cabbage), of false tinder fungus, 250 of fruits, 44 of fruits, imperfect fungi, 152 of fruits, ripe, 353 of fruits, soft (Figs. 188, 189), 353, 355, 356 of fruits, storage, 353 of grapes, bird's-eye, 367 of root, trametes, 256 of scaly pore fungus (Fig. 125), 254 of shoe string fungus (Fig. 128), 260,261,262 424 Minnesota Plant Diseases. Rot, of sulphur fungus (Fig. 124), 252, 253 of timbers, dry (see dry rot), 235 of timbers, harvesting of trees, 237 of timbers, prevention of, 237, 238, 239, 240 of timbers, smooth shelf, 172 of timbers, trembling fungi, 169 of timbers, treatment to pre- vent, 239 of vine, black, 365, 366 of wood, coral fungus (Fig. 119), 244,246 of wood, stick fungi, 139 partridge wood (Fig. 118), 242 Stereum wood (Fig. 117), 240 sterile-fungus, of garden plants, 329 tinder fungus, 251 wet, of potato (Fig. 172), 340 Rush-like plants, smuts in, 158 rust of dark green, 391 Rust, bird's-nest of red cedar, 350 epidemics and pure cul- tures, 206 club, of juniper, 349, 350 leaf, of apples and pears (Figs. 181, 182), 347, 348, 349 of anemone, 390 of ash leaf, 277 of asparagus (Fig. 161), 318, 319 of asparagus, spray pump for (Figs. 109,110), 222,224 of aster leaf, 376 of bean (Fig. 162), 319 of birch leaf, 279 of carnations, 373 of cereals, losses by, 201 of chrysanthemums, 171, 372 of clover leaf, 292 of coffee epidemics, \oo of composites, 387 of corn, 292 of cowberry (Fig. 207), 387, 389, 390 of dark green rush, 391 of ferns, 387 of golden rod (Fig. 205), - 376, 388 Rust, of gooseberry and currant, 317, 386, 387 of grasses, destroyers of leaves, 80 of hollyhocks and mallows, 372, 373 of Indian turnip, 392 of mallow, epidemics, 98, 102 of milkweeds, 280, 386 of mint (Fig. 209) 317, 318, 393 of pine leaf, 276, 277, 351 of pine stem (Fig. 136), 275, 276 of poplar (Fig. 137), 278, 279 of Pyrola, 386 of rose leaf (Figs. 199, 200, 201), 375 of rose stem, 375, 376 of sedges, 391 of sunflower (Fig. 206), 373, 374, 375, 389 of violet, 373 of willow leaf (Fig. 138) 279 of wild sarsaparilla (Fig. 208), 390 orange, of raspberries, etc. (Fig. 1 60), 316, 317 predisposition towards, 93 -proof varieties of wheat, 289, 290, 291 spores, insect distribution, 29 white, inoculation by, 98 Rusts (Figs. 73, 74, 75, 7.6, 77), (see also page 166), 80, 159 to 166 breeding act in, 164 causing rupture of epi- dermis, 87 causing witches'-broom (Figs. 23,26), 51,53,57 cedar apples of red cedar (Figs. 181, 182), 347 cluster cup, of wild flowers, 386 effects of hosts on, 88 effects on tissues, 84 infection of grass leaf (Fig. 29), 6 i inoculation by spores, 98 leaf habit of, 62 of wheat (Fig. 73), 159 of wheat and other cereals (Figs. 139 to 145), 282 to 292 Minnesota Plant Diseases. 425 Rusts, of wheat, differences be- tween red and black rust, 291, 292 of wheat, epidemics, 100 of wheat, losses in Minne- sota, 201 of wheat, relation to varia- tion, 97 on limited areas, 79 producing pine knots, 82 proficiency of parasites, 59, 60 stimulation of new organs, 84 sucker threads (Fig. 2), n white, 112 white, of mustards, cab- bage, etc., 330 wind distribution of spores, 27 Rutabaga, black rot of, 342 club root of (Fig. 179), 345 Rye, ergot of (Fig. 154), 130, 307 leaf smut, 303 rust (see rust of wheat). Sac fungi, ///, 135 causing witches'-broom, 56 general characters, 103 Sac of cup fungus (Urnula), (Fig. 62), 141 Saccharate of copper, 220 Saccharomycetes (Fig. 48), 118, 119, 120 Saddle fungi (Fig. 67), 146, 147, 148 earth-dwelling habit, 39 Sago palms, alg;e in roots of, 198 Sake, yeasts in, 119 Sanitation, relation to bacteria, 192, 193 Sapid fungus rot (Fig. 131), 265, 266 Saprolegnia thuretii, 71 Saprolegniineae, 105, 106, 107, 108, 109 (Damping-off fungi), 108, 109 (Fish molds), (Fig. 42), 105, 106 (Sewer pipe molds), (Fig. 43), 107, 108 Saprophytes, 35 cup fungi, 142 definition of, 9 dung-dwelling habit, 37 earth-dwelling habit, 38 water-mold habit, 36 Saprophytes, yeast habit, 36 Saprophytism and parasitism, 12 Sarsaparilla, rust of wild (Fig. 208), 390 Scab of apple (Figs. 183, 184, 185, 186, 187), 138, 351 to 354 of apple, preparation for soft rots, 355 of apple, spores of (Fig. i87) 354 of beet, 327 of plum and cherries, 363 of potato (Fig. 164), 326 of potato, formalin treat- ment, 223 potato, corrosive sublimate treatment, 226 of wheat, 310 Scald of cranberry, 399 Scale, ring, of pine, 256 Scaly Lentinus rot, 267 pore fungus rot (Fig. 125), 254 Schinzia cypericola, 394 Sclerodermataceae, 183, Sclerotinia (Figs. 4, 63), 14, 143 fructigena, 357, 358- libertiana, 320, 322, 380, 381 Sclerotium disease of cucum- bers, 320. of ergot (Figs. 53, 54, 154, 155), 127, 128, 129, 307 Scotch pine (Fig. 136), 276 Scurfy Pholiota rot, 363 Sea weeds, red, breeding act, 140 Seasoning of timbers, 238 Sedge root smut, 394 rust, 391 Seed plants, higher, parasites, 199, 200 lower, 198 Seed wheat, from rusted fields, 290 Seedlings, damping-off of, 382, 383 disease of cabbage, 339, 340 downy mildew of (Fig. 44), 109, 382 smothering fungus of 243 Selection for special substances, 26 of hosts, fungus, 26 of varieties, 2 of varieties and disease prevention, 206 426 Minnesota Plant Diseases. Sewer pipe molds (Fig. 43), 107, 108 Shade trees, diseases of, 235, 260 wounds and prevention, 205 Shaggy-mane, fungus (Figs. 87, 83) 178, 179 spore distribution, 30 Shakers, pepper, 232 Shelf fungi, pore, 175 smooth (Fig. 82), 171 spore distribution, 28 Shepherd's purse, club root of, 345 white rust of, 112, 330 Shoe strings fungus, 16 rot (Fig. 128), 260, 261, 262 strands of honey mush- room (Fig. 6), 17 Shot hole diseases, 151 Shut-off for spray apparatus Fig. in), 228 Silkworms, parasites of, 71 Silver fir, broom of, 278 Slime flux fungi, 120 of trees, 271 Slime molds (Fig. 100), 7, 196, 197, 198 club root of turnips, etc., 345 parasites on plants, 198 plasmodium (Fig. 100), 197 Smooth shelf fungi (Fig. 82), 171 partridge wood rot, 242 smothering fungus of seed- lings, 243 Stereum rot, 240 Smothering fungus, (Fig. 82), 172 of grasses, 306 of seedlings, 243 Smut, covered, of barley, 300, 302 loose, of oats (Fig. 146), 293, 294 loose, of wheat, 297 naked, of barley, 300 of anemone, 392 of brome, 303 of broom corn, 300 of carnations, 371, 393 •of corn (Figs. 148, 149), 297,298 of corn, stimulation by, 158 of corn, treatment, 223 of grains, age of mycelium, 20 of millet, 303 Smut, of oats, an accomplished parasite (Fig. 27), 59 of oats, formalin treatment, 221, 223 of oats, hot water treat- ment, 157 of onion, 320 of pigeon grass, 394 of rye leaf, 303 of sedge root, 394 of sorghum head (Fig. 150), 298, 299 of sorghum grain (Fig. 151), 299 of violet, 393 of wheat, loose (Fig. 72), 157 of wheat, stinking, formalin treatment, 221, 223 spores, germinating (Fig. 7i), 155 spores, lurking, 31 spores, vitality, 33 spores, wind distribution, 27 stinking, of wheat. Smuts (Figs. 27, 71, 72, 146 to 151), 155, 156, 157, 158 accomplished parasites, 59 epidemics of, 100, 101 fruit rots, 64 half parasites, 35 host influence in germina- tion, 89 hot water treatment of, 225", 226 machines for treatment of, 232 on anthers, 65 on limited areas, 79 parasitic life of, 156 parasitic on roots, 64 predisposition toward, 94 proficiency of parasitism, 58 saprophytic life of, 156 treatment of, 33 Soap, in potassium permangan- ate, 221 Soapworts, smut of, 371 Soda lye, prevention of timber rot, 240 Sore throat, cause by yeast al- lies, 120 Soft rots of fruits (Figs. 188, J89), 353, 355, 356 Minnesota Plant Diseases. 427 Soft, woods, dry rot of, 245 Solomon's seal, false, rust of, 386 Solomon's seal, rust of, 386 Sordariacese (Fig. 60) 136, 13? Sorghum blight, 314, 315 grain smut of (Fig. 151), 299 head smut of (Fig. 150), 298, 299 rust on, 292 Spartina cynosuroides, 277 Spathula, downy mildew of, 339 Spontaneous combustion, bac- terial, 194 Sphaceloma ampelinum. 367, 368 Sphacelotheca reiliana (Fig. 150), 298, 299 sorghi (Fig. 151), 299, 300 Sphagnum, for prothallia, 384 Sphoerella fragarke (Fig 35), 79, 323, 324 Sphieriaceae, 137, 138 SphcErobolaceae, 183, 184 Sphaeropsis malorum (Fig. 194) 363, 364 Sph?erotheca castagnei, 324, 325 mors-uvse, 325 pannosa (Figs. 203, 204), 378, 379 Sphere fungi and allies, 137, 138 apple scab, 351 back rot of vine, 365 leaf blight of strawberry, 323, 324 Sphere-throwing fungi, 183, 184 Spiders, parasites of, 67 Spore, definition of 8, 21 germination of (Fig. 15), 18, 34 germination and seasons, 34 resting, germination, 34 succession, 26 Spores, distribution of, 26 distribution by animals, 30 distribution by insects, 28 distribution by water, 27 distribution by wind, 27 distribution, explosive ap- paratus (Fig. 14), 31 kinds of (Fig. 9), 21,22,25 kinds of, from one fungus (Fig. 11), 25 numbers of, 14 Spores, of algal fungi, 33 of apple scab, 354 of ash-leaf rust (Fig. 76), 163 of fish mold (Fig. 33), 72 of food mold (Fig. i), 8 saprophytes, 37, 38 of slime mold (Fig. 100), 197 of smuts germinating (Fig. 7i), 155 of water molds (Fig. 42), 106 of wheat rust (Fig. 73), 159 physiology of germination, 19 prodigality of, in fungi, 26 resistance to drying out, 33 resistance to temperature, 34 size and amount of nourish- ment, 26 swimming, 27 unfavorable conditions in germination, 26 Sporodinia grandis, 397 Sporidium of wheat rust (Fig. 73), 159 Spots, black, of grasses, 136 of leaf, of beets, 328 of leaves (see leaf spots), of violet leaf, 381,382 tar, 142 Spray apparatus (Figs. 102 to no), 2ii accessories, 231 fixings, tools, etc. (Fig. in), 228 good, 213 selection of, 229, 230 special, 231 Spray pump, complex type (Figs. 109, no) 222, 224 Spraying, a check to epidem- ics (Fig. 40), 101 a preventive method, 209 action of, 211 of fungi, best time for, 27 of plants, value of, 212 plants in rows (Fig. 112), 230 under sides of leaves (Fig. 112), 230 Sprays, 215 ammoniacal copper car- bonate, 219 bordeaux, 215 428 Minnesota Plant Diseases. Sprays, , bordeaux resin, 218 copper acetate, 220 copper sulphate, 219 eau celeste, 219 iron sulphate and sulphuric acid, 221 potassium permanganate, 221 potassium sulphide, 220 saccharate of copper, 220 Spread of diseases, prevention of, 217 Spruce, mistletoe disease of (Fig. 101), igg, 200, 280, 281 rust of cowberry, . 390 witches'-broom on (Figs. 24, 25), 54, 55 Squash, downy mildew of, 334 wilt of (Fig. 173), 341 Squirrel, agent of spore distri- bution, 330 corn, rust of, 386 tail grass, rust on, 287 wounds caused by, 47 Stalked fungi (see basidium- bearing fungi), 103 Stalked puff-balls (Fig. 92), 182, 183 strands of (Fig. 3), 13 Starch, molds on, 122 solution of, by fungi, 85 turned to sugar by molds, 114 yeasts in, 119 Stars, earth (Fig. 93), 185, 186 Starworts, smut of, 371 State aid in disease prevention, 208 Steeps, 221 corrosive sublimate, 226 formalin, 221, 223 hot water, 225 Stem canker of balsam fir, 268 -inhabiting parasites, 63 rust (see rust of wheat), rust of cowberry (Fig. 207), 387, 389, 390 rust of pine (Fig. 136), 275, 276 rust of rose, 375, 376 Stems, bacteria in, 192 dead, cup fungi on, 144 imperfect fungi on, 152 rusts on, 164 smuts in, 158 sphere fungi on, 138 Stereum frustulosum (Fig. 118), 242 hirsutum, 240 wood rot (Fig. 117), 240 Sterile-fungus rot of garden plants, 329 Sticks, dead, cup fungi on, 144 dead, fungi, 139 fungi on, 134 gill fungus on (Fig. 86), 177 tar spot allies on, 142 trembling fungi on, 169 Stimulation by rusts, 164 by smuts, 158 of floral rudiments, 83 of host, 82, 171 of new organs, 84 Stinking smut of wheat (Fig. 147), 295, 296 formalin treatment, 221, 223 Storage organs (Figs. 3, 4), 13, 14, 15 caterpillar fungi. 131 food material of, 15 of cup fungi, 145 of ergot (Figs. 53, 54), 127, 128, 129 with fruiting bodies (Fig. 4), 14 Storage rots of fruit, 353 Strainer brass, for barrel pump (Fig. 105), 211 Strands (Fig. 3), 13 of dry rot (Fig. 5), 15 of honey mushroom (Fig. 7), 18 of puff-ball (Fig. 93), 185 Strangling fungi (Figs. 57, 58), 132, 133 Strawberry leaf blight, 323, 324 leaf spot (Fig. 35), 79, 138 powdery mildew of, 324 Stumps, rots of (see timber rots). Stunting of plants, 81, 82 Sublimate corrosive, a steep, 226 Sucker roots of mistletoe and dodder, 200 Sucker threads of parasitic fungi (Fig. 2), 61 Sugar, from starch by molds, 114 yeast in solutions of, 119 Sulphate, iron, and sulphuric acid, 221 Minnesota Plant Diseases. 429 Sulphate, of iron copper and alum- inum, 239 of magnesium, 240 Sulphide of potassium, 220 Sulphur and lime, 227 for downy mildew of onion, 334 Sulphur for asparagus rust, 319 for onion smut, 320 for powdery mildew of cu- cumber, 325 for powdery mildew of rose, 379 for powdery mildew of strawberry. 324 for powdery mildew of vines, 366 flowers of, 227 fungus (Fig. 124), 175,^52, 25 3 Sulphuric acid and iron sul- phate, 221 for anthracnose of grape, 367 Sumacs, leaf curl fungi on, 121 Sun scalds, wounds of, 47 Sunflowers, downy mildew of, 112 powdery mildew of, 396 rusts of (Fig. 206), 160, 373, 374, 375, 389 Susceptibility toward disease, 206 Sweet William, sterile-fungus rot of, 329 Swimming spores of fish mold (Fig. 33), 72 Synchytrium anemones, 398, 399 decipiens (Fig. 211), 398 taraxaci, 399 Tamaracks, scaly Lentinus rot, 267 Tanning and bacteria, 196 Tape worms, degeneration in, 10 Taphrina, species of, 272 Tar ringing, to prevent insect wounds, 205 spots and allies, 142 spots of maple (Fig. 133), 268, 269 spots of maple and willow, 136 spots of willow (Fig. 133), 270 to cover wounds, 205 used against timber rot, 87 Temperature, influence on bac- teria, 192 Terfeziaceae, 123 Texas fever of cattle, slime molds of, 198 Thalictrum, rust of, 390 Thelephora laciniatum, 172, 243 terrestris, 243 Thelephoracese (Fig. 82), 171 Thorn trees, leaf rust of, 349 Threads, sterile, in cup of cup fungi (Fig. 62), 141 sucker, 61 Thrush, caused by yeast allies, 120 Ties, railroad, gill fungus on (Fig. 116), 236 railroad, rot of (Fig. 116), 87, 236, 239 Tilletia tritici (Fig. 147) 295, 296 Timber rots, 235, 260 birch-fungus, 254 bird's-nest fungi, 187 club fungus, 244 coral fungus, 244 creeping pore fungus, 258 dry rot, 245 elm Pleurotus, 265 false tinder fungus, 250 fatty Pholiota, 262 flattened pore fungus, 251 gill fungus, 179 green cup fungus, 267 green mold. 270 hairy pore fungus, 259 methods of attack upon wood cells (Fig. 38), 85,86 Nectria of red knot, 271 oak Dsedalea, 257 parchment pore fungus, 258 partridge wood rot, 242 pine Lenzites, 266 pitch-stemmed pore fungus, 259 prevention of, 237, 238, 239, 240 ring scale of pine, 256 scaly Lentinus, 267 scaly pore fungus, 254 scurfy Pholiota, 263 shoe string fungus, 260 smooth shelf, 172 Stereum wood rot, 240 sulphur fungus, 252 tinder fungus, 251 Trametes wood rot, 256 use of cresote to prevent, 239 43° Minnesota Plant Diseases, Timber rots, velvet stemmed Collybia, 265 zoned Polyporus, 258 see also Chapter XVI. and XVII. Timber trees, red knot on, 134 disease of, 235 Timbers, basidium-bearing fungi on, 154 conditions of rotting, 87 creosoting, 87 dry rot of (see dry rot), impregnation of, to prevent rot, 239 house, rots of, 235, 245, 247, 248, 249, 250 piling of, 238 pore fungi on, 175 seasoning of, 238 sphere fungi on, 138 storing of, 238 tooth fungi on, 175 treatment of, to prevent rot, 239 trembling fungi on, 169 ventilation of, to prevent dry rot, 250 wood-dwelling fungi on, 40 Tinder-fungus rot, 177, 251 false, 250 Tissues, effect on, by parasites, 84 methods of killing, 79 Toad flax, parasitic seed plant, 200 Toad stools, fruiting bodies, 22 Tobacco plants, downy mildew of, 112 Tomato, black rot of, 328 disease, losses by, 201 Tomatoes, host to downy mil- dew, 112 Tools, fixings, etc., for spray apparatus (Fig. in), 228 Tooth fungi (Fig. 84), 174, 175 coral fungus, 244 Toxins, bacterial, 193 Trametes pini, 256 radiciperda, 256 root rot, 256 Treatmentj for smuts, hot. water, 225, 226 of apple orchards, 347 of timbers to prevent rot, 239 Tree diseases, prevention of, 237, 238, 239, 240 Trees, conifers, cup fungi on, 145 diseases of, 235 harvesting of, 237 slime flux of, 271 Tree trunks, lichens on, 146 Trembling fungi (Figs. 78, 80), 153, 154, 167, 168, 169 basidium (Fig. 78), 166 Tre.mella (Fig. 80), 168 Tremellinese (see trembling fungi). Trifolium incarnatum, black mold of, 306 Triphragmium clavellosum (Fig. 208), 390 True puff-balls (Figs. 90, 91), 184, 185 True truffles (Figs. 68, 69), 148, 149 Truffles, 117 false, 123 fruiting bodies, 23, 25 spore distribution, 30 true (Figs. 68, 69), 148, 149 Trunk, tree, cup fungi on, 144 tree, smooth shelves on, 171 Tuber lyoni (Figs. 68, 69), 149, 150 Tuberculosis, bacteria of, 193 Tuberineae (Figs. 68, 69), 148, 149 Tuckahoe Indian bread, 15 Tulostoma mammosum (Fig. 92), 183 Tulostomaceae (Figs. 3, 92), ^ 182 Tunbridge nare, 267 Turnip, black rot of, 342 club root of (Fig. 179), 345' Indian, rust of, 392 sclerotum disease of roots, 322 white rust on, 330 Tylostoma (see Tulostoma). Typhoid, bacteria of, 193 Uncinula, macrospora (Fig. 135), 274 necator, 366, 367 salicis (Fig. 134), 272,273 Underground puff-balls, 184 Uredinese (see rusts), Urnula craterium (Figs. 61, 62), 140, 141 Urocystis, anemones, 392 Minnesota Plant Diseases. Urocystis, cepulae, 320 occulta, 303 violse, 393 Uromyces, appendiculatus, 319 caladii, 392 caryophyllinus, 373 trifolii, 292 Ustilaginese (see smuts). Ustilago, avense (Fig. 146), 293, 294 bromivora, 303 crameri, 303 hordei, 300, 302 maydis (Figs. 148, 149), 297, 298 neglecla, 394 nuda, 300 tritici (Fig. 72) 157, 297 violacea, 371, 393 Variation and predisposition, 96 relation to disease, 91 Varieties, rust-proof, 97 selection of and prevention of disease, 96, 206 Vegetable worms, 16 Velvet-stemmed Collybia rot (Fig. 130), 264, 265 Venturia pomi (Figs. 183, 184, l85), 35i< 352, 353 Verbena, powdery mildew of 396 Vertebrates, degeneration, 10 Vetch, powdery mildew of, 395, 396 spring, bacteria of nudules (Fig. 99), 196 Vicia sativa, bacteria of nodules (Fig. 99), 196 Vinegar bacteria, 191, 195 Vines, anthracnose of, 307, 368 black rot of, 365, 366 downy mildew of (Figs. 196, 197, 198), 112, i lo, 368, 369, 370 powdery mildew of, 366, 367 Vineyards, disease of, 347, j6.5 Violet, cluster cup rust of, 386 downy mildew of, - 112,384 rust, 373 smuts of, 158, 371, 393 spot of leaf, 381, 382 sterile-fungus rot of, 329 Wall flower, white rust on, 330 Water cress, white rust on, 330 Water, flea, parasites of, 67 hot, method for smuts, 225', 226 molds (Fig. 42), 105, 106 molds, distribution of spores, 27 molds, on animals, 66 molds, on crabs, 67 molds, on fish, 71 molds, saprophytic habits, 36 Watermelons, downy mildew of 334 Weeping fungi (Fig. 78), 153, 154, 169, 245 basidium of (Fig. 78), 166 Wet rot of potato (Fig. 172), 340 Wheat, brand, 297 crop rotation and bacteria, 196 ergot of, 130, 307 formalin treatment of stink- ing smut, 221, 223 loose smut of (Figs. 71, 72), 155,157,297 loose smut of, formalin treatment, 223 Wheat rust (see also rusts of wheat), 10 (Figs. 73, 74), 159, 163 to 166 and variation, 97 distribution of spores, 27 epidemics and pure cul- tures, 100, 206 host succession, 26 infection of grass leaf (Fig. 29), 61 kinds of spores (Fig. n), 25 scab, 310 stinking smut of (Figs. 71, 147), 155, 295, 296 White cohosh, rust of, 386 piped oak, 240 rusts, formation of leaf green in petals of hosts flower, 85 rusts of mustards, cabbage, etc., 330 Wild flowers, cluster cup rusts of, 386 Wild mushrooms (Fig. 89), 180 Wild rice, ergot on, 130 Willow blight (Fig. 134), 272, 273 leaf rust (Fig. 138), 279 432 Minnesota Plant Diseases Willow, powdery mildew of (Fig. 52), 125, 126 rusts, 160 tar spots (Fig. 133), 142,^70 Wilt of cucurbits (Fig. 173), 341 of flax (Figs. 156, 157, 158, 159), 3io to 314 Wind, assistance in infection, 98 spore distribution in puff- balls, 182 Wine, bacteria in, 196 Witches'-broom (Fig. 22), 51, 52 age of mycelium, 20 caused by insects, . 56 caused by leaf curl fungi, 121 of rust origin, 164 on balsam fir (Fig. 23), 153, 277, 278 on birch, 56, 271 on cherry, 56, 363 on red cedar (Figs. 26, 57), 54, 55 on spruce (Fig. 101), 199, 200 on white spruce (Figs. 24, 25, 55), 54 stunting in age, 82 Witches' butter, a trembling fungus, 169 Wood, attacked by fungi, 40 basidium bearing fungi on, 154 bird's-nest fungi on, 186 characters of, 85' dead, cup fungi on, 142 -destroying fungi, action on lignin (Fig. 38), 85,86 -dwelling fungi, action on wood, 40 -dwelling fungi, methods of entrance, 40 -dwelling fungi, nutrition, 40 -dwelling habit, 40 gill fungi on, 179 Jew's-ear fungi on, 166 palisade fungi on, 171 -peckers, agents of spore distribution, 31 -peckers, wounds caused by, 47 rot, coral fungus (Fig. 119), 244, 246 rot, destruction of wood (Fig. 38), 86 Wood, rot, creeping pore fungus, 258 rot, partridge (Fig. 118), 242 rot (see also timber rots), rot, Stereum (Fig. 117), 240 sphere throwing fungi on, 184 tissues, 85 tooth fungi on, 175 trembling fungi on, 167 Worms, degeneration in, 10 true, parasites of, 67 Wound infection and prevention of disease, 204, 205 parasites (Fig. 20), 45, 46, 80, 235 parasites, birch fungus, 255 parasites, degree of para- sites, 58 parasites, destroyers of branches, 80 parasites, false tinder fun- gus, 250 parasites, gill fungi, 179 parasites, ring scale of pine, 256 parasites, scaly pore fungus, 254 parasites, Stereum (Fig. 117), 241 parasites, sulphur fungus, 253 parasites, tinder fungus, 251 Wounds, cause of, 47 causes of predisposition, 96 in bark, entrance of rots, 41 in bark, causes, 41 Yeast-like fungi on animals, 66 on man, 75 on water flea, 67 Yeasts (Fig. 48), 118, 119, 120 allies of, 120 fermentation, 36 habit of saprophytes, 36 in bread making, 119 in slime exudation, 120 in slime flux, 271 occurrence in nature, 36 power of fermentation, 119 Yellow piped oak, 240 Youth, predisposition of, 95 relation to disease, 91 Zinc chloride, to prevent tim- ber rot, 239 Zoned Polyporus rot, 258 Zoogloea, 190 THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. LD 21-100m-8,'34 881278 73 / BIOLOGY LIBRARY G THE UNIVERSITY OF CALIFORNIA LIBRARY