sith sh -* Recast sta? oo re Gas Ob 75/ ceo lie, AA 2? eae Copyright N° COPYRIGHT DEFOSE: PabORATORY OUTLINES IN PLANT PATHOLOGY BY H. H. WHETZEL Professor of Plant Pathology LEX R. HESLER CHAS. Ty GREGORY Assistant Professor of Plant Pathology Assistant Professor of Plant Pathology W. HOWARD RANKIN Assistant Professor of Plant Pathology NEW YORK STATE COLLEGE OF AGRICULTURE AT CORNELL UNIVERSITY ITHACA, Nox £OT6 PUBLISHED BY THE AUTHORS COPYRIGHT, 1916 H. H. WHETZELL -_— set ae OCT 30 1916 * W. F. Humphrey, Printer, Geneva, N. Y. ©cra445394 © PREFACE acquainting the student with the laboratory materials presented in this course. They are the result of several years of experience and test in actual practice work. They have been frequently revised. It is expected that they will now be revised and reprinted at least every two years. Although the acquisition of a body of facts is an important and neces- sary part of the work in such a course a more vital feature is the training in logical methods of acquiring them. The student is urged to follow his outline carefully, making sure at each step, that the outline and the materials before him agree. ‘The same sequence of treatment is followed throughout all the outlines. This sequence in procedure should be mast- ered promptly. The term papers will afford opportunities for determining how well the student has grasped the logic of this procedure. The grouping of diseases here presented is, we believe, an important step in diverting attention from the domination of systematic mycology in phytopathological teaching and writing, and of directing it toward the more logical classification and study of diseases on the basis of the pathological phenomena exhibited. At the same time the subgrouping of the diseases, according to the chief etiologic factor involved, provides for a point of view still generally presented in the teaching of plant path- ology. It is not expected that all the diseases herein outlined will be covered in a three hours’ course. The instructor will make such selections from the different groups as will best serve his purpose in illustrating the funda- mentals of the subject in the case of the students in his classes. No laboratory practice in the methods of control of the diseases studied is provided. That phase of the subject is fully treated in the course based upon and following this, namely, The Principles of Plant Disease Control. These outlines are designed specifically for the work as given at Cornell University and without any attempt to adapt them for use in other institu- tions. It is hoped, however, that teachers elsewhere may at least find them helpful and possibly usable in their classes. Acknowledgments are due Mr. Chas. Chupp, instructor in the depart- ment of Plant Pathology for the preparation of a number of the outlines. We also gratefully acknowledge the friendly advice and assistance of the Comstock Publishing Company in our effort to make the cost of these outlines to the student as reasonable as possible. / ‘HESE outlines are designed solely for the purpose of most effectively \ THE AUTHORS. CONTENTS ; PAGE ieldie (rip: ssi ceee neces as EMOTO GOIDISE OIC CE EOI ee eae a Witeratuneror PlanteWiseases! % 4.520 .se%n s She ste © Seal ae Senso eele eis 10 NECROTIC DISEASES Caused by bacteria EYDRE, EF ie Sy ea Len SN eT re 15 Streak of Sweet Peas ............. NTRS CIE Olin GORA Se Soon eee 19 TByervay J Bie of ee, alee eA rch a Bibs sei ha SES cae ee ae een ee em ee 21 Vie kag ern NS PA TOLLE See cee ici aL an atattc Saleh) Gye 0.545 Nis alo disisie sy vol Slew aveievla 23 EAL OVO SOU le ORI eid ois tale's Seine aici s — 15. That the conidiophores cover the entire under surface of the leaves. Where this occurs, one may be quite sure it is a case of “‘sys- temic infection’’ and not a local lesion. If fresh material is available, make sections through some part of systemically infected plants (crown or rootstock). Stain with methyl blue, wash thoroughly, cover and locate the mycelium in the tissues; inter- or intracellular’? Haustoria? DRAW. The mycelium continues to live in the gradually weakening host, pro- ducing one crop of conidia each season from which primary infections, local or systemic, in character may arise. It eventually perishes with the host. REPORT 1. If a gardener discovered some of his perennials to be suffering from systemic infection, what methods of control should he employ? Why? If all the infections are local, what should be the treatment? Why? 2. Show in a graphic diagram the life-cycles of either of the pathogenes studied in this exercise. POWDERY MILDEWS OF FLORISTS’ CROPS Powdery mildew diseases frequently affect various ornamental plants of greenhouse and garden. They are sometimes very destructive and commonly troublesome. Among such plants which most often suffer from the powdery mildews are roses, phloxes, sweet peas, willows, hawthorns, lilacs, honeysuckles, bittersweet and dogwoods. SYMPTOMS The leaves are usually the organs affected, although stems, blossoms and even fruits may be diseased. Powdery mildews are usually most common and conspicuous in gardens and borders toward the latter part of the season. The white mealy coating which is formed on the affected organs is usually very striking. ‘The minute black perithecia of the patho- gene frequently appear in great numbers late in the summer or early au- tumn, in some cases standing out sharply against the white mycelial mats on which they rest. Where the mycelium is sparse or webby, the black perithecia may not be easily detected. In many cases they are but rarely formed. A tendency to stunt or dwarf the host is commonly to be ob- served. This is much more striking in some cases than in others. On the rose. Examine the diseased shoots provided. OBSERVE:— 1. The white felt, covering large areas on the canes and running out over the thorns; in some cases localized about the base of large thorns. 2. The powdery and less felty character of the white coating of the leaves. Which surface is affected? 3. The curling and dwarfing effect on the leaves, especially marked in hothouse-roses and in ramblers. 4. The abnormal coloration sometimes exhibited by the leaf under and about the mildewed spot. 5. The dwarfing of the entire tips or branches of some shoots, most frequently observed in ramblers. This results from bud-infection explained later. 6. The white mycelial felt, coating young buds and hips. The buds are often so stunted that they fail to open or the affected hips are dwarfed and do not ripen. Make pRAwINGs to show the symptoms exhibited in the material studied. On phlox. All above-ground parts of this host are likely to be affected. The mildew-spots are most prominent on the leaves. Examine the speci- mens provided. OBSERVE:— 7. The felty white mycelial patches on the leaves. How do the patches on the two surfaces of the leaf differ? 8. The purple coloration often developed beneath and about the spots. 9. The yellowish color of the mycelial mat in the older patches and their tendency to coalesce and cover the larger part of the leaf-surface. 10. The brown centers of many of the spots due, as may be seen with the hand-lens, to the perithecial fruit-bodies of the pathogene. 11. The mycelial patches on stems and inflorescence; less felty, often hardly discernible but usually covered with the brown perithecia. ny 118 12. The dwarfing effect on the inflorescence. Flowering is often partially or entirely prevented. Make a series of DRAWINGS to show the symptoms exhibited by mildewed phlox. On peas. Both sweet peas and garden- or field-peas are affected. Examine the material provided and NoTE:— 13. That the mycelial coating spreads almost uniformly over the entire leaf-surface, stems and pods. 14. That it is much thinner than that on rose or phlox, and is web-like instead of felty. 15. That there is little difference in the character of the mycelial coating on the upper and lower surfaces of the leaf. 16. The general effect on the growth of the plant. Is dwarfing marked? Peas are usually affected late after growth is largely completed. 17. The minute black perithecia in groups here and there in the mycelial weft; not prominent; usually not found on sweet peas. Make DRAWINGS to show the powdery mildew on peas. On lilacs. The powdery mildew on the lilac is so common as to be almost always found on lilacs wherever grown and every year. The leaves are the organs affected. Examine the material provided and OBSERVE :— 18. The character of the mycelial coating. On which surface of the leaf does it develop? 19. The minute black perithecia; their arrangement and distribution on the leaf. 20. Any evidences of pathological effects on the leaves. Make prawincs to show the symptoms of the mildew on lilac leaves. On bittersweet. This mildew is not only common on Celastrus scan- dens L. but affects the foliage of many shrubs and trees. Examine the leaves provided and OBSERVE :— 21. The size and location of the spots; the habit whieh this parti- cular mildew-pathogene has, of sending mycelial branches into the leaf- tissues through the stomata, is responsible for the location of the spot. 22. The chlorotic effect on the leaf-tissue beneath the mildewed area as evidenced through the-upper surface. 23. The character of the superficial mycelial growth. 24. The comparatively large and numerous perithecia in all stages of development, the younger ones smaller and brown or yellow in color. DRAW to show a leaf with a mildewed spot. ETIOLOGY Powdery mildew pathogenes all belong to the Erysiphaceae, a family of ascomycetous fungi. They are characterized among other things by their habit of growing externally over the surface of their hosts. They attach themselves by means of short haustoria sent into the epidermal cells. One or two species are known to send intercellular hyphae through the stomata into the tissues. The diseases above studied and their respective pathogenes are:—the powdery mildew, of rose, caused by Sphaerotheca pannosa (Wallroth) Léveillé; of phlox, caused by Erysiphe Cichoracearum DeCandolle; ing of peas, caused by Erysiphe Polygont DeCandolle; of lilac, caused by Microsphaera Alni (Wallroth) Winter; of bittersweet, caused by Phyllactinia Corylea Karsten. Besides the genera above represented, two more, Uncinula and Podosphaera are known, species of which occur on trees or shrubs of the yard and garden. Examples:—Podosphaera Oxyacanthae (DeCandolle) de Bary, on species of Crataegus, Prunus, Spirea and others; Uncinula Salicts (DeCandolle) Winter, on species of Salix and Populus. Life-history. The powdery mildew fungi exhibit such similarity in structure and life-habits that the same outline will serve for the study of the life-history of any of them. From_.this point the student will follow the outline as given for the Powdery Mildews of Trees and Fruits, p. 125, including the subject designated for the report. POWDERY MILDEW OF CEREALS AND GRASSES This 1s a very common and sometimes serious disease of wheat, rye and other cereals. It is also to be found commonly on various wild grasses, especially species of the genus Poa. SYMPTOMS The powdery mildews are detected chiefly by the pathogene-structures developed upon the exterior of the host. There are also some accompany- ing affects or symptoms exhibited by the host. The lesions are confined largely to the leaves and leaf-sheaths. In the material provided, OBSERVE —- 1. The densely matted white, sometimes brownish, mycelial patches on the surface of the leaf (upper and lower). In the fresh condi- tion these patches are powdery due to the abundance of conidia, hence the name, powdery mildew. 2. On the wheat leaves especially, the minute black bodies buried in the mycelial mass, usually most abundant at the center of the spot. These are the perithecia of the pathogene. 3. The effect on the tissues of the leaf beneath and about the mycelial mat. Note that in some cases the entire leaf has turned brown and died. Make SKETCHES showing these symptoms. Where the attack is severe, there is a dwarfing of the heads or a shriveling of the maturing grains, or both. If material is available, study and com- pare with healthy heads and grains. Make skeTcHEs to show the compari- son. Examine the illustration specimens of powdery mildews on various hosts provided and NoTE:— 4. The marked similarity in the symptoms exhibited by all of them. Select one of the specimens and sketcH. Label fully. ETIOLOGY The powdery mildew of cereals and grasses is caused by Eryszphe graminis DeCandolle, the conidial form of which is known as Oidium monilioides Link. Like all the other powdery mildew pathogenes it is an ascomycetous fungus belonging to the family, Erysiphaceae. They all develop externally upon the surface of their host except for short haustoria sent into the epidermal cells or, in the case of one or two species, an occasional mycelial thread sent through stomata into the tissues. Life-history. This pathogene exhibits during its life-cycles all of the characteristic structures of the powdery mildew fungi. The Primary Cycles are initiated in the spring. The sources of inoculum are the overwintered perithecia on the leaves and stubble of the host. Pathogenesis. Remove some of the minute black perithecia from the mycelial mats on the old overwintered host-leaves. Crush in a drop of water by pressing on the cover-glass. OBSERVE :7— 5. The large ellipsoidal ascospores forced from the perithecia; some still in the asci. Determine the number of asci in each peri- 120 121 thecitum. These constitute the primary inoculum. DRAw to show the form and structure of these ascospores. When the ascospores are mature and the perithecium is thoroughly wetted, it cracks open and the ascospores are forcibly discharged. Borne by the wind, they fall upon the growing leaves of the host and germinate. If viable ascospores are available, study spore-germination as seen in the slides provided. DRAw, or copy illustrations provided by the instructor. As soon as this germtube has developed a food-relation with the host by means of haustoria in the epidermal cells, a mycelium begins to develop, branching and spreading in all directions over the leaf-surface. Examine, under the binocula rmicroscope, one of the white mycelial mats on the diseased green leaves (fresh or preserved) provided and OBSERVE :— 6. The tangle of silver-white hyphae with long spreading branches about the margin of the lesion. 7. The numerous erect chains of conidia borne on short conidio- phores. Many of these conidia have fallen off and give the mealy appear- ance to the mildew-spots. Scrape the mycelial mass from the surface of the leaf. Mount in water, cover and EXAMINE :— 8. Conidia; large ellipsoidal, flattened slightly at the ends; their thin hyaline walls and densely granular protoplasm. 9. Conidiophores; short, with a swollen base just above the point of attachment to the mycelium. Try to find a conidiophore with several conidia still attached. 10. The mycelium; very crooked and much broken in scraping from the leaf; septate or nonseptate? As the mycelium spreads over the surface of the leaf it sends minute branches through the outer cell-wall of the epidermal cells. This branch enlarges and branches within the cell to form the finger-like haustoria. Study these in the slides provided or from the drawings by Smith, Bot. Ga7029." pl Xd and XT: Make a composite DRAWING to show a cross-section of the epidermal cells of the host with haustoria, mycelium, conidiophores and conidia in normal relation to each other. These conidia break off at the top of the chain as fast as matured and, scattered by the wind, initiate secondary cycles. Conidia continue to be produced for a time by the mycelium on the primary lesions. As the primary lesions are largely on the young or seedling-leaves of the host, the mycelium probably perishes along with the young leaf before the sexual fruit-bodies can be developed. These appear later on the mycelium of the secondary cycles. There is, therefore, no saprogenic phase in the primary cycles. The Secondary Cycles are initiated by conidia from the primary cycles. Pathogenesis. Thefungusexhibits the same conidial structures in the secondary cycles as those just studied. As the host-tissues begin to mature, conidial production ceases, and the mycelium begins the development of sexual structures. The detailed study of the development of these struc- tures cannot well be followed out in this laboratory exercise. (See de Bary, Morphology and Biology of the Fungi, p. 226, fig. 107.) The structure of the perithecium may, however, be readily studied. Examine the specimens provided under the binocular microscope. OB- SERVE — 122 11. The much coarser and more densely matted mycelium; not pure white but yellowish or brownish. 12. The globose perithecia of varying sizes and colors enmeshed in the mycelial mat. SKETCH to show the appearance under the binocular microscope. Saprogenesis. The perithecia usually begin to appear while the leaf is still green, but do not mature their ascospores until the leaves die and are overwintered. The perithecia on the dead leaves on the ground pass the winter in an inactive condition. The rains and warm weather of spring cause the asci to mature their ascospores. To simulate the spring conditions, some of the leaves bearing immature perithecia have been placed in warm water for several days. They are now mature. Remove some of the perithecia to a slide in water and cover with a cover- glass. Crush by pressing firmly on the cover with the handle of a scalpel, while watching the perithecia under low-power. What comes out of the perithecium? How many? What is the character of their contents? Does the perithecium have an ostiolum? DRAW to show a perithecium with its contents. Show the structure of the perithecial wall and mycelial attachment. With the maturity and discharge of the ascospores, the secondary cvcles are completed. REPORT 1. Explain the significance of biclogic strains in E. graminis DC., with respect to control. 2. Discuss eradication measures in the control of powdery mildews. POWDERY MILDEWS OF TREES AND FRUITS Powdery mildew diseases have been reported on about 1500 species of wild and cultivated plants. Several of them are frequently very injurious to fruit-trees and sometimes to shade- and forest-trees. SYMPTOMS Leaves and young shoots are usually the parts of the host that are affected. Throughout the latter part of the summer the powdery mil- dews are conspicuous and give to the infected parts of the host-plant a whitish, mealy or dusty appearance, due partly to the superficial white web-like mycelium of the pathogene, and partly to the presence of myriads of rapidly formed white conidia. Later in the summer, and in the autumn, there usually appears, on the affected parts, the small black spherical perithecia of the sexual stage. In the autumn these are more in evidence than the whitish growth; the latter often disappears. These signs, the fruit-bodies of the pathogene, are usually the most striking evidences of the disease. Definite and characteristic symptoms resulting from the effects of the pathogene on the host are, however, not wanting in many cases. On the cherry. On this host, the leaves and twigs show the effects of the disease. Examine the specimens and photographs provided and OBSERVE :— 1. The upward rolling or curling of the leaf-blades parallel with the mid-rib. 2. The shorter and thicker internodes of diseased twigs as com- pared with healthy ones. 3. The weft-like coating of fine white hyphae on the leaves, especially on the under surface. The mycelium of most of the powdery mildew pathogenes is entirely superficial. 4, Patches of the mycelial weft dotted with the minute black perithecia of the pathogene. Make a DRAWING of a diseased twig to show the signs and symptoms exhibited. On the apple. The young leaves, flower clusters and shoots are af- fected. Examine the diseased shoots and U. S. Agr. Dept. Bul. 120, pl. I and VI, provided. oBSERVE:— 5. The marked hypoplastic effect exhibited in the dwarfed foliage. 6. The mealy white coating of the diseased leaves,—conidia and mycelium of the fungus. 7. The thick felty mycelial coating on the watersprouts collected in the autumn. Note the dirty white or brownish tinge as compared with the pure white of the growth on the leaves. 8. The minute perithecia, more or less embedded in the mycelial mat on the shoots. Make pRAwINGs to show the appearance of affected leaves and water- sprouts. On the peach. Not only the leaves and twigs, but also the fruits of the peach, are subject to the disease. Study the specimens and photo- graphs provided. OBSERVE :— 123 124 9. That the leaves are narrow, have failed to expand and are curled and deformed. Chlorophyl is not developed properly and the leaves show red and yellow tints. Defoliation often results from a severe infec- tion. 10. The effect on the more succulent upper parts of the twigs. 11. The felty character of the superficial mycelium which forms in white patches over affected leaves and twigs. This thick mycelial felt persists on the twigs after the leaves fall, becoming a dirty gray-brown in color. 12. The more or less circular white patches of mycelium on the fruit. When very young fruits are affected they soon fall. Perithecial fruit-bodies rarely appear. Make pRawincs to show the symptoms exhibited by the powdery mildew of the peach. On the grape. This disease is more destructive and develops more typically in the Pacific Coast regions than in eastern United States. All herbaceous parts of the host are affected. Examine the specimens pro- vided. OBSERVE :— 13. The whitish patches on the upper and lower surfaces of the leaf. How do they compare with the spots of the downy mildew? These spots may spread to form a whitish, mealy coating over the greater part of the leaf-surface. Badly diseased leaves may curl upwards about the edges. 14. The small black perithecia scattered over affected areas on the leaves. 15. The diseased canes. They also show the superficial greyish white patches of mycelium beneath which the tissues of the cane soon darken, making it spotted. (See California Bul. 186, fig. 3.) 16. The diseased berries. (See California Bul. 186, fig. 4.) Blossoms and young fruits when affected, quickly fall. The disease may often cause shelling of the large green berries when the fruit-pedicles are affected. Make prawincs from specimens and illustrations to show the symptoms of the powdery mildew of grapes. On the gooseberry. In case of the gooseberry mildew, it is chiefly the young shoots and the fruits that are affected. In the material provided, OBSERVE :-— 17. The mycelial mats coating the shoots; color, thickness and distribution. 18. That the superficial mycelium spreads out over the leaves. How is the growth of leaf and stem affected? 19. The character of the mycelial patches on the fruits. Does the growth and development of the fruit appear to be affected? 20. The black perithecia of the pathogene embedded in the mycelial felt. This same gooseberry mildew may sometimes seriously affect some varieties of currants, as may be seen in the specimens provided. Make prawincs of mildewed shoots and fruits of gooseberry or currant. On the chestnut. The leaves are the organs affected. This powdery mildew affects not only chestnut but a great variety of trees, shrubs and woody vines. Examine the diseased leaves provided. OBSERVE:— 125 21. That the mildew-patches are confined to the under surface of the leaf. 22. The rather thick He character of the mycelial growth; color and extent. 23. The numerous perithecia sitting on the mycelial mat, not embedded in it; larger than the perithecia of the other mildew- pathogenes observed; some of them immature as indicated by their small size and light color. 24. Any evidence of injury showing on the upper surface op- posite the mildew-spot. DRAW a leaf showing the characters of the mildewed areas. On the willow. Many species of willow and also poplars are affected. The leaves are usually the only organs involved. In the specimens provided, OBSERVE :— 25. The location and distribution of the spots; hypophyllous or epiphyllous? 26. The characteristic dense white mycelial border of the spot with darker center, especially in older lesions, due to the numerous black perithecia. Willows are often defoliated by this disease. 27. Any evidence of injury to the tissues. DRAW a willow leaf showing the mildew-spots. ETIOLOGY The powdery mildew diseases are all caused by species of ascomycetous fungi belonging to a single family, the Erysiphaceae. Each disease above studied is caused by a different species of pathogene. Even within some of these species there are doubtless biologic species. The diseases studied with their respective pathogenes are as follows:—-the powdery mildew, of cherry, caused by Podosphaera Oxycanthae (DeCandolle) de Bary; of apple, caused by Podosphaera leucotricha (Ellis and Everhart) Salmon; of peach, caused by Sphaerotheca pannosa (Wallroth) Léveillé, var. Persicae Woronichin; of grape, caused by Uncinula necator (Schweinitz) Burrill; of gooseberry and currant, caused by Sphaerotheca Mors-uvae (Schwei- nitz) Berkley and Curtis; of chestnut, caused by Phyllactinia Corylea Karsten; of willow, caused by Uncitnula Salicts (DeCandolle) Winter. Besides the four genera represented, Podosphaera, Sphaerotheca, Uncinula and Phyllactinia, two more are known, species of which are very common in this country. Examples:—Erysiphe graminis DeCandolle, on grasses and cereals and Microsphaera Alni (Wallroth) Winter, on lilac. (See demonstration specimens.) Life-history. These powdery mildew pathogenes all exhibit such similarity in their structures and life-habits that the following outline should serve for the study of any of them. As they are strictly obligate parasites, saprogenesis is a period of rest or a maturation-process carried on at the expense of stored food-reserves. The Primary Cycles are initiated in the spring or early summer. The primary inoculum is usually the ascospores from overwintered peri- thecia. In some cases, as in that of S. pannosa (Wallr.) Lév., or of Podo- 126 sphaera leucotricha (E. and E.) Salm., the mycelium may winter in a semi- dormant condition within the host-buds on the embryonic leaves. As these buds open and the leaves and shoots develop in the spring, the myce- lium grows out over them and produces conidia, which, scattered to healthy shoots, may initiate primary infections. (See U. S. Agr. Dept. Bul. 120:9-10.) Ascospores are, however, responsible for the primary infections in the case of most powdery mildews and often even in those in which hiber- nating mycelium is known. Pathogenesis. Kemove with the scalpel, several perithecia of one of the pathogenes indicated by the instructor. Mount in a drop of potas- sium hydroxide. Cover and, while examining it under the low-power, crush the perithecium by gently pressing on the cover-glass with the point of the scalpel. ORSERVE:— 25. The irregular crack in the perithecium from which one or more asci are forced out. How many in this case? 26. The large ellipsoidal ascospores usually remaining within the asci; number in each ascus; color; contents. 27. The thin place in the wall of the ascus at the apex. At maturity this dissolves as the perithecium cracks open and the ascospores are forcibly ejected into the air. Make a diagrammatic DRAWING of a cracked perithecium with protrud- ing asci discharging spores. Borne by the breeze, these ascospores fall upon young shoots or leaves of the host and germinate. The germtube grows out over the surface and sends a haustorium into the epidermal cells, from which point the branching mycelium develops. Study germinating ascospores or illustra- tions provided, especially Bot. Gaz. 29, pl. XI-XII. Make a diagram- matic DRAWING of a germinating ascospore with haustorium. To study the mycelium, scrape some from the surface of young spots; tease apart in water or potassium hydroxide; cover and examine. OB- SERVE :— 28. The broken pieces of irregular, branched mycelium; septa, color and contents. 29. The large, ellipsodial or ovoid conidia; color and contents. Several may be found attached in a chain or even still on the conidiophore. 30. The short conidiophores,—upright branches which bear the conidia ina chain. (See the demonstration specimen under the binocular microscope; or U.S. Agr. Dept. Bul. 120, fig. 2.) Make a diagrammatic DRAWING to show the vegetative structures in position on the leaf-surface. The conidia are produced in great quantities. They give the powdery appearance so characteristic of these mildews. They are scattered by the wind and initiate secondary cycles. After a period of conidial production, the mycelium begins to form the sexual fruit-bodies,—the perithecia. These usually begin to develop toward the end of the growing-season but before the leaves fall. In some cases as in the apple mildew-pathogene, P. leucotricha, the perithecia are formed on the twigs. The detailed study of the development of the sexual bodies and the formation of the perithecium cannot well be under- taken in this exercise. (See de Bary, Morphology and Biology of the Fungi. p. 226, fig. 107.) 127 Saprogenesis. The perithecia do not complete their development until the late autumn, usually after the leaves fall. Some do not mature until the following spring. They develop and mature at the expense of food gathered by the parasitic mycelium. Select from the material provided, representatives of two or more genera. Study the perithecia. OBSERVE :— 31. The shape, color and structure of the perithecium; the nature of the appendages. DRAW one perithectum with its appendages. Study species from the three remaining genera, OUTLINE the perithecia, but DRAW carefully a typical appendage for each. (See Salmon, Mono- graph of the Erysiphaceae, pl. 1-7; also Burrill, Parasitic Fungi of Illinois, p. 395-397.) Crush the perithecium in each case and examine. In this connection the following key :—- A. Perithecia with one ascus. 1. Appendages simple, undivided at tip........... SPHAEROTHECA 2. Appendages once or more dichotomously divided at the tip...... a0 tiie ede HARE SepeMS Cy Amen eh s eters 6a MPODOSPHAB RA B. Perithecia with several asci. 1. Appendages never more than slightly swollen at the base. a. Appendages simple, or irregularly branched: without tip OPCML TTA CRE SRE NI ONL AIG Aaa at Mae ERYSIPHE b. Appendages once or more dichotomously branched at the iERO) Mh Ae oa ee Ral ee ae Te EL eR MICROSPHAERA @ .vppendages spirally rolled ‘at. the tip... ...2...2.: UNCINULA 2. Appendages swollen at the base so as to form an enlarged plate. . . Sed head ke eg A ON Us VT ly SO oe HO ten San CA PHYLLACTINIA With ascospore-discharge in the spring and early summer, saprogenesis of the primary cycle ends. The Secondary Cycles are, as pointed out above, initiated by the conidia from the primary lesions. They normally repeat in all details the phenomena and structures exhibited in primary cycles. Secondary cycles may repeatedly initiate other secondary cycles during the season. REPORT 1. Discuss control of one of the powdery mildews which may be selected, treating the subject under the headings of eradication and protection and explain how the life-habits of the pathogene make effective the measures described. APPLE SCAB Of all the diseases of the apple, this is the most common and best known to the growers. It is the one fungous disease for which they spray. It is world wide, occurring practically wherever the apple is grown. While there is a marked difference in the susceptibility of varieties, all will suffer some under conditions especially favorable to the fungus causing the disease. ‘The scab of the pear is very similar in its symptoms to the apple scab but is caused by a distinct but closely related species of fungus. SYMPTOMS The disease affects the leaves, flowers, fruit and rarely the twigs. Material is provided showing the different symptoms. On the leaves. The first evidence of the disease in the spring is on the unfolding leaves. The scab-spots usually appear first on the lower surface, but later new spots appear on the upper surface. Examine the leaves provided and OBSERVE :— 1. The size, form and character of the spot. The radiating char- acter of the lesion. To what due? 2. The character of the injury to the leaf. Does the injury show on the surface opposite the spot? 3. The difference in the character of the upper and under surface of the leaf itself; and of the scab-spots on the two surfaces of the leaf. 4. The variations in the character of the scab-spots on differ- ent leaves. (Compare Cornell Bul. 335, pl. I.) Make prawincs to show the characters of the scab-spots on the upper and under surfaces of the leaves. On the flowers. The disease may appear on the pedicle and calyx of the flower before the petals fall and may be severe enough to prevent the setting of the fruits. (See Cornell Bul. 335, pl. VII.) In the material provided, OBSERVE :— 5. The location, form and character of thé scab-spots and the effect on the flower. Make DRAWINGS to show these symptoms. On the fruit. Where the infection of the calyx is not severe enough to prevent the fruit from setting, the apple as it grows shows the enlarging scab-spots. These become very evident as the season advances. In the young apples provided, OBSERVE :— 6. The black scab-spots. Their form, size, and effect on the fruit. To what region on the apple are they largely confined? 7. The felty black center of the spot. In some cases, this felt has disappeared and the center of the spot is hard, reddish brown and often cracked. Note the scab-spots on the mature apple provided. 8. The papery rim bordering the spot; best seen in the younger spots. This consists of the cuticle of the apple which has been loosened by the fungus as it spreads out from the center of the spot. (See Cornell Bul. 335, pLaV Lea) Make pRAWINGs to show the points brought out in 6, 7 and 8. Sometimes these spots cause a dwarfing of the apple on the affected side. (See demonstration specimens.) 128 129 On the twigs. This form of the disease appears to be rare except on certain varieties like the Lady apple. In Maine and other very northernly apple sections it is not uncommon on other varieties. In the material provided, OBSERVE :— 9. The rough blistered character of the lesions, confined to the growth of the current year. DRAW. ETIOLOGY The apple scab is caused by the conidial stage, Fusicladium dendriticum (Wallroth) Fuckel, of an ascomycetous fungus known as Venturia inegualis (Cooke) Winter (= V. Pomz (Fries) Winter). It belongs to that group of the ascomycetes known as Pyrenomycetes which have their asci enclosed in a more or less globose fruit-body, called a perithecium. Life-history. It is in the conidial stage that this fungus exhibits its parasitic nature. It lives superficially on the host or nearly so, simply prying off the cuticle or upper part of the epidermal cells, and applying its mycelium closely to the host-tissues. The Primary Cycle is initiated by ascospores from perithecia in old leaves on the ground. Pathogenesis. Crush in potassium hydroxide a bit of the old leaf provided, examine and OBSERVE :— 10. The 2-celled olivaceous ascospores. DRAW. ‘These ascos- pores are shot from the ascus which protrudes through the ostiolum of the perithecium. Ascospores are discharged only during rains or very moist weather in spring. They are carried to the young leaves just emerging from the buds. Here they germinate. Study Cornell Bul. 335, pl. LX and X, and OBSERVE :— 11. That but one cell of the ascospore gives rise to a germtube. Which cell? praw to show three stages in the development of the germ- tube. This germtube pierces the cuticle of the leaf or young fruit and initi- ates the scab-spot. copy Cornell Bul. 335, fig. 185. Again examine the scab-spots on the leaf and with the hand-lens or low-power, MAKE OUT :— 12. The radiating branched mycelial threads. Why do they radiate from a center? Make an enlarged DRAWING of a scab-spot to show this habit of the mycelium. Study the mycelium, as shown in the prepared slides of apple leaves which have been cooked in potassium hydroxide and the epidermis, bearing the fungus, peeled off. OBSERVE:— 13. The form, size and septation of the mycelium. Its color and method of branching. No haustoria are sent into the host-cells and the mycelium does not at this stage penetrate beyond the epidermal cells. 14. That the conidiophoes arise in clusters or singly from this spreading mycelium. Note their form, length and color. 15. The conidia lying about, which have been broken off from the conidiophores; their form, size and colorand point where they were attached to the conidiophore. Several conidia may be produced from near the same point on a conidiophore. How? See if you can find a conidiophore which shows this. Make pRAWINGs to show the mycelium, conidiophores and conidia in their proper relations to each other and to the host. 130 Scrape some of the conidia from the scab-spot on an apple. Mount and study. Compare them with those found in the prepared slide. They are sometimes 1-septate. Make pRAwInGs to show the variations in size, form and septation of the conidia. Saprogenesis. The mycelium in the primary lesions on the leaves continues to produce conidia until the leaves fall. The fungus, which has up to that time lived practically on the surface, now sends new branches of the mycelium throughout the dead tissues of the leaf. From this mycelium are formed the globose perithecia. They are formed just beneath the epidermis of the lower or upper surface of the leaf, being most abundant near the surface facing upward as the leaf lies on the ground. Examine the old apple leaves provided and OBSERVE :— 16. The evidence of the old scab-spots of the summer. 17. With the hand-lens the pimple-like perithecia scattered over both surfaces of the leaf just beneath the epidermis. Note the color, size, distribution, relation to the old scab-spots, and relative abundance on two sides of the leaf. Make a DRAWING of a portion of the leaf to show the perithecia as seen with the hand-lens. With the scalpel, cut from the leaf a small square of tissue showing an abundance of the perithecia. Place between pieces of pith and with a razor make freehand sections through the perithecia. Mount and study. OBSERVE :— _ 18. The shrunken dead condition of the host-tissue. 19. The imbedded perithecia. 20. The mycelium of the parasite throughout the tissues of the leaf; its form and character. 21. The structure of the perithecium. (Best made out in the stained sections.) The walls, their relation to the host-tissues, form, size, mouth or ostiolium and asci, with ascospores. How many ascospores in an ascus? Make a DRAWING to show the structure and contents of the perithe- cium and its relation to the host-tissues. The perithecia begin to develop in the autumn but do not mature their ascospores until spring at the time when the apple leaves and blossoms are unfolding. Secondary Cycles are initiated by the conidia from the lesions on leaves and fruits on the tree. Aside from their conidial origin, the secondary cycles which are continuously initiated throughout the season, do not differ from the primary. 22. Study the germinating conidia. DRAW. The fungus forms on the fruit a thick stroma-like growth from the upper surface of which arise the short conidiophores bearing the conidia. In order to study this structure and the relation of the parasite to the tissue of the fruit, make thin cross-sections through the scab-spots on the half- grown fruits. OBSERVE :— 23. The thick stroma-like mass of the mycelium. Note its pseudoparenchymatous structure; thickest toward the center of the spot. 24. The short conidiophores with conidia. Find conidiophores that show different stages in their formation and development. 131. Make a DRAWING to show the structures observed. Pathological Histology. Study the prepared sections made through a scab-spot on the fruit. OBSERVE:— 25. That the fungus works in the cuticle above the epidermal cells, splitting off and forming the papery rim of cuticle that covers the advancing margin of the fungous growth. This is best made out at the very edge of the lesion. 26. The suberization of the cells of the host just under the fungous stroma, indicated by the browning of the cell-walls. Why does this occur? REPORT 1. Give a concise account of the life history of Venturia in- @qualis (Cke.) Wint. Arrange your data under and show the heads and subheads used in this outline. ERGOT OF RYE This disease is one of the earliest known and most frequently studied of ascomycetous diseases of cereals; due doubtless to the poisonous effects of the sclerotia of the pathogene on man and beast, rather than to the reduction of crop-yields which it causes. The host of greatest economic importance is rye. SYMPTOMS The heads alone show the disease which is exhibited chiefly by the presence of the pathogene structures. In the early stages, the pathogene produces a honeydew which exudes and runs down over the young spikelets. Examine the dried specimens labeled ‘‘ honeydew-stage,”’ and photograph 1, fig. 2, 4 and 22, and photograph 9. OBSERVE:— he Smudgy traces of the now dried honeydew. This honeydew is often difficult to see in dried specimens but in fresh specimens it is often very copious and sticky. Carefully dissect away the glumes in the smudgy region. OBSERVE:— 2. The whitish kernels with corrugated surfaces. Compare with normal kernels from the same or healthy heads of the same age, as to size and color. 3. The glumes about the diseased kernels. - Are they diseased? Compare with healthy. It is from these diseased kernels that the honeydew oozes, but in the dried specimens, there is evident only the whitish covering of the dark diseased kernels. Make a pRAWING of the organs of a single diseased and healthy spikelet to bring out these characters. Later there is developed the ergot stage. Examine the specimens and photographs provided and OBSERVE :— 4. The black spur-like hodies projecting here and there from between the glumes,—the ergots; average number from each head. Exam- ine illustration specimens of other ergot-infested grasses. DRAW a head of rye and a head of one other grass showing the ergots. Examine the loose ergots provided. NOTE:— 5. The variation in size and shape; consistency; the surface, often checked and cracked. These ergots are sclerotia of the pathogene developed, in place of the host-kernel, from the structures of the Sphacelia stage, the shrunken remnant of which may often be observed still clinging to the tip of the sclerotium. 6. On breaking one open, the light colored interior. These ergots are poisonous. Make an enlarged detailed DRAWING of two or more of the ergots. ETIOLOGY The ergot is produced by the ascomycetous fungus, Claviceps purpurea (Fries) Tulasne, the conidial or honeydew-stage of which was given the name, Sphacelia segetum Léveillé. Life-history. Several careful researches have resulted in a rather complete knowledge of the life-history of this pathogene. Primary and secondary cycles with sharply marked pathogenesis and saprogenesis occur. 132 133 The Primary Cycles are initiated in early summer at the time the rye or other grass-hosts begin to head-out. Pathogenesis. Ascospores which are produced in the spring constitute the inoculum for the primary cycles. From the ergots (sclerotia), which overwinter on the ground, there develop in the spring, stalked fruit-bodies. In the heads of these are developed numerous perithecia containing the asci with long slender ascospores. Examine the specimens provided or photograph 4, fig. 22. OBSERVE:— 7. The little pimple-like dots scattered thickly over the globose head of the fruit-body,—the ostiola or mouths of the perithecia. From these ostiola the long thread-like ascospores are shot into the air and, carried by air-currents, lodge in the infection-courts,—the open blos- soms of the rye or other grasses. A bit of material from a mature stroma will be provided (take clean slide to materials room). Crush, cover and study. OBSERVE:— 8. The long slender ascospores; some floating free, others still in the asci; continuous or septate? DRAw several ascospores. (Keep this slide for No. 20.) These germinate within the blossom. Examine photograph or de Bary, Morphology and Biology of the Fungi, p. 227, for germinating ascospores. NOTE :— 9. That upon germination the spore at once becomes, to all intents, a part of the mycelium. copy. The branching germtubes quickly penetrate the young ovary and, grow- ing throughout its tissues, develop the Sphacelia or conidial form of the fungus. Study cross-sections (freehand or prepared) of the upper end of the ovary (made during the Sphacelia stage). Examine with the high-power. OBSERVE :— 10. The numerous irregular cavities lined with erect conidio- phores. Note the irregular dark masses of host-cells. DRAW a small portion of the hymenium with underlying host-tissue, showing the conidia and the manner in which they are borne. The honeydew consists of a sweet fluid, exuded by the pathogene, in which great numbers of these conidia find their way to the surface of the spikelet. Insects attracted by the honeydew serve as inoculating agents in starting the secondary cycles. Very soon after, the conidia mature and the mycelium in the basal portion of the ovary begins to develop the sclerotium, which, as it grows and develops, replaces the host-cells and pushes forth as a long black spur with the shriveled Sphacelia structures at its tip. It is at first light colored, inclined to purplish but soon turns black. (See illustration specimen. ) Examine photographs 3, fig. 25 and 4, fig. 13-14. NorE:— 11. That while the sclerotium usually replaces the entire ovary, this is not always the case. copy from the above figures to show this. Make very thin cross-sections of one of the mature sclerotia and study under the high-power. OBSERVE :— 12. The pseudoparenchymatous structures. 13. The thick walls and small lumina of the hyphae composing the sclerotium. Are there any evidences of host-tissue? 154 14. The dark color of the outer coat or rind; number of cells thick; the white color of the medulla. Detail in a DRAWING the structure of the sclerotium. Saprogenesis. ‘These sclerotia, when mature, fall to the ground or find their way at threshing into bins along with the rye grains. With these they may be sown and find their way to the soil. Here they remain dormant until spring, when the fungus again becomes active. At any point beneath the rind, growth-centers may be set up from which are developed slender stalks with globose tops. These are developed at the expense of the food-materials stored in the cell-walls of the sclerotial medulla. Examine the so-called germinating sclerotia provided, OBSERVE :— 15. The small, capitate bodies arising from the sclerotium,— the stromata. Note the comparative size of the stem and the head. Examine the stromata carefully with a hand-lens, noting the small dots or punctations. - Make a DRAWING to bring out all the external characters of the stromata and how they arise from the sclerotium. Prepared slides of cross-sections of the stromata are furnished. Examine with the low- and high-powers and OBSERVE :— 16. The ovate acuminate cavities,—perithecia. Note the dense pseudoparenchymatous wall. 17. The location of the perithecia about the periphery. : 18. The opening at the top,—ostiolum. Note that it pro- trudes. Make an outline DRAWING of the cross-section of the entire stroma. 19. The asci arising from the bottom of the perithecium. 20. Within the asci, the bundle of eight thread-like spores. Supplement at this point with the crushed mount prepared under number 8. Stain by running a little methyl blue under the cover-glass. Make an enlarged DRAWING of a perithecium containing the asci; and of a single enlarged ascus with the ascospores. Secondary Cycles initiated by the conidia of the Sphacelia stage, multiply and spread the pathogene during the blossoming-period of the host. The Sphacelia stage, followed by the development of the ergot, is produced as in the primary cycles. REPORT 1. Make one or more cartoon-like sketches to illustrate the life- history of Claviceps purpurea (Fr.) Tul. ONION SMUT This disease is most prevalent in the northeastern part of the United States where in certain localities 1t causes a considerable loss. Because of its striking symptoms it has been known to onion-growers for many years and has been the subiect of study by scientists for at least the past forty years. SYMPTOMS Examine a diseased seedling. OBSERVE :— 1. The narrow, yellow lesions extending parallel with the leaves. These are the first symptoms to appear. 2. The narrow, black areas which are most numerous near the base of the onion and sometimes extend almost to the tip of the leaf. The yellow areas will later become darkened like these. 3. That these black masses are all enclosed within the tissue of the leaf, or that occasionally the epidermis is ruptured. 4. That in cases where the leaf is badly affected, its tip has withered and droops. Make a DRAWING of a diseased seedling. Examine one of the larger diseased onions. OBSERVE :— 5. That in this case each badly diseased leaf has turned brown and has fallen over. 6. That the black lesions have now broken open, forming long black open sori from which a sooty-like mass is sifting. DRAW. ETIOLOGY The pathogene reponsible for this disease is Urocystis Cepulae Frost, a basidiomycetous fungus of the order Ustilaginales. There are two families in this order, the Ustilaginaceae and Tilletiaceae. To the former belong those organisms which produce the loose smuts of wheat, oats and corn, while to the latter belong the pathogenes like those producing the stinking smut of wheat, and the onion smut. Life-history. The Primary Cycle has its origin in the chlamydospores found in the infested soil. Pathogenesis. These spores, when near germinating onion seeds, also germinate sending out a long branched mycelial thread. This my- celium probably enters the host directly, or it may possibly produce conidia or sporidia borne on the tips of the mycelial branches. In the latter case it is the germtuhbe which grows from the sporidium, that enters the tissue of the host. Infection always takes place under ground and only when the seedling is just emerging from the soil. No new infections occur after the onion becomes older. This mycelium develops within the leaf-tissues, giving rise to the long black sori. Scrape a few spore-balls from a sorus and, under the microscope, OBSERVE :— 7. The size, color and surface markings of the spore-ball. It is made up of a central thick-walled resting-spore (one or more celled) surrounded completely by thin-walled pseudospores. Only the central cells are viable. If the inner structure can not be determined from the mount, consult Duggar, Fungous Diseases of Plants, p. 382. 135 136 Make a diagrammatic DRAWING showing the structure of the spore-ball. If no germinating spores are available, sketch the illustration shown in the above reference. Cut a cross-section of an onion seedling through a closed lesion or use prepared slides. OBSERVE :— &. The depth to which the sorus penetrates. 9. The black mass of spores lining the sorus. Are they attached to stalks? How are the spores of a smut-pathogene usually borne? (See McAlpine, Smuts of Australia, p. 19.) 10. The cuticle still intact and retaining the spores which later escape. 11. The mycelium penetrating the tissues adjoining the sorus. Do any of these cells appear dead? Make a DRAWING of a cross-section of a sorus with the host-tissue surrounding it. Saprogenesis. There is no vegetative activity during saprogenesis. The spores lie dorrhant in the soil or host-debris. They have been known to live over in the soil as long as twelve years. Secondary cycle. Unlike most fungi this pathogene has no secondary cycle. Infection takes place only during a limited period while the host is in the seedling stage. They are initiated only by overwintered spores. Consequently, even if onion sets are transplanted to badly infested soil, the onions will remain free from the disease. REPORT 1. Discuss the use of sulphur and of formaldehyde in the control of this disease, including the advantages or disadvantages in methods of application, the amounts used, cost, and the preference of the onion- grower of the present day. LOOSE SMUT OF WHEAT This disease is exceedingly common and often destructive in the wheat- fields of eastern United States and Canada. It is readily distinguished from the stinking smut. The latter, while not uncommon in the east, is much more general and destructive than loose smut in the great wheat- lands of the west. While the loose smuts of wheat and oats are much alike in general appearance, they differ strikingly in certain features of the life- history of the respective pathogenes. SYMPTOMS The evidences of the disease are to be observed chiefly in the heads at blossoming-time. Compare the diseased and healthy heads provided. NOTE :-— 1. The general effect of the disease on the form and appearance of the head. Does it affect the rachis as to length and size; length of internodes? pRAw both diseased and healthy heads. 2. The effect on the individual spikelets. Determine this by carefully dissecting out the parts of the (moistened) healthy spikelets and flowers. pDRAw. Dissect and prAw the parts of the diseased spikelet. 3. That the culms of a diseased plant at first grow more rapidly and outstrip those of the healthy plant. Eventually, after spore dispersal, the healthy culms push up above the diseased ones. (See whether later studies will explain this.) 4. The naked rachides from which the spore-masses have disappeared. DRAW. ETIOLOGY The loose smut of wheat is caused by the basidiomycetous parasite, Ustilago Tritict (Persoon) Jensen. It isa member of the order of primitive basidiomycetes, the Ustilaginales commonly known as the smut-fungi. ‘There are two families in this order, the Ustilaginaceae to which U. Tritict belongs and the Tilletiaceae to which belongs the stinking smut-pathogenes, Tilletia Tritict (Bjerk.) Wint. and Tilletia foetens (B. and C.) Trel. Life-history. While the parasite causing this disease has long been known, it is but recently that its life-history has been completely under- stood. (See Pl. Ind. Bur. Bul. 152:10-12.) It differs, along with U. nuda (Jens.) Kell. and Sw. in barley, from most of the other smut-fungi whose life-history is known, in that infection occurs through the stigmatic sur- faces of the pistil at flowering-time. There are no secondary cycles. The Primary Cycle requires a full year for its completion. There is no saprogenesis, the pathogene remaining in continuous association with the living host except for the few minutes during transfer from the source of inoculum to the infection-court. Pathogenesis. The black smutted heads emerging from the upper leaf-sheaths at flowering-time constitute the sources of inoculum. Mount some of the sooty mass in a drop of potassium hydroxide, cover and examine with the high-power. OBSERVE :— 5. The numerous brown globose bodies scattered through the mount,—the chlamydospores. These, in the case of this smut-fungus, constitute the inoculum. 137 138 6. Their color (lighter on one side); markings; variations in form. (See demonstration microscope.) DRAW five different spores. While the chlamydospores of most smut-fungi are resting-spores, those of U. Tritict, on account of the blossom-infecting habit of the patho- gene, have largely lost their ability to remain viable for a long period. The dusty dry chlamydospores are scattered by the wind over the blossoming wheat. Some spores fall upon the exposed stigmas protruding from the open glumes of healthy heads. Here they germinate, sending a long germtube along and into the stigmatic filaments and by way of them into the young ovary. If germinating spores are available, study and. OBSERVE :—- 7. The long germtubes, septate and with knee-joint fusions. 8. The uniform absence of sporidia. DRAW several germinating chlamydospores to show variation. This germtube is morphologically a basidium which in most other species of Ustilago produces basidiospores or sporidia as they are called. In this species, sporidial production is unnecessary. After penetrating to the ovary, the germtube branches and, establishing itself near the grow- ing-point, goes into a dormant condition along with the ripening kernel. The invaded kernel shows no evidence of injury. As the embryonic plant develops upon planting the kernel, the mycelium, aroused by the same condition of heat and moisture (and probably by the activities of the embryo as well), begins active growth, branches and spreads into the stooling culms, and forces its way upward through the tissue as the stem lengthens. When the wheat heads begin to form, the mycelium of the fungus takes possession, completely replacing the more tender or succulent tissues of the spikelet with its dense mats of profusely branch- ing mycelium, thus forming the black, easily ruptured sori of the smut. The diseased heads emerge from the sheath about the time the flowers on the healthy heads are in full bloom. Why? REPORT 1. A farmer writes for information on the nature and control of the loose smut of wheat. Write him a letter giving clearly and concisely the information he needs. LOOSE SMUT OF OATS There are two smuts of oats, the loose and the covered. . Loose smut is much the more common and the one usually referred to as oat smut. This disease occurs wherever oats are grown and may often destroy from 25 to 50 percent of the crop. Its control is exceedingly simple and effective. SYMPTOMS The evidences of loose smut are usually confined to the inflorescence, though the leaves may rarely show lesions. Compare the specimens of this disease with healthy specimens provided. OBSERVE :— 1. The striking difference in the panicles of the two; form, size and color. DRAW. 2. In the entire plants (illustration specimens) the relative length of straw, number of stalks in the stool, amount and character of leafage. 3. The differences in the spikelets of each; empty glumes, hull and flower parts (most easily determined by dissecting specimens in water). Make enlarged DRAWINGS to show comparatively the effects of the dis- ease on the parts of the spikelet. Compare specimens of loose smut with those of covered smut. SKETCH to show differences. ETIOLOGY The pathogene causing the loose smut of oats is Ustilago Avenae (Persoon) Jensen. It is closely related to Ustilago Tritict (Pers.) Jens. but differs strikingly in certain features of it slife-history. (See p. 137) The covered smut of oats, caused by Ustilago levis (Kell. and Sw.) Mag., occurs along with U. Avenae from which it is to be distinguished certainly only by its smooth, granular spores. Life-history. There are in the life-history of this pathogene only primary cycles. While not so intimately associated with the living host during the resting-period as is Ustilago Tritici (Pers.) Jens., it normally exhibits little saprogenic activity under natural conditions. The Primary Cycles are initiated at blossoming-time, at which time inoculation occurs. Pathogenesis. The smutted plants scattered through the field are the sources of inoculum. Remove a bit of the black mass from a smutted head to a drop of potassium hydroxide on a slide; cover and examine. OBSERVE :— 4. The numerous brown, globose bodies scattered through the mount,—the chlamydospores. 5. Their color (lighter on one side); markings and variations in size. DRAW three different spores. (See demonstration microscope, oil-immersion.) These chlamydospores are resting-spores and may retain their vitality for several years. The chlamydospores, disseminated when the oats are in blossom, lodge within the oat hull next to the kernel. They do not germinate at once as do those of U. Tritici but lie dormant as the oat hull closes about the maturing kernel. The chlamydospores are thus enclosed 139 140 along with the ripe kernel. When the oat grain is planted in the soil and germinates, the same conditions that cause the seed to grow, start the spores into activity. Spores have been germinated on the slides provided. Carefully cover the drop of water containing the germinated spores, and examine. OB- SERVE -— 6. The rather long hyaline germtube or promycelium,—the ~ basidium of this basidiomycete. 7. That it is septate; number of cells into nen it is divided; the crack in the chlamydospore-wall where the promycelium emerges. 8. That from each cell at the septum (above or below?) arises one or more oblong sporidia,—the basidiospores. 9. The variations from the normal germination. Make pRAWINGs to show germination of chlamydospores and formation of sporidia, with such variations as are observed. 10. Examine the mount of germinated spores to see if you can find any of the sporidia germinating. DRAW. As the seedling bursts through the seed-coat and pushes up through the hull, it is penetrated by the germtubes of the sporidia. The mycelium _ of the parasite grows and branches, pushing its way upward between the cells of the host as the culms of the oat come out and shoot upward. Usually every culm in the stool is infested. The mycelium at first stimu- lates the growth of the plant. The activities of the mycelium continue throughout the growth and development of the host until the formation of the flowers begins. In these rapidly developing embryonic tissues, the mycelium takes possession, appropriates the abundant food-substances and begins the formation of chlamydospores. The formation of these chlamydospores takes place as follows:—The mycelium in the flower at the time that spore-formation begins shows a nodulate appearance and the branches are closely fasicled like clusters of grapes. Within each swollen part of the mycelium a chlamydospore is formed. As the chla- mydospores mature, the encompassing walls of the parent-hyphae and much of the general mycelium which is not differentiated into spores, gelatinizes or otherwise breaks away and the spores are set free in large masses. Practically all the floral parts of every spikelet are destroyed, trans- forming them into the black sori of the pathogene. The smutted panicles emerge, the spore-masses ripen, and the spores are scattered when the healthy panicles are in full bloom. REPORT 1. Write a concise explanation of why the formaldehyde- treatment succeeds with loose smut of oats and fails with loose smut of~ wheat. STINKING SMUT OF WHEAT Although the loose smut is the more common on wheat in eastern United States, the stinking smut is frequently serious. In the great wheat- fields of the west it is the common and destructive wheat smut. The losses from the stinking smut may be very large, not only from the reduc- tion in yield but also from the lowering of the market-value of grain with which the smutted kernels become mixed. The life-history of the causal fungus is very different from that inducing the loose smut of wheat. SYMPTOMS Heads of wheat affected with the stinking smut are readily distinguished from the healthy heads as soon as they emerge from the leaf-sheath. Read Barrus, Phytopath. 6:21-28; study fig. 2; and the diseased and healthy specimens collected in different stages of development. NOTE :— 1. The difference in size and color of the heads. 2. On dissecting flowers, the differences exhibited by ovaries and stamens; size, color, form and odor. Confirm, so far as available material will permit, the observations of Barrus. Make a series of DRAWINGS to show the comparative morphol- ogy of diseased and healthy heads and flowers, from flowering-time to maturity. ETIOLOGY This disease is caused by TJulletia Tritict (Bjerkander) Winter, or by .- Tilletia foetens (Berkley and Curtis) Trelease, (=T. laevis Kithn). This is a case in which two distinctly different species of fungi cause the same type of disease, in fact the two species may occur together in the same ovary. It is the latter form, 7. foetens, which is most commonly found in eastern United States and will be the one here considered. These are species of the Ustilaginales, family Tilletiaceae. Life-history. This pathogene exhibits only the primary cvcles in its life-history. Since the chlamydospores usually become attached to the healthy grains during harvesting or threshing and so are almost con- tinuously associated with the living host, this smut-fungus like most others may be said to have normally no saprogenic phase. Infection from spores in the soil appears to be rare for this species. The sown wheat in the Pacific Coast regions is said to become inoculated by wind-borne spores of T. Tntict. Pathogenesis. Inoculation, as indicated above, occurs at thresh- ing-time, when spores from the crushed smutted kernels become attached to the healthy grains. Crush one of the diseased grains between thumb and finger. NOTE:— 3. The greasy character of the spore-mass. This evidently helps to attach the spores to the seed-coat. Mount a bit of the spore-mass in a drop of water. Cover and examine. OBSERVE :— 4. The numerous, more or less globose, smooth brown spores, —the chlamydospores. DRAW. 141 142 5. The chlamyvdospores of Tulletia Tritict under the demonstra- tion microscope. Note the reticulated surface of the spores, the globose shape and smaller size. DRAW. Make a mount containing chlamydospores of both Ustilago Tritict and Tilletia foetens. Compare as to size, shape, color and markings. DRAW to show the contrast. When the inoculated grains are planted, the spores of the pathogene are planted with them. The conditions which favor seed-germination also favor spore-germination. A promycelium is formed bearing sporidia which in turn produce germtubes capable of penetrating the seedling, but only at some point below the first node or tillering-point. Study the germinated spores provided, or figures in Washington Bul. 126:7, and OBSERVE :— 6. The germtube arising from the chlamydospores,—the promy- celium. From which side of the spore does it arise? 7. The cluster of sickle-shaped sporidia at the end of the promy- celium. \ 8. That frequently two of the sporidia have joined by a short tube forming an H-like figure. This is very common and was once sup- posed to be a sexual process but it is not now so considered. 9. Some of the sporidia germinated, forming secondary sporidia. Make prawincs to show chlamydospore-germination and formation of secondary sporidia, or copy from Minnesota Bul. 133, pl. XXIV and XXV. The germtubes from sporidia or secondary sporidia penetrate the seed- ling as it emerges from the grain and, branching, forms amycelitum. This mycelium quickly reaches the growing-point and grows upward with the culm causing no apparent injury to the host. At the time of flower-forma- tion, however, the hyphae develop rapidly and, growing into the ovary, destroy the contents and replace them with the black spore-mass. REPORT 1. A farmer who knows how to control stinking smut desires to understand the cause of the disease and just how it differs in this respect from the loose smut of wheat. Write him a letter giving this information in a form which he will understand. ASPARAGUS RUST This disease is of European origin, and first appeared in America in several localities along the Atlantic seaboard about 1896. It rapidly appeared farther and farther west until by 1902 it had become an important factor in asparagus-growing in California. It is much more destructive in this country than in Europe. It is the most important disease of asparagus in America. SYMPTOMS Most rust diseases exhibit themselves in some form of hypoplastic or metaplastic effect. While the very first effect of the asparagus rust is probably hypoplastic 1n character, this rapidly passes over into a necrotic condition, the host-tissues being rather quickly killed. The signs and symptoms of rust diseases group themselves about certain distinct spore- producing stages of the pathogene. In the case of the asparagus rust there are three: the cluster-cup stage, the red rust stage and the black rust stage. All of these occur on asparagus. The cluster-cup stage. The disease in this stage affects only the stalks in the young condition shortly after they come up in the early spring. Examine the specimens provided and OBSERVE :— 1. The oval-shaped, light-green patches on the canes near the base, covered with minute honey-colored pimples. These are the spermagonial fruit-bodies of the pathogene,—the pycnia. 2. On the lesions as they grow older, larger pustules arranged in concentric order within the lesions, especially definite in the older spots; averaging how many to a lesion? 3. That finally these pustules break through the epidermis and appear as round cup-shaped bodies,—the aecia, exposing the yellow spore-mass within. This phase of the disease is usually to be found only on volunteer plants along roadsides and hedgerows, on plants in abandoned plantations and in young uncut piantations. Make a prawinc to show the lesion of the cluster-cup stage. The red rust stage. This usually appears early in the summer on the plants which are allowed to grow up after the cutting-season. In the specimens provided, OBSERVE :—— 4. The rusty brown linear pustules scattered very abundantly over the stem, branches and even on the needles,—the uredinial sori or uredinia. 5. Their size, number and arrangement on the surface; relation to the host-tissues. + 6. The dusty character of their contents. 7. Any pathogenic effects exhibited by the tissues about the sori. Make a DRAWING of a diseased stem; also a DRAWING of a uiredinium as seen under the hand-lens. The black rust stage. This phase of the disease begins to develop in late summer on the same branches and needles along with the red rust stage. During the transition, affected plants take on a brown color which, however, soon gives place to a distinct black, as uredinial develop- 145 144 ment ceases and the black resting-spores of the pathogene predominate. Examine the old diseased branches and needles provided and OBSERVE :— 8. The crowded black sori or telia. How do they compare with the uredinia as to prominence, shape, size, arrangement on the stems and branches, and dustiness of their spore-masses? 9. That the host-tissues covered with the telia are dead and shriveled. This is the last phase of the disease, the autumn or winter condition of rusted plants. Make a DRAWING of a diseased stem, and also of the pustules as seen under the hand-lens. ETIOLOGY The asparagus rust is caused by Puccinia Asparagi DeCandolle, a species of the Uredinales, an order of fungi, the members of which are the most highly specialized of the Basidiomycetes. It is an autoecious patho- gene producing its different spore-forms all upon the same host. Life-history. It produces during its life-cycles all the known fruiting structures of the rusts: pycnia (O), aecia (I), uredinia (II), telia (III), and basidia (IV), each with their characteristic spores. It is therefore said to be a Eupuccinia, that is, a true Puccinia. (See McAlpine, Rusts of Australia, p. 10-11.) The Primary Cycles have their development early in the spring on the young shoots before July first; often as early as March but usually during April and May, depending upon the locality and season. Pycnia and aecia only are developed during the primary cycles. Pathogenesis. The inoculum for the primary infections consists of the basidiospores or sporidia produced on the promycelium from the overwintered teliospores on diseased stalks and needles. Examine the germinated teliospores on slides provided; or study California Bul. 165, fig. 27. OBSERVE:— 10. The long slender promycelium (basidium) put forth from each cell of the teliospore; 4-celled near the apex. 11. The long pointed sterigma from each basidial cell, bearing at its apex a thin-walled ovoidal basidiospore. Each spore contains one nucleus and finely granular protoplasm. DRAW or copy to show sporidia ready for dissemination. These sporidia are carried by the wind or splashing rain to nearby shoots just coming up. There in the moisture on the surface they send forth a germtube which penetrates the tender epidermis and gives rise to a locally spreading mycelium. From the mycelium, within less than a month, are produced first pycnia and promptly after them, aecia. Study cross-sections of the stalk (freehand or prepared) through an aecial lesion; or California Bul. 165, fig. 18. OBSERVE :— 12. The large cup-like aecia and scattered among them the minute flask-shaped pycnia (spermogonia). Locate a pycnium and study its structure under the high-power. MAKE OUT :— 13. The very slender interwoven mycelium forming the pyenial wall. 14. The long slender sporophores arising from the wall-mycelium and converging at the center of the pycnium about a small cavity which is filled with the very minute bacterium-like pycnospores (spermatia). 145 15. The protruding neck of the ostiolum through which the spermatia are discharged. These pycnospores have now no known function. They will not germinate and are supposed to be vestigial male cells (sperms). Study the aecia and OBSERVE :— 16. That they are sunken in the tissues; at first covered by the epidermis of the host. Locate one that has not burst through the epidermis. The pycnia are more superficial; subepidermal or sub- cuticular? 17. The fine interwoven mycelial threads between the host- cells about the aecia. Do they ever penetrate into the host-cells? 18. That it is from a densely interwoven mat of this mycelium that the structures of the aecium are developed; to be seen at its base. 19. The closely packed club-shaped sporophores in the base of the cup, arising from the mycelial mat. 20. The chains of spores cut off from each sporophore, forming the parenchyma-like mass that fills the cup. Why are the immature aeciospores angular in outline? Note that the maturing spores at the mouth of the aecium become globose. 21. The large cells forming a lining to the cup,—peridial cells. They also arise in chains from short mycelial branches similar to the sporophores. Note the difference in the thickness of the wall of the inner and outer faces of the cells. This lining of the cup is pseudoparenchyma- tous and is called the peridium. The mycelium of the aecial stage arises from the one-celled basidiospore, and each cell is uninucleate. When the formation of the aecium begins, there is a sexual fusion of many pairs of mycelial branches in the region of what is to be the base of the cup. From each pair of branches arises a single binucleated stalk,—a sporophore of the aecium. A chain of spores are developed from each of these binucleate sporophores by suc- cessive conjugate nuclear divisions and a laying-down of a septum between the pairs of nuclei thus formed. Examine stained sections carefully under high-power and LOCATE :— 22. The paired nuclei in the sporophores; in the aeciospores. Make a DRAWING to show the structure of the aecium, the pycnium and their relation to the host-tissues as seen in longisection. Remove with a needle or scalpel some mature aeciospores from the diseased stalks provided. If dry, mount in potassium hydroxide. Study and OBSERVE :— 23. The form, size, color, contents and markings on the epispore. DRAW several aeciospores. But one crop of aeciospores is produced. With the maturity and discharge of the last of them the activities of the primary cycle cease. The aeciospores initiate secondary cycles through which alone the patho- gene perpetuates itself until the following year. There is no saprogenesis in the primary cycle. Secondary Cycles develop on the stems, branches and needles of La affected by the aecial stage and on those of neighboring asparagus plants. Pathogenesis. The first secondary cycles are initiated by aecio- spores which fall upon the host. These germinate in the dew which forms at night and send out each a germtube which rapidly grows along 146 over the surface until its tip reaches a stoma through which it penetrates to the tissue within. The protoplasm of the spore passes out into the germ- tube keeping constantly in its tip as it grows. Within the substomatal cavity, the tip of the germtube applies itself to one of the parenchymal cells and sends into it a short blunt branch,—a haustorium. Having thus established a food relation with the host, it grows and develops a ramifying binucleate mycelium. This mycelium spreads only locally and produces within two or three weeks mature uredinia. Scrape some uredospores from a diseased stalk, mount in potassium hydroxide and OBSERVE :— 24. The form, size, color and contents of the uredospores as compared with the aeciospores; markings on the epispore if any. DRAW several aeciospores. Study cross-sections (freehand or prepared) of a stem through a ured- intum and MAKE ouT:— 25. The structure of the sorus and its relation to the host-tissue. 26. The intercellular mycelium. Are haustoria formed? (See California Bul. 165, fig. 16.) 27. The stout sporophores arising from the mycelium, each bear- ing at its apex a uredospore in some stage of development or mature. How can one tell whether the spore is young or mature? Make a DRAWING of a part of the cross-section through the uredinium. These uredospores are usually wind-disseminated and initiate other secondary cycles. They germinate at once in moisture, even in a moist atmosphere. They infect the host in a manner and under conditions simi- lar to the acciospores. The germtubes emerge through special pores or thin places in the spore-wall. Mount and examine uredospores that have been treated with acetic acid. OBSERVE :— 28. The size, number and location of the pores. DRAW. For germination and penetration into the host, study California Bul. 165, fig. 21-22. Supplement with study of germinating spores on slides, if available. Make prawincs to show the points brought out. From the mycelium produced from the uredospore, other uredinia with mature uredospores may be produced in twelve days under favorable conditions. This is repeated over and over throughout the growing-season. The mycelium remains binucleate throughout all the uredospore- generations, the spores being binucleate also. As the host begins to mature, there is developed from the mycelium in the secondary lesions, not uredospores but another spore-form,— chlamydospores, black resting-spores known as teliospores (teleutospores). They often arise at first in the same sorus with the uredospores, later they appear in sori in which no uredospores are formed. Mount some telio- spores in potassium hydroxide and stupy:— 29. Their form, size and structure as compared with the uredo- spores; color, where located, in walls or contents? 30. The thick walls and densely granular oily contents. _ 31. The light spot in the center of each cell; not always evident. The nuclei are located here. These spores are at first binucleate but at, or just before the germination the nuclei fuse and sexual fertilization, begun by the association of nuclei in the aecium, is now completed. The structure of the telium and its relation to the host-tissues does not differ materially from that of the uredinium. DRAW several teliospores to show structures and variations in form and size observed. 147 Saprogenesis. With the formation of the teliospores, the host has succumbed. The rusted twigs and needles fall to the ground while the old stalks stand erect during the winter or fall under the weight of snow. On these stalks, twigs and needles, the pathogene in the form of dormant teliospores passes the winter. Under the conditions of moisture and temperature that start the host into growth in the spring, the teliospores on the old host-debris become active. They germinate 7m situ forming a promvcelium from each cell of the spore. Four basidiospores are pro- duced on each basidium. Each is uninucleate, its nucleus having been derived through the reduction division of the fusion nucleus of the telio- spore. These sporidia, as we have seen, constitute the primary inoculum which infects the young asparagus shoots and produces the aecia. REPORT 1. Prepare a DIAGRAM showing the spore-forms, and the activi- ties of P. Asparagt DC. in proper sequence through the primary and secondary cycles. 2. Give in some detail three fundamentally different methods of controlling the rust of asparagus, arranging them in order of practicability and efficiency. Justify by explanation and argument, the position to which each method is assigned in the sequence. BLACK STEM-RUST OF CEREALS AND GRASSES There are many rust diseases of cereals and grasses. The black stem- rust is perhaps of greater economic importance than any of the others, especially on wheat. It is one of the earliest-recorded rust diseases and the subject of many researches by mycologists and plant pathologists. Early in the spring it may affect the barberry (Berberis vulgaris L.). At the same time or later in the season it appears on wheat, oats, barley, rye and many other grasses. On cereals and grasses it is characteristically a stem-rust. SYMPTOMS This disease is far more injurious to cereals and grasses than to the bar- berry. The signs and symptoms exhibited by rust diseases are associated with certain distinct spore-producing stages of the causal fungus. In the case of the black rust of cereals there are three: the cluster-cup stage, the red rust stage and the black rust stage. Cluster-cup stage. The leaves and flower-racemes of the barberry are the organs affected. Examine the leaves provided and OBSERVE :— 1. The small spot-lesions; size, location, color both above and below, and the thickening of the leaf-tissues in the lesion. The disease exhibits distinct metaplastic effects on this host; there is a slight over- growth of affected tissues. 2. With the hand-lens, the tiny dark amber or nearly biack pimples embedded in the tissues of the upper surface,—the pycnia (sper- magonia), functionless structures of the pathogene. They normally accompany or precede, in the same lesion, the aecial fruit-bodies next to be observed. 3. On the lower suabices the sunken cups, exposing their yellow spore-masses. These are the aecia or cluster-cups. Make DRAWINGs to show the cluster-cup symptoms on both surfaces of the leaf. Examine the diseased flower-clusters. OBSERVE :— 4. The swollen and malformed flowers and pedicels; color of - the affected organs. 5. The abundantly developed aecia. Are pycnia present? SKETCH a diseased flower cluster. Red rust stage. Examine the specimens of diseased wheat or oats provided and OBSERVE :— 6. The large reddish yellow pustules scattered over the leaf- sheaths,—the uredinia; not usually so common nor so numerous on the blades. 7. The size, arrangement and relation of these pustules to the host-tissues. Note the torn edges of the epidermal covering and the dusty spore-mass of the ruptured uredinia. 8. The effect on the host-tissues; color effects. SKETCH a rusted leaf-sheath to show the symptoms of the red rust stage. Make a DRAWING of one of the uredinia as it appears under the hand-lens. Black rust stage. This develops during the latter part of the growing- season along with the red rust stage so that the two are often observed together on the leaf-sheaths and stems. In the material provided, OBSERVE :— 148 149 9. The large black linear sori extending up and down the stem,— the telia. Most of them have ruptured the epidermis, exposing the black spore-mass within. 10. The thin epidermal covering, ruptured in most of the telia but partially or wholly covering others. 11. The telia developed on the inflorescence. What organs are affected? 12. Kernels from badly diseased plants in comparison with those from healthy plants. How do they appear to be affected? Telial sori are occasionally developed under the seed-coat of the kernel. (See Phytopath. 1:150-154, fig. 1-2.) SKETCH an internode and also parts of the inflorescence to show the black rust symptoms. Make an enlarged DRAWING of a telium as seen under the hand-lens. ETIOLOGY The black rust of cereals and grasses is caused by the fungus, Puccinia graminis Persoon. It is one of the Uredinales which are perhaps the most highly specialized of basidiomycetous pathogenes. It is a heteroecious parasite producing its aecial structures on the barberry, a host widely remote in relationship from its grass-hosts on which the other spore- forms appear. This species, Puccinia graminis, includes a variety of biologic forms, morphologically alike, and all having their aecia on the barberry but restricted rather sharply in their uredinial and telial stages to definite cereal- or grass-hosts. (See McAlpine, Rusts of Australia, Rk.) Life-history. This pathogene produces, during its life-history, all the known fruiting structures of the rust-fungi: pycnia (O), aecia (I), uredinia (II), telia (IIT), and basidia (IV), each with their characteristic spores. It is therefore said to be a Eupuccinia, that is, a true Puccinia. (See McAlpine, Rusts of Australia, p. 10-11.) The Primary Cycles are normally those which develop only upon the barberry and exhibit the pycnia and aecia. It seems certain, however, that the fungus may winter over in the uredinial form (probably as my- celium) and by uredospores initiate primary infections on grass- and cereal-hosts. This second type of primary cycle is essentially secondary in all respects except as to the time it originates. It will not be considered separately in this exercise. Pathogenesis. The inoculum for the primary infections consists of the basidiospores (sporidia), produced on the basidium (promycelium) from the overwintered teliospores on diseased straw. Examine the germinated teliospores on slides or study the drawings provided, and OBSERVE :— 13. The long slender basidium put forth from each cell of the teliospore; 4-celled near the apex. 14. The long pointed sterigma from each basidial cell bearing at its apex a thin-walled ovoidal basidiospore (sporidium). Each sporidium contains one nucleus and finely granular protoplasm. DRAW or copy to show sporidia ready for dissemination. These sporidia are carried by the wind or splashing rain to nearby bar- berry bushes where, in the moisture on the surface, they send forth a germ- tube which penetrates the tender epidermis and gives rise to the locally 150 spreading mycelium. From the mycelium, within less than a month, are produced first pycnia and promptly after them, aecia. Study cross-sections of the leaf (freehand or prepared) through an aecial lesion. OBSERVE :— 15. The large cup-like aecia and opposite them on the upper surface of the leaf, the minute flask-shaped pycnia (spermagonia). Locate a pycnium and study its structure under high-power. MAKE OUT :-— 16. The very slender interwoven mycelium forming the pycnial wall. 17. The long slender sporophores arising from the wall-mycelium and converging at the center of the pycnium about a small cavity which is filled with very minute bacterium-like pycnospores (spermatia). 18. The protruding neck of the ostiolum through which the spermatia are discharged. These spermatia have now no known function. They will not germinate and are supposed to be vestigial male cells (sperms). Study an aecitum and OBSERVE :— 19. That it is sunken in the tissues; at first covered by the epidermis of the host (see one that has not burst through). The pycnia are more superficial; subepidermal or subcuticular? 20. The fine interwoven mycelial threads between the host- cells about the aecia. Do they ever penetrate into the host-cells? 21. That it is from a densely interwoven mat of this mycelium (to be seen at the base) that the structures of the aecitum are developed. 22. The closely packed club-shaped sporophores arising from the mycelial mat in the base of the cup. 23. The chains of spores cut off from each sporophore, forming the parenchyma-like mass that fills the cup. Why are the aeciospores here angular in outline? Note that the maturing spores at the mouth of the aecium become globose. 24. The large cells lining the cup,—peridial cells. They also arise in chains from short mycelial branches similar to sporophores. Note the difference in thickness of the wall of the inner and outer faces of the cells. This lining of the cup is pseudoparenchymatous and is called the peridium. The mycelium of the aecial stage arises from the uninucleate sporidium and each mycelial cell is uninucleate. When the formation of the aecium - begins, there is a sexual fusion of many pairs of mycelial tips in the region where the base of the cup is to be. From each pair of branches arises a single binucleate stalk,—a sporophore of the aecium. A chain of spores is developed from each of these binucleate sporophores by successive conjugate divisions of the paired nuclei and the laying-down of a septum between the resulting pairs thus formed. Examine stained sections carefully under high-power and LOCATE :— 25. The paired nucleiin the sporophores; in the aeciospores. Make a DRAWING to show the structure of the aecium, pycnium and their relation to the host-tissue as seen in section. Remove with the needle or scalpel some mature aeciospores from the cups on diseased leaves provided. If dry, mount in potassium hydroxide. Study and OBSERVE :— 26. Their form, size, color and contents; markings on the epispore. DRAW several aeciospores. 151 But one crop of aeciospores is produced. With the maturity and discharge of the last aeciospores, the activities of the primary cycles cease. The aeciospores initiate secondary cycles on the cereal-hosts through which the pathogene perpetuates itself until the following year. There is no saprogenesis in the primary cycles. Secondary Cycles, especially the late ones, develop chiefly on the leaf-sheaths and stems of the wheat, oats or grass-hosts. Leaves may also become infected. ee Pathogenesis. The first secondary cycles are initiated by aecio- spores which, falling upon the host, germinate in the dew or raindrops sending out a germtube which rapidly grows along over the surface until its tip reaches a stoma through which it penetrates to the tissues within. The protoplasm of the spore passes out into the germtube keeping con- stantly in its tip as it grows. Within the substomatal cavity, the tip of the germtube applies itself to one of the parenchymal cells and sends into it a short blunt branch,—a haustorium. Having thus established a food-relation with the host, a binucleate ramifying mycelium is developed. This mycelium produces mature uredinia within two or three weeks. Study cross-sections (freehand or prepared) of a stem through a uredi- nium and MAKE OUT:— 27. The structure of the sorus and its relation to the host-tissue. 28. The intercellular mycelium. Can the globose haustoria be found? 29. The stout sporophores arising from the mycelium, each bearing at its apex a uredospore in some stage of development, or mature. How can one tell whether the spore is young or mature? Make a DRAWING of a cross-section through the uredinium. Scrape some uredospores from a diseased stalk; mount in potassium hydroxide and OBSERVE -— 30. The form, size, color and contents of the uredospore as compared with the aeciospores; markings on the epispore, if any. These uredospores are usually wind-disseminated, initiating other secondary cycles. They germinate at once in moisture, even in a moist atmosphere. They infect the host in a manner and under conditions similar to the aeciospores. The germtubes emerge through special pores or thin places in the spore-wall. Mount and examine uredospores that have been treated with acetic acid. OBSERVE:— 31. The size, number and location of the pores. DRAW. For germination and penetration into the host, study illustrations provided. Supplement this with a study of germinating spores on slides, if available. Make prRAWwINGs to show the points brought out. From the mycelium produced from the uredospore, other uredinia ’ with mature uredospores are produced. This may be repeated seven or eight times during the growing-season. The mycelium remains binu- cleate throughout all the uredospore-generations, the spores being binu- cleate also. As the host begins to.mature, there is developed from the mycelium in the secondary lesions, not uredospores but another spore-form,— chlamydospores, black resting-spores known as teliospores (teleutospores). They often arise at first in the same sorus with the uredospores, later they 152 appear in sori in which no uredospores are formed. Mount some teliospores in potassium hydroxide and stupy :-— 32. Their form, size and structure as compared with uredospores; color, where located, in walls or contents? 33. The thick walls and densely granular oily contents. 34. The light spot in the center of each cell; not always evident. The nuclei are located here. These spores are at first binucleate but at, or just before germination the nuclei fuse and sexual fertilization, begun by the association of nuclei in the aecitum, is now completed. The structure of the telium and its relgtion to the host-tissue does not differ materially from that of the uredinium. DRAw several teliospores to show structure and variations in form and size observed. Saprogenesis. With the ripening or death of the host, teliospores have been formed usually in great abundance on the straw. When the grain is harvested, many teliospores are left on the stubble. Those on the straw go with it into the stack, then into the manure pile and finally with the manure back on the land. Under the conditions of moisture and temperature that starts the barberry into growth in the spring, the teliospores on the old straw become active. They germinate 7m situ form- ing a promycelium from each cell of the spore. Four basidiospores are produced from each basidium. Each is uninucleate, its nucleus having been derived through the reduction division of the fusion nucleus of the teliospore. These sporidia, as we have seen, constitute the primary inocu- lum which affects the young leaves of the barberry. They cannot, so far as is known, affect any of the cereals or grasses. REPORT 1. Prepare a diagram showing the spore-forms and activities of Puccinia gramints Pers. in their proper sequence through the primary and secondary cycles. 2. Explain the effect of the black stem-rust on the tissues of its host, and point out how it causes reduction in yield. CARNATION RUST This is a disease of European origin, which was first observed in this country in 1890. It rapidly developed in epiphytotic form, shortly appear- ing in every carnation house throughout eastern United States. It was for a decade the most destructive and most feared of carnation diseases, but is now enphytotic and rarely’ serious, due to the development of resistant varieties. It also affects some other species of the genus Dianthus and species in related genera. In Europe the cluster-cup stage of this disease is known, affecting Euphorbia gerardiana Jacq. SYMPTOMS Since the cluster-cup stage of the carnation rust 1s unknown in America, the disease will be studied only as it appears on the common greenhouse carnation. The red and black rust stages appear together and are so much alike that the symptoms they induce will be considered together. Both leaves and stems are affected. Study the materials provided and OBSERVE :-— 1. The pale-green or yellowish areas on the leaves; which surface ’ 2. In some of these spots, dark-brown or black pustules,— sori of the pathogene. The lighter-colored ones are uredinia, the darker ones, telia. 3. The arrangement of these sori within the lesion; scattered, confluent, linear? 4. Some of the sori burst open exposing the dark-colored rusty spore-mass within; the ruptured epidermis forming a papery fringe. 5. The sori on the stems; usually darker than those on the leaf. Stem-sori are largely telia. 6. The general effect of the disease on badly rusted plants. Make pRAWINGS to show the characters of the lesions on leaves and stems. ETIOLOGY The causal organism is a urediniaceous fungus, Uromyces Caryophy- llinus (Schrank) Winter. It is heteroecious, having all the spore-forms characteristic of the rust-fungi. Life-history. Being in this country a parasite of a greenhouse-crop, the fungus is able to propagate itself continuously through secondary cycles. The primary cycle therefore will not be here considered. The Secondary Cycles are all initiated by uredospores from sori on leaves or stems of living plants (except of course when aeciospores occur). They are constantly being initiated as uredospores are matured and disseminated. Scrape some of the uredospores from a sorus; mount and study. OBSERVE -— 7. The form, size, color, thickness of wall and markings on the epispore. Treat some with acetic acid and see if the number and arrange- ment of the germpores can be determined. DRAW several uredospores. These uredospores are scattered by wind or splashed, in watering, to nearby healthy leaves and plants. They germinate very readily in water. Examine the germinating spores on the slides provided. OBSERVE:— 153 154 8. The number of germtubes produced from each spore. Are they septate? 9. The densely granular protoplasm crowded into the tips of the long germtubes. The empty germinated spores. Compare with these not germinated. DRAW two or more germinated uredospores. The germtube enters through a stoma and forces its tip between the palisade-cells, sending haustoria into them, thus establishing a food-rela- tion with the host. Make thin cross-sections of a leaf through a sorus; clear in chloral hydrate; study and OBSERVE :— 10. The intercellular mycelium; often in gnarled and inter- woven teshes, especially in the intercellular spaces, prying apart and isolating the host-cells; densely granular, septate. 11. The peculiar lobed haustoria in the host-cells; their very thin walls and densely granular protoplasm. 12. The uredinium; its structure and relation to the host- tissue. 13. The matted mycelial bed from which arise the short closely crowded uredosporophores. 14. The globose uredospores; thin walled, covered with short spines and much lighter colored than the one-celled teliospores, some of which are usually to be found in a uredinium. Make a DRAWING of a portion of a cross-section to show the pathogene- structures and their relation to the host-tissue. The mycelium is supposed to spread very generally throughout the leaf- and stem-tissues beyond the point where distinct lesions appear, so that cuttings from diseased plants are usually invaded. It is believed that this habit of the pathogene is responsible for its wide and rapid distri- bution in this country. Make thin sections through the leaf at some dis- tance from the lesion; clear in chloral hydrate; examine and DETERMINE :— 15. Whether or not mycelial invasion is general. Select a dark-colored sorus,—a telium (usually more abundant on stems); mount some of the teliospores. Study and OBSERVE:— 16. That they are much darker in color than the uredospores, although of about the same size and shape; walls slightly thicker, and epispore nearly or quite smooth; stalk often still attached. DRAw several. The teliospores arise from the same mycelium on which uredospores are produced, usually more abundantly in the sori formed as the affected organ grows older. Saprogenesis. The teliospores do not germinate at once as do the uredospores, but require a period of rest. They are chlamydospores, and, under natural conditions, germinate in the spring producing a promy- celium with four sterigmata, each bearing a basidiospore (sporidium). Study the drawings provided. copy. These sporidia produced by the germination of the teliospores can, so far as known, infect only the Euphorbia host. As Euphorbia gerardiana does not grow in this country, the sporidia cannot function in the propaga- tion of the pathogene, and primary cycles cannot develop. REPORT 1. Prepare a diagram showing the complete life-history of Uromyces Caryophyllinus (Schr.) Wint. as it may occur in Europe. DODDER The term dodder is applied as a common name to the pathogenes as well as to the diseases which they cause. I¢ is used for all the diseases caused by species of phanerogamous parasites of the genus Cuscuta. The different dodder diseases are often distinguished by adding the host- name as, alfalfa dodder, clover dodder and the like. The pathologic effects are in all cases similar. SYMPTOMS All parts of the host above ground, especially the stems, are directly attacked by dodder pathogenes. The most striking sign is the dodder parasite itself. The tangled yellow stems matted about its host form conspicuous yellow patches in the field. These doddered areas, often several feet in diameter, are at first more or less circular. Examine the photographs showing spots in the field. OBSERVE :— 1. The dwarfed and dying host-plants at the center of the dod- dered area. 2. The densely matted dodder stems. 3. The long spreading runner-like dodder stems about the margins of the area, extending out among the healthy plants. Examine the specimens provided and OBSERVE :— 4. The yellow dodder vine entwined about the host-stems; size, color, shape in cross-section, branching. 5. Evidences of injury to the host, to be detected by comparison of diseased and healthy plants; dwarfing and chlorosis. Make a DRAWING to show the general appearance of a dodder-affected plant. ETIOLOGY Dodder diseases are caused by species of Cuscuta, a genus of the family Convolvulaceae. Some near relatives in the same family are the morning- glories, bindweeds, buckwheat and sweet potatoes. There are about ninety species of Cuscuta, of which about half occur in America. The most common one on cultivated crops like clover and alfalfa is Cuscuta epithymum Murray, a species introduced from Europe. Life-history. This pathogene has an annual life-history. It is known, however, that it commonly overwinters in a vegetative condition on perennial hosts like clover and alfalfa. (See N.Y. (Geneva) Bul. 305: 369- 374.) The Primary Cycles are initiated by the seeds which have lain on the ground over winter. ‘ Pathogenesis. Examine seed of C. epithymum. NOTE:— 6. Their surface markings; color; and that the one side is convex while the other is flattened in two or more places. Measure several. DRAW:—(a) several to show variations in size and form; (b) two seeds greatly enlarged showing all their characteristics. Describe the color in the notes on the margin of the paper. 7. Examine the seed of the other species provided. ‘These may all occur on clover or alfalfa. Make enlarged prawincs of each so that they will be comparable in size with those of the drawings of C. epithymum. 155 156 8. The embryo is coiled in the seed and imbedded in the food substance. Examine the photographs of plates taken from Koch’s work. DRAW. 9. If available, examine the dodder seedlings and note how they first attack the host-plant. Examine N. Y. (Geneva) Bul. 305, pl. 3, and Koch’s pl. 1, fig. 1-3. Make prawincs to show the characters of the seedling and its method of attacking the host. : ’ As soon as the seedling has attached itself to the host, the vestigial root by which it was anchored in the soil, shrivels and dies. The twining stem, however, feeds on the host, grows rapidly and by branching spreads to neighboring hosts. Study the dodder plant on the host pro- vided. OBSERVE :— 10. The type of branching; opposite or alternate? 11. The leaves; their location, size, shape, color and abundance. How are these foliage conditions to be accounted for? Untwine and separate a portion of the dodder thread from the host- stem. OBSERVE :— 12. That it is attached at some points. At such places the spirals are shorter and are tight about the stem. 13. With the hand-lens, the rows of minute punctures in the host-stem where the dodder was attached; the oval depression about each. 14. With the hand-lens, the corresponding row of concave sucker-like disks on the dodder stem,—the attachment-disk; the minute elevation at the center of each disk,—the broken-off haustorium. 15. The aborted haustoria in places along the dodder stem where it failed to come in contact with the host. Make a DRAWING of a portion of a host-stem with entwined dodder to show all the points brought out in 10-15. Cut thin cross-sections through the clover and dodder stems at the point where haustoria are attached. Cover and examine under the low-power. OBSERVE :— 16. In the clover stem, the large pith, the vascular cylinder, the cortex, and the epidermal layers. In the vascular cylinder, note the — xylem containing the large ducts, and the phloem which consists of soft sclerenchyma within and the lighter area of sclerenchyma-fibers without. 17. In the dodder stem, the haustorium. Note the shape of the attachment-disk in cross-section; its relation to the haustorium; where the haustorium arises and how it penetrates the host. Note what happens where it comes in contact with the sclerenchyma-fibers. Toward which tissue of the host-stem does it grow? Why? Note the spiral ducts in the center of the haustorium. Make diagrammatic DRAWINGS of the host-stem and the dodder stem to show the relative sizes and relation of parts. With the low-power, examine the stained longitudinal sections of the haustorium of dodder on Impatiens (touch-me-not). NOTE:— 18. The long thread-like cells extending out from the tip and sides of the haustorium into the cortex, pith, and sometimes into a bundle, making a connection with a conductive vessel of the host. 19. The layer of crushed cells at the point where the haustorium emerges from the dodder stem. Does the epidermis of the dodder con- tinue about the haustorium? What becomes of it? Are the cells of the host crushed? What is the function of the thread-like cells? 157 DRAW a single haustorium showing the type of cells in the center and at the ends; the connection of the host and the dodder. Toward autumn flowers may be developed on the dodder vine. Study a fruiting branch of the dodder and OBSERVE :— 20. The compact flower-clusters. Where do they seem to be most commonly formed? How many flowers in a cluster? 21. Under the hand-lens, the scale-like leaf at the base of each flower-cluster and at the base of each flower. DRAW a single flower-cluster enlarged three times. Dissect and study a single mature flower. NOTE :-— 22. The structure and arrangement of the calyx, corolla, sta- mens with fringed scale at the base of each, and the pistil. How many parts of each? DRAw a single flower enlarged, with calyx and corolla removed at one side. Cut across the ovary, examine with hand-lens and DETERMINE :— 23. How many carpels and ovules are produced. DRAW. Examine the matured capsule. How does it compare in size with the flower? How many seeds does it contain? Note the remnants of the calyx or the corolla at the base. From what does the capsule develop? DRAW. Saprogenesis. The seeds fall to the ground where they le dor- mant until the following spring. They germinate when conditions favor- able to the growth of the host prevail. The vestigial root serves as an anchorage for the simple slender seedling, probably taking up only water from the soil. The seedling seems to be dependent largely on food stored in the seed, although chlorophyl is slightly developed. Seed germination and contact of the seedling with its host completes the pri- mary life-cycle. Secondary Cycles may be initiated during the growing-season by pieces of dodder stems broken off in cutting and harvesting the host, and falling upon healthy plants, infecting them. Pieces of dodder stems are very tenacious of life and thus afford a dangerous inoculum for spreading the pathogene in cultivated crops. The spreading of the pathogene from one individual host-plant to a neighboring one may also be regarded as a type of secondary infection. REPORT 1. A farmer had a few spot-infections in an alfalfa field. After cutting the hay, the ground where the dodder occurred was spaded. Soon, however, the dodder appeared about the margins of the same areas. Write a letter outlining the measures to be taken to prevent further local spread of the pathogene and its dissemination over the field. 2. Give directions for determining whether or not there is dodder in the alfalfa seed, and if present, how to get rid of it. TOBACCO MOSAIC This is a disease not only of tobacco but also of many other solanaceous plants. Plants affected with the mosaic disease, or as it is often called, calico, mottled-top, grey-top, or frenching, do not usually die. There is pro- nounced hypoplasia, especially of young leaves. There is a reduction in size, and chlorophyl-development is halted, so that a true chlorosis results. SYMPTOMS The leaves, and sometimes the branches, are the only organs of the host which exhibit symptoms. The plants are often much dwarfed and, in the case of Nicotiana rustica I.., are sometimes killed. In some of the so- called immune varieties, it has been found that a progressive rotting of the tissues follows inoculations with the virus, but in such cases there are none of the usual symptoms of the disease. (U.S. Agr. Dept. Bul. 40:2.) The symptoms vary from small blisters on the leaves, or the distinct dark-green islands in large areas of yellow, to an excessive suppression of the development of the lamina of the leaves, in which only the midrib remains normal. On the entire plant. Study the diseased and healthy tobacco plants provided. OBSERVE :— 1. The comparative size and appearance of the healthy and diseased plants. SKETCH or copy from U.S. Agr. Dept. Bul. 40, pl. VII. Maintain relative proportions between the healthy and diseased plants. On the leaves. Examine the plants provided and locate, but do not remove, leaves showing various symptoms. OBSERVE :— 2. The characters of a healthy leaf, its regularity of surface and margin; its size. DRAW. 3. The peculiar green and yellow blotched appearance of diseased leaves. Note the blister-like elevations on the upper surface. Are they swellings or are they archings of the leaf? In which areas do they occur? Is there any relation between the veins and the green areas? 4. That the yellow areas of the leaf are apparently thinner than the green islands. 5. The comparative size of healthy and diseased leaves of the same age. DRAW a diseased leaf on the same scale as the healthy leaf. Bring out in the drawing and labeling as many of the characters as possible. 6. The distorted leaves. These may be long and ribbon-like or the lamina of the leaf may be entirely undeveloped, although the mid- rib is not affected. DRAw, orcopy U.S. Agr. Dept. Bul. 40, pl. II, fig. 1. 7. That certain upper leaves may show a mottling (green and yellow) but without the accompanying distortions of the surface. Note how the green areas follow the veins. This is the phase that gives the names, grey-top and mottled-top, and occurs when the plant becomes infected just as the immature flower-heads appear. DRAw, or copy U. Ss. Agr. Dept. Bul. 40, pl. I, fig. 2. On the blossoms. Examine the flowers of the plant provided, or U. S. Agr. Dept. Bul. 40, pl. III and IV. Various species of Nicotiana 158 159 are shown. Note particularly the pink-flowered form of N. Tabacum L. and N. paniculata, if available. OBSERVE :— 8. The mottled or blotched appearance of the corollas of N. Tabacum. Note the variations and compare with the flowers of healthy plants. 9. That some. of the flowers show a depauperate growth of the corolla; the stamens and stigma extrude. 10. That the buds may be depauperate and variously mis- shapen. 11. That the corolla-tubes of N. paniculata are bent and crump- led. Make pRrAwINGs of flowers and buds, both healthy and diseased, to show the various symptoms. Indicate all points, which cannot be shown in drawings, by notes in the margin. On tomato leaves. Examine the tomato plant and OBSERVE :— 12. The mottling of the leaves; their texture and flexibility; their size and shape. pRaw and note characters in the labeling. On petunia leaves. OBSERVE:— 13. Their color, size and flexibility. DRAW and label fully. The symptoms on other hosts are similar to these. ETIOLOGY The cause of this disease is unknown but there are various theories formulated to explain it. Some investigators (Woods, Chapman and others) believe that enzymes play an important, if not the primary, part in causing it; oxidase and peroxidase are specifically named. It is said that rough handling of the plants, such: as breaking the roots in transplanting or severe pruning of the tops, will cause the disease. Disturbance of the equilibrium between root-absorption and leaf-transpiration is also held to be responsible for mosaic. A much more plausible theory is that recently offered (by Allard and others). The disease is attributed to a filterable virus. It is held that this virus consists of an ultra-microscopic organism, bacterial or proto- zoan in nature. The extreme minuteness or plasticity of the organism probably allows it to pass through the pores of the Chamberland filter. Such phenomena are known in other cases. Crush small pieces of healthy and diseased tobacco leaves in small drops of water, cover, and examine each with the high-power. OBSERVE :— 14. The absence of any evidence of an organism in the diseased tissues. Pathological Histology. The effects on the structure of the leaf are very pronounced. Make thin cross-sections through diseased and healthy tobacco leaves, or if available study prepared slides. OBSERVE :— 15. The arrangement and contents of the cells of the palisade- layers, spongy parenchyma and epidermal tissues of the healthy leaves. DRAW in detail a section across the leaf. 16. The corresponding cells in the green and yellow area of the diseased leaf. Note the suppression of the palisade-tissue in the yellow areas. The relative thickness of the green and the yellow areas. DRAW a section across a diseased leaf at the same enlargement as for the section across the healthy leaf. 160 Pathogenicity Studies. Although the cause of the disease is not known, it is very easy to inoculate and obtain infections with the virus. A series of infection-experiments will be undertaken by the class as follows: General instructions. Students will work in pairs, A, B and C, as assigned by the instructor. There will be four experiments, each involv- ing the cooperative action of three pairs of students. Two pairs in each experiment will inoculate the healthy plants provided as directed, while the third pair will prepare check-plants. Healthy tobacco, tomato and petunia plants will be provided. Do not touch these plants except when directed and then exactly as directed. Experiment I. Inoculation by touching. PROCEED as follows:— 17. Thoroughly wash the hands and disinfect in alcohol pro- vided. 18. Pairs A and B, squeeze and rub but do not crush, between thumb and finger, a diseased tobacco leaf; then immediately squeeze and rub with the same thumb and finger, leaves on the healthy plants. LABEL. 19. Pair C, do not touch diseased plants but squeeze and rub with thumb and finger (do not crush), the leaves on the healthy plants provided for checks. LABEL. Experiment II. Incculation with sap from diseased planis. — PRO- CEED as follows:— 20. Pairs A and B. Each pair will thoroughly clean and rinse a mortar in sterilized distilled water. Grind three diseased tobacco leaves in a little sterilized distilled water in the mortar. The virus is thus freed from the leaf-tissue. Then very thoroughly wash the hands and disinfect in alcohol provided. Flame and cool a needle. Dip the point into the virus and prick the midrib of several young leaves of the healthy plants provided. Dip the needle each time before pricking. LABEL. 21. Pair C, thoroughly wash the hands and disinfect with alcohol. Do not touch diseased plants. Flame and cool a needle. Dip it in sterilized distilled water and prick the midrib of several young leaves of the healthy plants provided. LABEL. Experiment III. Root inoculation. PROCEED as follows:— 22. Pairs A and B, thoroughly wash the hands and disinfect with alcohol provided. Do not touch the tops of the plants. Sterilize a scalpel by dipping in alcohol and flaming. Thrust the scalpel into the soil about the healthy plants provided, so as to cut some of the roots. Pour into the soil, where the roots were cut, some of the diseased-leaf extract prepared by pairs A and B in experiment IJ. LABEL. 23. Pair C, thoroughly wash the hands and disinfect with alcohol. Proceed as in number 22 but use sterilized distilled water to pour on the roots, instead of the diseased-leaf extract. LABEL. Experiment IV. Inoculation through wounds. PROCEED as follows:— 24. Pairs A and B, thoroughly wash the hands and disinfect in alcohol provided. Break a young leaf from each of the healthy plants provided. Rub a diseased leaf between thumb and finger and touch the broken leaf-stub on the healthy plants but do not touch them elsewhere. LABEL. 25. Pair C, thoroughly wash the hands and disinfect with alcohol. Do not touch diseased plants. Break a young leaf from each 161 healthy plant provided. Rub the healthy leaf between thumb and fingers and touch the broken leaf-stub with the finger. LABEL. These plants will be kept in the greenhouse and are to be examined every two days for two weeks. Make notes on the first appearance of the dis- ease, 1. e. (a) the number of days since inoculation; (b) the maturity of the infected leaves; (c) whether or not inoculated piants show infection. After two weeks, the plants will be returned to the laboratory for final notes. At this time a tabulation-sheet of the results recorded will be made to obtain the class-result on the different types of inoculation. REPORT 1. Give the class-record of the inoculation-experiments. 2. State the various ways that the virus can be disseminated. What precautions should be taken to prevent dissemination. Explain. METAPLASTIC DISEASES SPONGOSPORA SCAB OF POTATOES This slime-mold disease has come into considerable prominence in recent years because of its discovery in the seed-growing potato-sections of northern United States and Canada. It appears to be confined to the | potato. Soil and climatic conditions seem to greatly limit the geographical range of the disease. It is evidently a disease of cool, temperate climates or high table-lands and valleys. SYMPTOMS The lesions of this disease are confined to the underground parts of the host; tubers, roots and stolons (rhizomes). On the tubers. Three types of lesions are to be found on the tubers; the scab (the most common form), the wart-form and the canker-form. Scab-form. Examine the specimens labeled ‘“‘young sori.” OB- SERVE :— 1. The small brownish spots (ringed with India ink). These are the first evidences of the disease. 2. The smooth, brown mounds (also ringed with ink),—the covered sori of the pathogene. 3. The crater-like openings of some of the sori; they are mature and are opening for spore-dispersal; form, size and color of the sori. Examine the specimens labeled ‘‘mature sori.’”? OBSERVE :— 4. The large open brown sori. Note the torn and upraised cuticle about the margin. 5. The brown powder within the sorus. Pick it out with the needle. 6. The empty depressions left after this powder is disseminated. Make a DRAWING of the entire tuber to show the sori and their distri- bution. Make a series of enlarged DRAWINGS (at least four), showing the ap- pearance of the sori in different stages of development. Wart-form. This form is not common but may develop in severe cases in moist soils. Read Maine Bul. 227:94, and study figure eit or study aes if available. OBSERVE :— That the lesions are more or less confined to the seed- or eye- end of nak tuber. 8. That they are much more enlarged and gall-like than the ordinary scab-form. How does the location of the lesions help to explain their warty character? SKETCH a tuber showing the wart-form of the disease. Canker-form. Where the lesions are numerous and coalesce, the tubers may show, in an advanced stage of the disease, large deep cankers. This is held by some to be the result of secondary activities of the pathogene. (See Kunkel, Jour. Agr. Research 4:237.) Study the 162 163 illustration specimens provided; Maine Bul. 227, fig. 44; and U.S. Agr. Dept, Bul) 822 pl. LIL. opsERVE— 9. The large open cankers, extending deeply into the tuber and lined with the dead and decaying tissues of the host. DRAw a tuber showing this form of lesion. On the roots and stolons. Study the specimens provided. OBSERVE:— 10. That here the lesions are gall-like in appearance; form and size; relation to the root or stolon, i.e. on the side only or involving the entire diameter? DRAW. Comparative studies. There are a number of scab-like diseases of potato tubers, the lesions of which are more or less alike. A brief examina- tion of the more common tuber diseases, in comparison with the Spongo- spora scab-lesions, is important. Examine, so far as available, the speci- mens and illustrations of the FOLLOWING :— 11. The black-wart disease. In addition to specimens and illustrations provided, study Pl. Ind. Bur. Cire. 52, pl. I-II. sKketcu a tuber to show the character of the lesions of this disease. 12. The common scab. Note the slightly raised irregular corky scab-spot. If this disease is serious, the tuber may be much checked and cracked. DRAW. 13. Silver-scurf. This disease does not cause a distinct scab; at most there is but a wrinkling or sloughing-off of the epidermis. (See Schultz, Jour. Agr. Research 6:345-346.) 14, Black scurf or Rhizoctonia scab and canker. This disease is very common but not often directly injurious to the tubers. Note the small dark-brown or black sclerotial bodies of the fungus scattered over the tuber. It is held by some that checking of the surface and even the formation of deep cankers are sometimes symptoms of this disease. (See specimens or Maine Bul. 230, fig. 71-73.) Make prRawincs to show the tuber-symptoms of this disease. ETIOLOGY The Spongospora scab is caused by the myxomycete, Spongospora subterranea (Wallroth) Johnson. It is generally distributed throughout northern Europe, Canada and northeastern United States. It is a native et South America where it occurs as a pathogene of the potato in its native ome. Life-history. This slime-mold does not differ materially from the saprophytic myxomycetes in its structure and life-history, except in so far as it has been modified by its parasitic habit. Primary Cycle. Spore-balls in the soil constitute the source of inoculum for the primary infections. The spores may apparently remain dormant in the soil for several years. Remove some of the spore-mass from a sorus on the tuber provided; mount in potassium hydroxide and OBSERVE :— 15. The rather large dark spore-balls; color and structure. Each cell of the spore-ball is a spore. DRAW. Pathogenesis. The spores in a single spore-ball all germinate at about the same time. There emerges from each cell of the spore-ball, a single, usually uninucleate ameba. (See Kunkel, Jour. Agr. Research 4,° pl. XXXIX, fig. 1-2. copy). 164 These amebae soon fuse to form a small plasmodium which penetrates through and between the epidermal cells of the tuber. If conditions are not favorable to the formation of a plasmodium, the individual amebae may encyst. Later, when conditions become favorable, each protoplast escapes from its cyst-wall through a hole and may fuse with others to form the plasmodium. Once within the tissues, the plasmodium spreads out under the epidermal tissues and down between the cells of the cortex. Study the prepared slides provided; or Jour. Agr. Research 4, pl. XX XIX, fig. 3-5, and pl. XL. jOBSERVE— 16. The densely granular protoplasm of the plasmodium in the intercellular spaces just beneath the epidermal layers. 17. The pseudopodia-like extensions of the plasmodium, forcing their way down between the cortical cells. The middle-lamella is dis- solved and the cells are forced apart. The walls become soft and swollen. 18. That the pseudopodia penetrate the cell-walls and portions of the plasmodium enter; these become separated from the main body of the plasmodium. Make a DRAWING to show the invading plasmodium, outlining the adjacent host-cells. After a certain period of feeding, all the plasmodia in the host-cells of a particular lesion simultaneously form spore-balls. Examine prepared sections through sori showing mature spore-balls; or study U. S. Agr. Dept. Bul. 82, pl. I. oOBSERVE:— 19. That the entire plasmodium is converted into spores. The host-cell serves as a sporangium. 20. The average number of spore-balls in a host-cell. 21. Remnants of the host-protoplast; nucleus, starch-grains, or cytoplasm. 22. Host-cells in which spore-formation is incomplete. Com- pare nuclei and cytoplasm of the pathogene and host. Make enlarged and detailed pRawincs of the host-cells, (a) containing plasmodia; and (b) containing mature spore-balls. Saprogenesis. What takes place after the spore-balls are set free in the soil is not certainly known. They probably germinate very shortly, the amebae passing out into the soil where they either form a plasmodium or encyst separately. Whether the organism can live a true saprophytic life in the soil is not known. It has, however, been cultured on artificial media. Secondary Cycles probably occur, as the spores can apparently germinate as soon as they are mature. The phenomena of the secondary cycles are probably the same as those of the primary cycles. A peculiar type of secondary infection of the deeper tissues of the tuber, surrounding a mature sorus, has recently been described as the cause of the canker- form of the disease. (See Kunkel, Jour. Agr. Research 4:272-273.) Pathological Histology. There is a marked stimulation of the host- tissues by Spongospora subterranea, as may be seen by the comparative study of the cells in the diseased and healthy regions of the tuber. Cut thin cross-sections (or use prepared slides) through the healthy potato skin. Examine and OBSERVE :— 23. The single layer of thin cells on the outside,—the epidermis, overlaid by the brown cuticle. 165 24. Beneath the epidermis the layers of the cells which are regularly rectangular in shape. This is the corky hypodermis. The epidermis and hypodermis constitute the skin of the potato. 25. That from the hypodermis there is a rather abrupt transition to the larger, more globose cells of the cortex. Note that the cells of the cortex are filled with starch. Make a DRAWING of the skin and cortex of the healthy potato. Cut thin cross-sections (or use prepared slides) through sori of different ages; young and medium old. Put the sections from each into different watch-glasses. Mount the thinnest sections from the very young sori and NOTE :— 26. Whether the hypodermis and epidermis are affected; the cells where the plasmodium enters are killed. 27. The granular mass between and within the cells,—the plasmodium of the parasite. 28. Any discoloration of the cells. Is there any enlargement of the cells?’ Note the starch-granules. Iodine solution will stain the starch-grains and make them more evident. Examine the sections through the medium-aged sori. OBSERVE:— 29. The hypertrophy of certain of the cells; enlarged in which direction? These are called giant-cells. Is the plasmodium of the patho- gene to be detected in any of them? MHas spore-formation begun? 30. That some of these giant-cells are divided by cross-walls into several smaller cells; hypoplasia occurs as well as hypertrophy. 31. That this overgrowth of the cortical cells pushes up and eventually bursts through the skin. 32. Any effect of the pathogene upon the starch. 33. Effect on the nuclei of the host-cell. _ 34. Evidences of cambial activity in the uninvaded tissues beneath the sorus. Make a DRAWING Of a section through a sorus showing the histological conditions just prior to spore-formation. REPORT 1. Give the methods of control to be employed against this disease and explain the philosophy of their use. 2. Consult the literature on club-root of crucifers and write a brief description of the life-history of Plasmodiophora Brassicae Wor. comparing and contrasting it with that of Spongospora subterranea (Wallr.) Johnson. CLUB-ROOT OF CRUCIFERS This is the best known of the slime-mold diseases of plants. It is a distinctly metaplastic disease, causing a marked overgrowth of the affected organs. It is widely prevalent both in the Old and in the New World. It affects most of the common cruciferous crops, especially cabbage, cauliflower and turnips. SYMPTOMS The roots are the only organs of the host that show lesions. The specimens provided exhibit the symptoms at different stages in the develop- ment of the disease and on different hosts. (See illustration specimens of the disease on various hosts.) Examine carefully the specimens pro- vided and OBSERVE :-— 1. The relatively small size and the much more fibrous and branched character of the roots of the healthy plants as compared with the diseased roots. 2. The much swollen and enlarged roots of the diseased plants; occasional healthy roots arising from the stems above the lesion. Why? Determine by diameter measurements how many times the diseased roots have been enlarged. Roots enlarged in this manner are said to be hyper- trophied. 3. That the hypertrophy occurs either in the region of the root next to the stem or out in the feeding-roots. 4. That the hypertrophy involves the root in its entire diameter. It is not simply an outgrowth on the side of the root. 5. The specimens of club-root on the different hosts in the illus- tration jars. (See also Vermont Bul. 185, pl. II-V.) Determine whether there is any uniformity in the shape of the swellings which may be regarded as characteristic of this disease. 6. That the surface of the hypertrophied roots, especially in the old specimens, is much cracked and checked; to what due? These cracks allow the entrance of decay-producing fungi and bacteria. The succulent tissues quickly become soft and rotten and have a foul odor. The club-root pathogene itself does not cause the tissues to soften. 7. That the root beyond the hypertrophy, the branches and fine feeders, seem to be normal and healthy. 8. The abruptness with which the hypertrophy ceases at the base of the stem; this is a disease of the roots. Nodules, tubercles and galls due to other causes are often produced on roots of plants, as for example: the nematode-gall caused by minute worms; legume-tubercles and crown-gall of trees caused by pathogenic bacteria. (See illustration specimens in jars.) Make a DRAWING Of a ‘‘clubbed”’ root along side of a healthy one. Main- tain relative proportions. Where the roots are badly clubbed, the plants fail to head, or form loose worthless heads. Affected plants often wilt or “‘flag’’ during the heat of the day but recover at night. These symptoms exhibited by the tops can be well observed only in the field. 166 167 ETIOLOGY This disease is caused by the myxomycete, Plasmodiophora Brassicae Woronin. It is apparently an obligate parasite, saprogenesis being merely a period of rest. It has never been cultured saprophytically. Life-history. This pathogene has, normally, an annual life-history but its spores may evidently lie dormant in the soil for several years in the absence of a cruciferous crop. The Primary Cycle is initiated by spores that have Pomme’ dormant in the soil from a former season. Pathogenesis. When the affected roots rot, the spores of the patho- gene, mixed with the decayed host-tissue, remain in the soil. Selecting a root in an advanced stage of the disease, remove a bit and crush it in a drop of water on a slide; cover and examine with the high-power. oB- SERVE :-— 9. The minute globose hyaline spores, abundant among the crushed tissue-fragments. DRAW. These spores germinate in the spring after the manner of those of the saprophytic slime-molds. The spore-wall cracks and the naked protoplast creeps out. Study the process as illustrated in Vermont Bul. 175, fig. 6. copy to show several stages in spore-germination and the development of the swarmspore or myxameba. These myxamebae, thus set free in the soil water, come in contact with nearby roots of susceptible plants and infection results. The single uninucleated swarmspore enters through a root-hair. Here by rapid nuclear division and growth, a multinucleate ameba or plasmodium is formed which penetrates into the cortical tissues. By direct migration through the cell-walls and by the division of the meristematic host-cells into which the ameba have penetrated, invasion of the various tissues 1s effected. The plasmodium increases in size, destroys the protoplast of the cells in which it is lodged, and gradually fills the lumena of the cells. Make thin sections (or use prepared slides) through roots in the early stages of the disease. OBSERVE :— 10. The finely and densely granular multinucleate protoplasm of the pathogene in certain of the enlarged cortical or medullary ray-cells. Compare with the protoplasm of uninvaded cells nearby. (See Vermont Bul. 175, fig. 3-4.) DRAW an uninvaded and a normal host-cell, with contents, to show contrast. These multinucleate plasmodia, when mature, divide into spores, each one-celled. Cut sections (or use prepared slides) of diseased roots con- taining mature spores. OBSERVE :— 11. That the infested cells are packed with spores; uniform size of spores; and absence of capillitium, characteristic of most saprophytic slime-molds. The host-cell serves as a sporangium. DRAW an invaded cell with spores. 12. In which tissues of the root the pathogene is most abundant. Saprogenesis. The affected tissues gradually decay and the mature spores go into a resting- or dormant-period. No saprophytic activities, between spore-germination and infection by myxamebae in the spring, are known to take place. Secondary Cycles. It is known that the spores will germinate at once or very shortly after they are formed. ‘Therefore, if set free by the 168 early decay of affected tissues, they may cause secondary infections on roots of the same or later-planted hosts throughout the season. That this commonly happens appears certain. The phenomena are the same as those of the primary cycle. Pathological Histology. Make freehand sections of a small healthy root (or use prepared slides). With low-power, OBSERVE :— 13. The core of the root, made up of alternating wedges of xylem (vessels and wood-cells) and medullary rays. Note that the xylem- wedges are frequently fused toward the center of the stele so that the medul- lary rays are seldom continuous from the cortex to the center. Stain the section with a solution of iodine and NOTE :— 14. The yellow color taken on by the walls of the wood-cells which, with their thicker walls, are now more sharply contrasted with the medullary ray-cells. 15. The bark of the root surrounding the xylem-cylinder con- sisting in large part of the thin-walled cortex-tissues. 16. The groups of thick-walled sclerenchyma-cells in the outer cortex, stained deep yellow by the iodine. What is their function? 17. The ends of the phloem-strands, made up of small thin- walled cells in the inner cortex, each opposite a xylem-wedge. 18. The outermost tissues of the root, rough and torn,—the cork-layer. Make a diagrammatic DRAWING three inches in diameter showing the anatomy of a healthy cabbage root as seen in cross-section. Make an enlarged and detailed DRAWING of a V-shaped portion of the cross-section showing form and arrangement of cells from center to circumference. Include (in outline) at least one vascular wedge. Cut, mount and study a thin cross-section of a diseased root (or use prepared slide). OBSERVE :— 19. The abnormally increased diameter of the root. To what does this seem to be due; increase in size (hypertrophy) or numbers (hyperplasia) of the cells or both? (Compare with the section of the healthy root.) 20. The xylem-vessels in a few small groups. Note their isola- tion. To what part of the section are they chiefly confined? Why? (Compare Vermont Bul. 175, fig. 3.) 21. The ends of the phloem-strands composed of small regular cells arranged in rows around the outer end of the xylem-wedge. The relatively large amount of phloem, as compared with the amount of xylem; as compared with the amount of phloem in a bundle in the healthy tissue. 22. The abnormally broad medullary rays, resulting from the increased size of the cells. The dark masses in some of the cells,—the plasmodia or spore-masses of the parasite. 23. The cortex; the most abnormally increased of all the tissues. The cells are enlarged and perhaps increased in number. Some of them are filled with the brown masses of the parasite. Most of them show nucleus and cytoplasm. Note the entire absence of sclerenchyma or stone-cells; why wanting? 24. The layer of cork-cells on the outside. Are they affected? Make a diagrammatic DRAWING showing the anatomy of the diseased root as seen in cross-section. 169 Make an enlarged and detailed DRAwING of a V-shaped portion of the section from the center to the outside, including one vascular wedge and medullary ray. Indicate the presence of the parasite in the cells by fine stipple-work. | REPORT 1. Describe fully the effect of the disease on the morphology of the root. What is meant by pathological morphology? 2. Explain the difficulties involved in the control of this disease by eradication measures. LEGUME TUBERCLES The bacterial tubercles which commonly occur on the roots of legumes are not generally regarded as evidence ofa diseased condition. They are nevertheless pathologic in character. That the plant usually profits from their presence on its roots is no argument against their pathologic nature. The roots of all the common leguminous crops usually show these galls. SYMPTOMS Roots of various leguminous plants have been provided. (See also the illustration specimens in jars.) Study and compare the tubercles on the different hosts. OBSERVE :— 1. The shape, size and color of the galls; more or less characteris- tic for different hosts. 2. Location on the root-system; deep or shallow; on small or large roots; lateral or terminal? 3. Types of galls; simple and compound (branched). Make DRAWINGS of the tubercles on pea, bean, clover and alfalfa. ETIOLOGY The cause of these tubercles is a bacterial pathogene, Bacterium leguminosarum (Frank) E. F. Smith. It is probable that this species includes a number of more or less distinct biologic forms. Life-history. This pathogene is a highly specialized parasite, develop- ing normally in living plant-tissues which it stimulates to overgrowth. The galls which it induces are usually annual growths. It is probable that in most cases only primary cycles occur. The Primary Cycles are initiated in the spring and summer on the developing rootlets of the host. Pathogenesis. Active individuals in the soil-water constitute the inoculum. Study a mount from an actively growing pure culture provided. OBSERVE :— 4. The form and size of the bacteria. They are actively motile, having one polar flagellum (which can be seen only in specially stained preparations). These bacteria in the soil accumulate in small groups on the sides of the root-hairs. By means of some secretion, they gradually soften the wall of the root-hair and penetrate it. The root-hair is stimulated to bend or curl about the mass of penetrating bacteria in a characteristic fashion. Study the prepared slides showing root-invasion. OBSERVE :— 5. The curled tip and the infection-thread extending through the length of the root-hair. DRAW. 6. Under the demonstration microscope an infection-thread within the tissue of the root. Note the funnel-like swellings produced just before the host-walls are penetrated. DRAW. These bacteria, having penetrated to meristematic cells, multiply rapidly and stimulate abnormal cell-division, resulting in the formation of the gall. 176 171 Cut thin sections of tubercles. Examine the central bacterioidal region with the high-power. OBSERVE :— 7. The numerous infection-threads extending from cell to cell. This shows how new cells, formed by the primordial meristem, are infected from the adjoining bacteria-filled cells. 8. The immense number of bacterioids in each invaded cell. 9. That they are for the most part not rod-shaped like the indi- viduals in the soil, but are club-shaped to Y-shaped; most evident in the central cells. As the organisms in the host-cells or in old cultures cease to divide, they gradually take on these so-called involution-forms. (See Virginia Ann. rept. 1909—1910:136—137.) Some of the individualsin the outer cells of the bacterioidal tissue remain active and rod-shaped. The degenerate bacterioids are attacked by the enzymes of the host, and the nitrogen stored within them is made available for the growth and development of the host. Saprogenesis. With the death and disintegration of the tubercle- tissues at flowering-time of the host, the active rod-shaped bacteria in the gall are set free in the soil. Whether during their sojourn in the soil, they lead an active saprophytic existence, though highly probable, is not certain. They can be readily grown on artificial media. They are not known to produce spores. Pathological Histology. Longitudinal sections of tubercles and normal root-branches are provided. Examine and OBSERVE :— 10. The general shape and appearance of the longitudinal section of the tubercle. Compare with that of the young lateral root. 11. The kind of tissues from which the tubercles and the roots respectively arise. 12. The vascular strands. Note their condition at the base of the bacterioidal region and the arrangement of the xylem and phloem. Compare with the condition in the young lateral root. 18. The primordial meristem and root-cap. Are they present both in the tubercle and in the lateral root? 14. The cortex. Is it continuous with that in the root? 15. The epidermis. Is it present in the tubercle as well as in the lateral root? 16. The bacterioidal region. Where is it located in the tubercle? Note the size and contents of the cells. Note the outer cell-layer limiting the bacterioidal region,—the starch-sheath. What metaplastic conditions predominate in the tubercle, hypertrophy or hyperplasia? _ Make a diagrammatic DRAWING of a longitudinal section of a root- tubercle; similar comparative DRAWING of the lateral root. In these drawings only an outline need be made to indicate the comparative shape of the lateral root and the tubercle, and to locate the various tissues men- tioned above. Examine the prepared cross-sections of the tubercles. OBSERVE :— 17. The bacterioidal region, ring of bundles, cortex and starch- sheath. DRAW. 172 18. The effect of the bacterial invasion on the organs of the infected cells; nucleus, cytoplasm and walls, as compared with those of a homologous healthy cell. (Read Fred, Virginia Ann. rept. 1909—1910:123, first paragraph.) Detail in enlarged DRAWwINGs a healthy and an infected cell showing the cell-organs and contents. REPORT 1. Present the evidence to show the pathological nature of the legume tubercles. Read in this connection: Smith, E. F. Bacteria in relation to plant diseases 2:97-146. 1911. Fred, E.B. The infection of root-hairs by means of Bacillus radicicola. Virginia Agr. Exp. Sta. Ann. rept. 1909-1910:123-137; and other references given in the text. PEACH LEAF-CURL This is a common and frequently destructive disease of peaches in nearly every peach-growing section. It is especially severe in regions subject to cold, wet weather in the spring. One of the most profitable commercial varieties, the Elberta, is particularly susceptible. SYMPTOMS ‘ It is chiefly a disease of the leaves, although the current season’s shoots may also suffer. Shoot-infection is especially serious when nursery-stock is affected. Flowers and fruit rarely show lesions of the disease. On the leaves. Examine the material provided. OBSERVE :— 1. The flexible character of the normal portions of the leaf. Tear it and note the texture. 2. The wrinkled and distorted portion of the leaf affected by the curl. Tear and compare with the healthy portion as to texture and flexibility. Explain the difference. Compare with the healthy portion as to color and thickness. 3. The character of the distortion. In which direction as re- gards the long axis is the diseased leaf wrinkled? Why? DRAw. Examine photographs and Cornell Bul. 276, fig. 83-86. OBSERVE :— 4. That the diseased leaves soon drop, partially or wholly defoliating the tree. Later new leaves are usually put forth. On the twigs. Study the specimens provided. OBSERVE:— 5. The dwarfing of the shoot due to a shortening of the inter- nodes, giving it a rosette-like appearance. 6. The much thickened fleshy stem,—hypertrophied; more or less definite linear ridges often extending down on the previous years growth. 7. The badly infected leaves. The leaves on diseased twigs are more severely affected than on the healthy twigs, for invasion becomes general or systemic and the leaf-fundaments become diseased as they are formed. Most of the affected shoots gradually die. (Compare U. 5. Agr. Dept., Veg. Phys. and Path. Div. Bul. 20, pl. V.) On flowers and fruit. If specimens or photographs are available, study the character of the lesions on these organs. DRAW. The curl on the leaves affects the fruit indirectly by preventing setting or by causing it to fall. (Study U. S. Agr. Dept., Veg. Phys. and Path. Div. Bul. 20, pl. XVII, and table 33, p. 124.) ETIOLOGY The cause of this curl is Exoascus deformans (Berkley) Fuckel, one of the primitive ascomycetes of the order Protodiscales. No definite fruit-body is formed, the asci developing directly from the mycelium in an exposed hymenium over the surface of the lesion. Life-history. Relatively little is positively known about the life- history of E. deformans. Opinions with respect to the life-habits of this pathogene are based very largely upon circumstantial evidence. No true asexual stage of the fungus is known. 173 174 The Primary Cycles are initiated in the early spring when the buds swell and begin to open, by inoculum which has overwintered on the hairy bud-scales. Presumably this inoculum is some kind of spores; just what kind and how they reach the bud-scales is not known. Pathogenesis. Examine the buds on the peach twigs provided. OBSERVE :— 8. The hairy character of the outer bud-scales. Remove one and study it under low-power. Minute globose spores may sometimes be detected, lodged among the long hairs on the scale. These may belong to the leaf-curl pathogene, at least present evidence warrants the belief that such spores lodged in this way serve as the primary inoculum. Make an enlarged diagrammatic SKETCH of an infested bud. The spring rains which cause the buds to swell and to open, also cause the spores to germinate and send forth a slender germtube which enters the bud between the scales and penetrates the tender leaves. As the leaves develop, the mycelium within spreads between the cells and stimulates the growing tissue, resulting in a curling and fluting of the blade. The germtube may also penetrate into the growing tissues of the developing twig. Make thin sections through diseased leaves or twigs; clear in chloral hydrate; wash and stain for some time in eosin or methyl blue; wash and mount in water. LOCATE :— 9. The intercellular mycelium, fitting tightly in, and conforming with the intercellular spaces. No haustoria are formed. DRaAw a bit of the mycelium with adjoining host-cells. Branches of this mycelium pass toward the surface between the epider- mal cells. Make thin tangential sections from the surface of the diseased leaf. Stain as above and study under the high-power. MAKE OUT:— 10. The very abundant subcuticular mycelium; its irregular septate form; its branching and anastomosing habit. From this mycelium arise the asci. DRAW. Study cross-sections (freehand or prepared) of a leaf through a lesion bearing asci. OBSERVE :— 11. The row of enlarged and angular epidermal cells of the host; their organs and contents. . 12. The layer of long, more or less angular asci, containing spores, standing at right angles on the epidermal cells. In the prepared slides, OBSERVE :— 13. Some of the asci, small and young with deeply stained protoplasmic contents and nuclei. 14. Mature asci containing deeply stained ascospores or empty; shape and size of the spores; number in an ascus. DRAW a portion of the epidermis showing asci, old and young, in dif- ferent stages of development. 15. That these ascospores often increase in number within the ascus by budding like yeast (known by the large number of small spores which the asci contain). DRAW. Saprogenesis. The ascospores when mature are shot through a rupture in the top of the ascus. Their further history is unknown. The mycelium in a lesion produces but one crop of ascospores and then ap- parently dies with the leaf which soon falls to the ground. ‘There is prob- ably some saprogenic activity on the part of this pathogene between the 175 dissemination of the ascospore in early summer and primary infection the following spring, but of this nothing is known. Secondary Cycles may or may not occur. This point is not deter- mined. The ascospores germinate in water by budding or by the pro- trusion of a short germtube when placed on leaves of the host. Artificial inoculation of the host has never resulted in infection. (Read U.S. Agr. Dep., Veg. Phys. and Path. Div. Bul. 20, bottom of 38 to 40.) copy figures from pl. IV, showing two types of spore-germination. Pathological Histology. Study the prepared cross-sections of a dis- eased leaf. Select a place in the section where the diseased tissues may be compared with the normal. OBSERVE:— 16. The increased thickness of the leaf in the diseased portion. To what is this due, increase in size, or number of cells (hypertrophy or hyperplasia) ? 17. Which tissues are most affected, palisade or spongy paren- chyma? 18. The affect on the number, shape and arrangement of the palisade-cells; chloroplastids and cell-walls (hypoplasia and metaplasia). These cells were attacked before they began to differentiate into palisade- cells. 19. The effect on the epidermal cells on the upper surface of the leaf; on the lower surface. Make a detailed pRawinG showing comparatively the histological structure of the diseased and the normal portions of the leaf. REPORT 1. Write a letter to a peach-grower, giving brief and current directions for controlling peach leaf-curl. LEAF-BLISTER OF OAKS This is a very common leaf-disease of oaks. Frequent epiphytotics, with more or less serious effects on the host, occur in the southern portion of the United States, while in the north very little damage is done. SYMPTOMS The leaves only are affected. In the dry material, NoTE:— 1. The blisters; more or less circular; varying greatly in size. 2. That in some cases the spots have become confluent and the entire leaf is much curled. 3. That the blister is usually convex on the upper surface of the leaf and concave on the lower; however, this is not a constant character. 4. That the upper or convex surface of the blister is, in young spots, lighter green than the normal leaf-tissue but, that in the older spots, it becomes more or less flecked with brown areas. 5. That the lower or concave surface of the blister is a bluish gray in the fresh condition but changes on drying to a dirty or brownish gray. The coloration and velvety appearance of the under surface is due to the fruiting stage of the causal fungus. Make a SKETCH to show the symptoms of leaf-blister. ETIOLOGY The pathogene causing the leaf-blister of oaks is Taphrina coerulescens (Desmazieres and Montagne) Tulasne, an ascomycetous fungus belonging to the order Protodiscales. No fruit-body is formed by these primitive ascomycetes. The asci are developed directly from the mycelium in a hymenium on the surface of the host. The peach leaf-curl pathogene, Exoascus deformans (Berkley) Fuckel, is closely related to T. coerulescens (Desm. and Mont.) Tul. Life-history. As is the case with the peach leaf-curl fungus, the life- history of T. coerulescens is imperfectly known. Ascospores, borne on the blisters in the spring and summer, bud in the asci and form numerous secondary spores. These spores are supposed to hibernate in some way and initiate primary infections the following spring. The Primary Cycles are initiated in the early spring by the over- wintered inoculum (kind unknown). Pathogenesis. The pathogenic activities of this fungus are exhib- ited entirely by the sexual or ascigerous stage. In fact no true conidial form of this pathogene or, for that matter, of any of the entire order, the Protodiscales, to which it belongs, is known. Examine the stained cross-sections of a blister and NOTE :— 6. The mycelium. To what portion of the leaf is it confined? 7. The layer of more or less angular asci standing at right angles to the lower epidermal cells. 8. The wedge-shaped root-like projections pushed down between the lower epidermal cells and which serve as hold-fasts for the asci. 9. The spores within the asci. They are small and either eight in number or numerous (probably in some cases as many as a hundred). Some authors have suggested that the budding of the eight ascospores, 176 Lae which results in these numerous asexual spores without a mycelial stage intervening, constitutes in reality asexual reproduction, and that these spores are conidia. This is largely theoretical, however, to account some- how for a conidial stage. DRAW a portion of the lower epidermis as seen in prepared cross-sections showing mycelium, holdfasts, and young and old asci with spores. Saprogenesis. The whereabouts and activities of this pathogene during saprogenesis, if such a period ensues, is unknown. Pathological Histology. Although the mycelium of TJ. coerulescens is confined to the space it makes for itself between the lower epidermal cells and the cuticle, the effect of the parasite is seen throughout the thick- ness of the leaf. In the stained cross-sections, find and compare the healthy with the diseased part of the leaf. NOTE:— 10. The hypertrophy in the lower epidermis, spongy mesophyl, palisade-mesophyl and upper epidermis. 11. The hyperplasia in the lower epidermis and spongy mesophyl- tissues. 12. That in the normal tissue the cells of the lower epidermis are longer than broad. The effect of the fungus is to cause these cells to increase greatly in size and, being so tightly packed together, they elongate in a direction perpendicular to the surface of the leaf. Finally septa may be laid down at right angles to their long axes. 13. That the cells of the spongy mesophyl are increased both in number and size and are tightly packed together, largely eliminating the intercellular spaces so common in the healthy tissue. 14. That the cells of the palisade-mesophyl are longer and wider than the normal. 15. That the cells of the upper epidermis are somewhat larger and more globose than the normal. 16. That the chloroplastids in the diseased cells are much smaller and fewer in number. Make DRAWINGS showing (comparatively) the histological structure of the diseased and normal portions of the oak leaf. Preserve correct proportions between the two drawings. REPORT 1. From the literature on leaf-blister of oaks and the methods used for control of peach leaf-curl, suggest possible measures of control for leaf-blister. BLACK KNOT OF PLUMS AND CHERRIES This is one of the most striking diseases of stone-fruits. It is an indi- genous disease peculiar to our native wild species of plums and cherries and is frequently destructive to our cultivated forms, especially certain varieties of plums and sour cherries. The disease is not known to occur outside of North America. SYMPTOMS The disease affects only the woody parts of the host, usually only the twigs, though it may extend from spurs to the larger limbs or body of the tree. (See illustration specimen.) Two seasons are required for the full development of the knot . Study the material provided showing the character of the knots in the spring of the first season. OBSERVE :— 1. The relation of the knot to the twig. Is the entire circum- ference involved? 2. The shape and color of the gall. 3. The relation of the swollen tissues to the epidermis and cork- layer of the healthy part. 4. The character of the surface of the knot. The olivaceous lumps or patches scattered over the brown woody surface. These are the conidial stromata. These stromata bear mature conidia in the spring. Compare several specimens on the above points. SKETCH a typical knot. The galls are probably initiated at buds or short spurs. Study the very young galls provided and OBSERVE :— 5. The unruptured swellings on the side of the spur or in the twig nearby. What does this indicate as to the infection-court? DRAW. Study some of the specimens showing the character of the galls the second season. OBSERVE :— 6. The darker color and more hard and woody character of the galls. 7. The continuous black perithecial stroma covering the exposed surface of the gall. 8. The minute pimple-like perithecia arising from, and crowded over the surface of the stroma. 9. Secondary galls arising just above or below some of the primary ones; known by their lighter color and conidial stromata. DRAW to show the character of secondary galls and secondary gall- formation. 10. That affected twigs may be bent at right angles to the knotted side. DRAW. ETIOLOGY The black knot is caused by the ascomycetous fungus, Plowrtghtra morbosa (Schweinitz) Saccardo. Life-history. This pathogene presents in its life-history one striking variation from the usual type; it requires two years to complete a life-cycle. The Primary Cycles are initiated in the early spring by inoculum produced on two-year-old knots. 178 17 Pathogenesis. The ascospores constitute the inoculum for the primary cycles. With the scalpel remove a few of the mature perithecia and crush in a drop of water or potassium hydroxide on a slide. Cover and OBSERVE :-— 11. The ascospores; their form, number in ascus, number of cells and color. DRAW. If living material is available, study the germinating ascospores. These ascospores mature and are discharged from the perithecia, usually during March. They are carried to the buds on the previous year’s growth and infect the twig. The development of the pathogene and the reaction of the host is slow. Slight swelling of the infected twig begin to show by autumn. It develops rapidly during the early days of the following spring and burst through the epidermis. On the exposed surface, the scattered conidial stromata develop on which conidiophores bearing conidia are matured in late spring or early summer. These conidia are dissemi- nated and initiate secondary cycles. Study cross-sections through the conidial stromata and OBSERVE :— 12. The structure of the stroma; relation to mycelium in host; size of cells; color. 13. The erect conidiophores; septate or non-septate‘ 14. The conidia; shape, size, color and number of cells; where and how attached to conidiophores? Make a DRAWING to show these structures. After the conidia are matured and disseminated, the velvety covering of conidiophores gradually disappears, giving place to the continuous black crust-like stroma of the sexual stage which has been developing, so that by autumn the knot shows the black carbonaceous character, distinctive of its second season, and the minute pimple-like perithecia (fruit-bodies of the sexual stage) developing on the surface. During the first warm days of the spring (two years after primary infection) ascospores are formed within the asci in these perithecia. Examine with the hand-lens, the surface of mature galls provided. OBSERVE :— 15. The minute black bodies crowded together over the surface; shape and size; adherent to each other or separate on the stroma? . 16. The apex of the perithecia often depressed; a minute opening at the center of each,—the ostiolum. Study prepared sections through mature galls showing longitudinal sec- tions of perithecia. MAKE OUT:— 17. The relation of perithecia to each other and to the stroma; character of the stroma as compared with that of the conidial stage. _ 18. The structure of the perithecial wall; ostiolum; relation of asci and paraphyses to the perithecial cavity. Crush in water one of the mature perithecia. OBSERVE:— 19. The structure of the asci, ascospores and paraphyses. Make an enlarged prawinc of a longitudinal section of the peritheci1um and supporting stroma to show these structures in detail. The ascospores mature in early spring and are shot, during rainy periods, from the asci out of the ostiolum. Caught by the breeze, they are carried to the trees and infection occurs in the swelling buds or develop- ing shoots. Thus in two full years is the primary life-cycle, starting with ascospores, completed in the production of another crop of ascospores. 180 Saprogenesis. As the pathogene is continuously associated with its living host, it may be regarded as having no saprogenic phase in any of its life-cycles. However, as a matter of fact, there is often little living host-tissue in the galls during the period of the maturing of the ascospores. Secondary Cycles are initiated by the conidia, produced on the galls, during the next growing-season after that in which the primary infections were initiated. These secondary cycles require slightly less than two full years for their completion and, like the primary, end with the production of ascospores. ‘The pathogene structures, developed during the secondary cycles, and the host reactions are like those of the primary cycles. Mycelium spreading from the primary (or secondary) galls into adja- cent healthy tissues often give rise to secondary galls. This is regarded by some as secondary infection (Stewart, Amer. Jour. Bot. 1:114). Pathological Histology. The effect of this pathogene on the host is one of stimulated overgrowth of the invaded tissues. Cut with a knife or scal- pel (not a razor) across one of the galls provided for this purpose. ‘Trim the surface smooth and with hand-lens, MAKE OUT:— 20. The anatomical distortions that have occurred in the elements of the vascular cylinder and bark, comparing constantly with the struc- tures in the normal portion of the twig. Make a diagrammatic DRAWING of the entire cross-section showing normal and pathological anatomy. Label corresponding tissues in each. Study under the microscope the prepared sections through young one- year old galls. OBSERVE :— 21. The character of the host-tissue on which lies the stroma of the fungus; size, shape, contents of cells and tissue-relations. 22. The mycelium in the tissues; inter- or intracellular? 23. The mycelial strands and fans in some places; their pseudo- parenchymatous character. What is their relation to the stroma? 24. The depth toward the pith to which the pathological effects are evident. 25. The broadening of the rays in the diseased region; due to hyperplasia or hypertrophy? 26. The isolation of the cambium at the outer ends of the xylem- wedges; wanting in the abnormally broad rays. 27. The inhibition of xylem-elements and the abnormal develop- ment of parenchyma in the xylem-wedges. The enlargement of the gall the second year is largely due to a marked hypertrophy of these parenchy- mal cells. 28. The isolated groups of summer-wood vessels in the xylem- parenchyma just inside the cambium. 29. The isolated xylem-elements in the diseased bark. These result from the misplaced and broken segments of the cambium opposite the broad rays. 30. The proportional increase in thickness of bark and wood in the diseased region. The outer bark sluffs off before conidial formation. Make a full-page DRAWING, detailing cells in the different regions, to bring out the histological changes above emphasized. REPORT 1. Prepare a diagram showing the two types of life-cycles in Plowrightia morbosa (Schw.) Sacc. and their relation to each other. CORN SMUT This is the most common and most noticeable disease of corn. It is sometimes known as boil-smut to distinguish it from the head-smut. It affects all varieties of field-corn, pop-corn and sweet corn. Some varieties of sweet corn suffer severely from this smut. SYMPTOMS All parts of the plant above ground are subject to the disease. Unlike most of the cereal smuts, invasion is local. The lesions are characterized by marked hypertrophy. On the stalk. Study the specimen provided and OBSERVE :— 1. At what points on the stem the galls are usually located. 2. The large size of the boils and the comparatively small area from which they arise. Is there any evidence of injury to the adjacent host-tissues? 3. The texture of the boils. They are more firm in fresh speci- mens, especially when yet immature; the tough fleshy covering of such galls. 4. The color; compare old and young boils. 5. The dark dusty spore-mass filling the mature boils. A relatively large portion of the hypertrophy is composed of pathogene structures (mycelium or spores). Make a SKETCH to show stem-boils. On the leaves. Lesions are comparatively rare on the leaves. In the specimens provided, OBSERVE :— 6. The small boils arranged in rows parallel with the veins. Do they seem to arise from or between the veins: which side of the leaf? 7. Any effect on the tissues adjacent to the boils; opposite the boils. SKETCH leaf-lesions. On the ear. Affected ears are very common, especially those with exposed tips. In the specimens provided, OBSERVE :— 8. The form, size and location of the boils. 9. That they are each an enlarged kernel. Find kernels in different stages of hypertrophy. SKETCH a diseased ear to show healthy kernels and diseased ones, hypertrophied in various degrees. On the tassel. The boils of this smut are very common on tassels but may be confused with those of the head-smut. (See Kansas Bul. 62:199 and pl. VI, VIII—X.) In the specimens provided, OBSERVE :— 10. That the boils on the tassels are but hypertrophied parts of the flowers. 11. That only flowers here and there in the tassel are affected. 12. That the character and degree of malformation varies in different flowers. Carefully dissect a healthy and a diseased flower. Make a series of comparative DRAWINGS to show the effect of the disease on different organs of the male flower. 181 182 ETIOLOGY The pathogene causing corn smut is Ustilago Zeae (Beckmann) Unger, one of the Ustilaginaceae. It was first described as one of the puff-balls by Beckmann in 1768 and has been, since that time, a frequent subject for investigation by mycologists and phytopathologists. Life-history. It differs markedly in its life-habits from most of the com- mon cereal smut pathogenes. There are normally, in temperate climates at least, only the primary cycles. The Primary Cycles are initiated at any favorable time during the period of active growth of the host. Overwintered chlamydospores, usually in the manure on the field, are the sources of inoculum. Pathogenesis. Some of the chlamydospores from an old smut-boil have been germinated in manure-extract on the slides provided. Examine under the microscope and OBSERVE :— 13. The large globose spiny dark-brown chlamydospores. 14. From some of these, the protruding hyaline promycelium (basidium). 15. The crack in the epispore through which the promycelium is protruded. 16. The septa in the promycelium, from below each of which arise one to several slender pointed sporidia. They are often produced in great numbers; sometimes in chains. DRAW a germinating chlamydospore showing abundant sporidial production. These sporidia are carried by the wind to the growing corn. Some of them lodge on the growing tissues of the host near the joints within the leaf-sheath, the emerging silks, or the blossoms on the tassels. Here they germinate, sending out germtubes that penetrate these embry- onic tissues, and give rise to the mycelium. This mycelium does not spread through the tissues to any great distance from the point of infection; every boil probably arises from a separate infection. The hyphae grow in great masses into the hypertrophied tissues of the boil and form the greater bulk of the excrescence. Chlamydospores are soon developed in chains within short branches of this mycelium. The rest of the mycelium gelatinizes and disintegrates more or less. To study the mycelium in the host-tissue about the base of the boil, make thin longisections of the stalk, just beneath the boil. Stain with methyl blue or eosin. Examine and in the pith-tissues, OBSERVE :— 17. The slender hyphae in the intercellular spaces or penetrating the cells; often in strands of several hyphae or gnarled in the intercellular spaces. 18. Short knotted or irregularly swollen short branches sent into the cells,—the haustoria. DRAW to show the mycelium in the host-tissue. To study the distribution of the mycelium in the boil and the formation of the chlamydospores, examine prepared sections through a partly ma- tured boil. Make prawincs to show the structures studied. Saprogenesis. Mount some of the black spore-mass in potassium hydroxide. Study with the high-power and OBSERVE :— 19. The shape, size and color of the mature chlamydospores; the short spines which thickly beset the spore-wall. 183 20. Any variation in the spores as to size and shape. Look for bits of mycelium. Make an enlarged DRAWING of several of the spores. These chlamydospores go with the fodder into the manure and finally out on the land. They winter over in the manure and germinate during the following season. ‘Their dependence upon saprophytic nourish- ment in germination is evidenced by the fact that they develop sporidia much better in a nutrient solution, e.g. manure-extract, than they do in water. REPORT 1. Explain why seed treatments, so generally effective with smut diseases, will not control the corn smut. HOLLYHOCK RUST This is a rust disease peculiar to a number of malvaceous hosts. It is indigenous to Chili where it was discovered in 1852. It is especially destructive to the hollyhock and is now known as a common disease of this perennial in nearly every temperate country of the globe. SYMPTOMS The lesions of this disease occur on all the above-ground parts of the host, but are usually most numerous on the leaves. In severe cases, the calyx and seed-capsules are affected. On the leaves. Examine the specimens provided and OBSERVE :—~ 1. The cushion-like pustules scattered over the leaf-surface,— sori of the pathogene; most abundant on which side? 2. The variations in size and shape of the sori. 3. Color. This varies with the age of the lesion. The youngest lesions usually show a distinct bright-yellow color, especially on the upper surface or where they occur on the veins and petioles. A little later the fully developed sorus (telium) takes on a rusty brown color and is sur- rounded by a yellowish zone. When the spores of the telium begin to germinate, the color becomes a grayish brown. As the pustule dies it turns black. — 4. The thickened character of the leaf-tissue in well developed lesions; there is slight hypertrophy. 5. In old lesions, the dead and shriveled sorus surrounded by a narrow zone of necrotic leaf-tissue. This dead tissue sometimes falls out, leaving small round holes in the leaf-blade. DRAW a diseased leaf to show the characters of the lesions at various stages. Where the lesions are very numerous, the entire leaf-blade withers, turns brown and finally falls from the stem. The general effect of a severe infection is best observed in the field. On the stems and the petioles. Examine the specimens provided. OBSERVE :— 6. The shape and size of the pustules; usually larger than those on the leaves. Why? 7. The elongated dead zone about the older lesions. How deep does the lesion extend? The lesions are very limited. They frequently dry out and disappear except for a large oval scar left by the healed wound. DRAW several stem-lesions. On the fruit. Study the lesions on the flowers provided (best studied on the fruits of Malva rotundifolia L). OBSERVE :— 8. The lesions on the calyx; compare with those on leaves and stems. 9. The sori on the seed-carpels; color, size and location. DRAW. The pathogene is often distributed on seed infested in this manner. ETIOLOGY The hollyhock rust is caused by a uredinaceous fungus, Puccima Malvacearum Montagne. 184 185 Life-history. It is a so-called lepto-form or Leptopuccinia, i.e. it has neither aecia nor uredinia, producing only telia. The teliospores usually germinate 7 situ, as soon as mature, to form promycelia with sporidia. The Primary Cycles occur on the first leaves developed from the perennial root in the spring. The sources of inoculum are the old dead leaves, diseased the previous season, or overwintered living leaves in which the pathogene has hibernated. Pathogenesis. The inoculum consists of the sporidia. These are formed on the promycelium which develops from the teliospore. Teliospores which are produced late in the autumn often do not germinate at once but remain dormant on the old dead leaves. More commonly, however, late infections on immature green leaves of the hollyhock or on those of Malva rotundzfolia do not develop telia until early spring. The teliospores in these telia germinate and sporidia for the primary infections are formed. Study germinating teliospores; or illustrations in Phytopath. 1, pl. XIII. OBSERVE :— 10. The long slender basidium (promycelium), most commonly developed first from the apical cell. 11. The densely granular protoplasm of the apical portion of the basidjum; its final division into four cells, and the formation of a sporidium from each. 12. That sometimes the four apical cells separate before sporidia are developed. Make a series of DRAWINGS to show sporidial formation. The sporidia are carried by the wind or splashing rain to the leaves nearby. Here they quickly germinate sending forth a short germtube which penetrates the host. DRAW several germinating sporidia. These sporidia are uninuculeate and develop within the host-tissues a septate uninucleate mycelium. Study thin sections (freehand or prepared) through a lesion. OBSERVE:— 13. The slender, often matted, septate mycelium in the inter- cellular spaces or forcing the host-cells apart. Are haustoria formed? 14. The matted mycelial stroma from which arise the slender teliospore-stalks, forming the telial sorus. 15. The teliospores; form, size, color, septation and thickness of walls. 16. Young spores in various stages of development. Make a detailed DRAWING of a telial sorus in section with adjacent host-tissue and intercellular mycelium. The teliospores germinate in situ, giving rise to the sporidia which, scattered by wind or rain, initiate secondary cycles. Secondary Cycles are initiated repeatedly throughout the season and conform in their development to that of the primary cycles except that in the case of late secondary cycles, teliospores, which have developed, may fail to germinate at once and overwinter on dead leaves and stems. Very late secondary cycles on overwintered living leaves may fail to develop telia until the following spring. 186 Pathological Histology. Make a comparative study of diseased and healthy areas in prepared cross-sections of the leaf. DETERMINE :— 17. What pathologic changes, if any, in number, form and size of cells has resulted from the presence of the pathogene. 18. What changes have taken place in the protoplasts of affected cells; nucleus, cytoplasm and chloroplasts. Make DRAWINGS of diseased and healthy tissues to show the pathologic effects. REPORT 1. Detai! a plan for controlling the hollyhock rust in border- plantings. Give satisfactory reasons for each step in the procedure. RUST OF CEDAR AND APPLE This is a very common disease of the apple in many sections of the country where the red cedar grows. It is especially prevalent in the Mis- sissippi Valley, northeastern New York, New England, Virginia, West Virginia and other southern states. The effect of the pathogene on both hosts is very marked. Most of the rust diseases of rosaceous plants are harbored by some species of cedar during the winter. In the case of the rust here con- sidered, the pathogene overwinters on the red cedar, Juniperus virginiana L. The summer form of the pathogene occurs on wild crab, Pyrus coronaria L., as well as on the cultivated apple. The rusts appearing on pear, quince and hawthorne are usually caused by species distinct from that causing the apple rust; all, however, are closely related. SYMPTOMS The symptoms differ strikingly on the two hosts. On the apple. The material provided was collected in midsummer. Examine the affected leaves and OBSERVE :— 1. That the pathogene -produces a leaf-spot. How does it differ from other leaf-spots? 2. The differences in the character of the spot on the upper and lower surfaces as to color and definiteness of outline. 3. The presence of black pimple-like structures on the upper surface,—the pycnia (spermagonia) of the pathogene, probably function- less male structures. 4. The groups of brownish, somewhat cylindrical or fimbriate structures on the lower surface,—fruit-bodies called aecia (aecidia). SKETCH to show the above characters. The general effect of the pathogene is to give the trees a striking yel- lowish color in contrast to the dark green of the healthy trees nearby. Early defoliation follows severe infections. There is a marked variation in the susceptibility of varieties. Wealthy and Jonathan are especially susceptible. Lesions appear on the fruit when it is about one-fifth grown. They resemble those on the foliage. Examine diseased fruits provided and OBSERVE :— 5. The color and location of the diseased area. 6. The dwarfing effect on the fruit. Recall the effect on the leaf. 7. The kinds of pathogene-structures developed in these lesions. DRAW a diseased fruit. On the red cedar. The material provided was collected in early-spring (April). OBSERVE :— 8. The large brown galls. Form, size, consistency, and surface characters. 9. The’ spore-cushions scattered over the surface,—the telia (teleuto-sori). 10. The attachment and the relation of the gall to the twig. Each gall results from an enlargement of a single leaf, according to certain authors or of the stem in the axil of the leaf, according to others. 187 188 Remove one of the healthy leaves and NoTE :— 11. The size, form and relation to the twig. SKETCH a normal leaf and a diseased or galled leaf; maintain proper proportions. The most striking sign of this disease on the red cedar is exhibited during warm spring rains in April and May. From the telia scattered over the gall, long yellow gelatinous teliospore-masses protrude, giving the effect, from a distance, of large yellow fruits; whence the popular names cedar- apples and cedar-flowers. ETIOLOGY This disease is caused by one of the Uredinales, Gymnosporangium Junipert-virginianae Schweinitz. As already noted, the pycnial stage (O) and the aecial stage (I) occur on the leaves and fruits of the cultivated apple and wild crab. The telial stage (III) is found on the red cedar. A uredinial stage (II) is wanting. Life-history. The apple rust-fungus continues in close association with the living tissues of its hosts throughout its entire life-history. Primary Cycle Pathogensis. The inoculum for the primary cycle consists of sporidia which are produced on the red cedar. They are developed on a promycelium which in turn arises from a teliospore. Moisture of six or more hours duration is necessary for sporidial formation. As soon as the humidity decreases sufficiently to cause appreciable evaporation, the sporidia are forcibly ejected. This occurs from April to June. Sporidia are carried to the apple by the wind. Germination follows within a short time in the presence of moisture. Two types of germina- tion occur; one in which germtubes develop directly from the sporidia, and the other in which secondary sporidia are formed on a short germtube. The latter type is more common. (See Phvtopath. 3:282, fig. 1, and Ne- braska Rept. 22, pl. III, fig. 5; or Virginia Tech. bul. 9, fig. 9.) copy to show types of sporidial germination. The germtube arising from the secondary sporidium penetrates the cuticle. In the case of the leaf, this occurs on the upper surface. The mycelium developed from the sporidial germtube ramifies through a limited area of the leaf, with the result that tissue-changes are effected and certain fruit-bodies (O and I) are developed. Examine the apple leaves again, using hand-lens. OBSERVE:— 12. The pycnia on the upper surface of the leaf; their form and distribution. 18. The aecia on the lower surface of the leaf; their form, distribution and size. The long exerted peridium (aecial-wall),—a promi- nent character of aecia of this fungus. Rust-fungi showing aecia with such peridia belong to the form-genus, Roestelia. Accordingly the apple rust-fungus was formerly called Roestelia Pyrata (Schw.) Thaxter. Make enlarged DRAwINGs to show the pycnia and aecia as they appear under the hand-lens. Mount in potassium hydroxide some of the peridial cells and aeciospores from the aecium. Study and praw to distinguish them. Examine prepared slides showing sections through lesions on an apple leaf. OBSERVE :— 14. The abnormal tissue-developments. Which tissues are involved? How affected? 189 15. The pyenia; their form and contents. 16. The aecia; their position with reference to the pycnia, the relative size of the two structures; their form, structure and contents. Make a DRAWING to show the points observed in 14, 15 and 16. (See Virginia Tech. bul. 9, fig. 13.) The pycnial stage always precedes the aecial stage in the development of those rust-fungi possessing these spore-forms. Aeciospores never re- infect the apple. Secondary Cycles Pathogenesis. The inoculum for the secondary cycles consists of aeciospores which are discharged from July first to the end of the grow- ing-season. They are blown to the red cedar and there initiate the cedar- apples. The aeciospores apparently must undergo a period of rest before germination. The question of whether infection occurs in the fall or spring is yet unsettled. The way in which the germtube gets into the cedar isnot known. The manner of germination is not essentially different from that of other fungous spores. A simple germtube is formed; this on entrance into the host-tissue develops into a mycelium which stimulates the growing cells, and a gall results. This becomes evident the following June. Study the young green galls provided. These increase in size during the summer and become brown and full sized by winter. The fungus passes the second winter of its life-history as mycelium in the full- sized gall. From the gall provided, remove a small bit of tissue to a drop of water on a slide and crush. OBSERVE :— 17. The hyphal threads throughout the mount. The character of the host-cells. Examine prepared sections through mature galls. NOTE:— 18. That the gall shows cortex and vascular elements. 19. The mycelium of the fungus and its relation to the host-cells. Are haustoria present? In early spring the mycelium forms, at certain places beneath the cortex, stromata from which are developed the telial horns. Examine galls showing these horns. NOTE:— 20. That the horns arise from galls as described. 21. The depression at the base of each horn. 22. The color, size and shape of the horns. What is their con- sistency when dry; when wet? On the end of each long stalk-cell (sporophore) a teliospore is devel- oped. These are matured by March and April. Germination of the teliospore results in the formation of a promycelium which bears sporidia. Make a mount of teliospores from the horns provided. OBSERVE :— 23. The size, shape and color of the teliospores. 24. Their manner of germination. (See Virginia Tech. bul. 9, fig. 8, and Nebraska Rept. 22, pl. 3, fig. 5.) Make a DRAWING to show the points observed in paragraphs 17 to 24 inclusive. (See Virginia Tech. bul. 9, fig. 5-8.) There is no saprogenesis in either the primary or secondary cycles. REPORT 1. Discuss the relation of apple rust to environment. 2. Summarize the practical value of such information. BLISTER-RUST OF WHITE PINE The blister-rust of five-needled pines and its alternate phase, the felt- rust of currants and gooseberries, has recently become an important disease in eastern United States. Previous to the importation of diseased white pine nursery-stock, this disease was confined to Europe. Recently it has assumed an epiphytotic character in several localities in northeastern United States. SYMPTOMS The symptoms produced by this disease will be studied in the order of their seasonal sequence on pine, currant and gooseberry. Blister-stage on pines. In the material and illustrations referred to, NOTE :— 1. That the first evidence of the disease on the white pine is an indefinite, discolored canker-like area on the trunk or smaller branches. 2. That in some cases a slight or marked hypertrophy of the bark occurs. (See Pl. Ind. Bur. Bul. 206, fig. 3, 4 and pl. I; or Farmers’ Bul. 742, fig. 3,5 and pl. 1.) DRaw or copy. 3. That often a diseased tree may be detected by its stunted growth and bushy appearance. (See Farmers’ Bul. 742, fig. 1.) 4. That the first external evidences of the pathogene are the minute light-yellow, bladder-like swellings which exude drops of liquid. These small pustules are pycnia (spermagonia) and within them are found minute spore-like bodies called pycnospores (spermatia). These spermatia are most generally believed to be non-functioning male gametes. They do not serve in any way to propagate the fungus. Usually the pycnial stage is formed several months after infection and during the autumn just previous to the production of aecia. 5. The large hemispherical or pustular bladdery aecia pushed out from cracks in the invaded bark. DRaAw. 6. The aecia, at first yellow and enclosed by a papery peridium; later irregularly ruptured, allowing the yellow powdery contents to es- cape,—the aeciospores. The aecia are produced in early spring two or more years after infection. 7. The pock-like depressions in the bark where aecia have been borne. These characteristic markings on the cankered area constitute a reliable means of identification of diseased trees at any time of the year after the first crop of aecia has been produced. DRAW. Summer stage on currants and gooseberries. Examine the diseased ieaves of the different species of Ribes provided. OBSERVE:— 8. That in the case of certain species definite leaf-spot lesions are produced; in others the fruit-bodies of the pathogene alone constitute the first signs of the disease. DRAW. 9. The very small hemispherical pustules,—the uredinia, in groups on the under sides of the leaves. They are at first covered by the epidermis and are different in color from the remainder of the leaf, being slightly lighter green. DRAW as seen with the hand-lens. 10. That later the uredinia become more or less orange-yellow in color; the covering (composed of leaf-epidermis and peridium) is rup- tured allowing the rusty yellow contents,—the uredospores, to escape. 190 191 Felt-rust stage on currants and gooseberries. In the material of gooseberry and currant leaves provided, NOTE :— 11. The conspicuous hair-like growths,—the telia, often arising from the uredinia and more or less scattered over the entire under surface of the leaves. DRAW. In some cases the felt-rust stage accompanies the first uredina early in the summer but it is typically an autumnal stage, occurring in August and September. ETIOLOGY The blister-rust of five-needled pines is caused by the basidiomycetous rust-fungus, Cronartium ribicola Fischer von Waldheim. This name is based on the telial stage. The aecial stages of rusts, forming blister-like aecia on the bark or needles of conifers, have all been placed in the form- genus Peridermium. The blister-rust of five-needled pines 1s commonly known in its aecial stage as Peridermium strobi Klebahn. Life-history. This pathogene is a heteroecious fungus requiring two very different hosts for the development of its complete life-history. All the spore-stages produced by rusts are formed by this fungus: aecia (I) on bark of pines; uredinia (II), telia (III) and promycelia (IV) on the leaves of currants and gooseberries. The pycnia (O) are produced on the pine previous to the appearance of the aecia. Primary Cycles are initiated by the aeciospores produced in the aecia on the pine in early spring. When the peridium is ruptured, the aeciospores dust out and are blown about by the wind. Pathogenesis. The primary inoculum, aeciospores from the pine, must reach young leaves of currants and gooseberries in order to function in continuing the development of the fungus. The aeciospores cannot infect the pine. Mount some of the yellow powder from the aecia in potassium hydroxide, cover and examine with the microscope. OBSERVE :— 12. The size, shape and color of the aeciospores; thickness and markings of the spore-wall. DRAW. The aeciospores, in the presence of moisture, germinate on the under sides of gooseberry and currant leaves and the germtubes penetrate into the stomatal cavities. After the establishment of a food-relation with the host-cells surrounding the sub-stomatal cavity, a mycelium is produced which spreads in a limited area. Within about two weeks after infection the uredinia are formed. In the material studied under symptoms of this stage, NOTE :— 13. The general character of the uredinia in different stages of development. 14. The size, shape and color of the uredospores under the microscope. 15. The thickness and markings of the spore-wall. DRAW a typical uredospore showing above points. In the prepared slides showing stained sections through uredinia, NOTE :— 16. The epidermis of the leaf which was raised up and finally ruptured by the developing uredinium. 17. The peridium enclosing the contents of the uredintum. 192 18. The sporophores each bearing a single uredospore. How many nuclei in each spore? Make a DRAWING of the uredinium in section as seen under the micro- scope. The first production of uredospores furnishes inoculum for the secondary cycles, which are repeated often during the summer on currants and goose- berries. In some cases the telial stage is produced from the same mycelium which produced the first crop of uredospores, and thus the primary cycle may be carried forward to the production of sporidia from the germinating teliospores. In the prepared slides showing uredinia in section, NOTE :— 19. The stroma developed just beneath the uredinium and the radiating mycelium extending intc the host-tissue. Find a haustorium. DRAW. In prepared slides showing the telial stage, OBSERVE >-— 20. That the telial horns arise directly from the same stroma that bore the uredospores. DRAW. 21. The telial horn, composed entirely of teliospores cemented. together into a compact mass. DRAW. 22. The germination of the teliospores, forming a short germtube which is septate,—the promycelium. DRAW. 23. The sporidia produced on sterigmata from each cell of the promycelium. The sporidia, produced as the last step in the primary cycle, initiate secondary cycles on the five-needled pines. The sporidia are formed during periods of wet weather. The teliospores germinate as soon as formed, there being no rest-period required. There is no saprogenesis in the life- history of this pathogene. Secondary Cycles. There are two sorts of secondary cycles in the case of this pathogene; those initiated by sporidia on pine, and those initiated by uredospores in currant and gooseberry leaves. The repeated succession of secondary cycles, initiated by uredospores, causes the rapid spread of the fungus from the currants and gooseberries harboring the primary cycles, until by the end of summer the fungus may be disseminated over several square miles. These secondary cycles on gooseberry and currant leaves duplicate the primary cycle, in that after the uredospores are dispersed, telial horns are produced from the same stromata and upon germination of the telio- spores, promycelia bearing sporidia are formed. The sporidia of the primary and secondary cycles are the inoculum which initiate the secondary cycles on the five-needled pines. Very probably the sporidia are forcibly discharged from the sterigmata and they are blown to the pine. They are short-lived and must find suitable conditions for germination soon or they will not function. The sporidia germinate by a germtube and this penetrates uninjured pine bark initiating a new mycelium. ‘The steps in the development of the symptoms on pine have already been observed. Spermagonia may be formed in the autumn of the next year following infection. Aecia may be formed the second spring after infection or the production of the first crop of aecia may be delayed for several years. 193 From the material of affected pines, take a bit of the peridium; stain with eosin and mount in water. OBSERVE:— 24. The character of the cells of the peridium. DRAW. Study the sections through white pine twigs bearing aecia. NOTE:— 25. The position of the aecia in relation to the tissues of the twig. 26. The stroma at the base of the aecium and the radiating mycelium in the host-tissue. 27. The origin of the peridium. 28. The sporophores each bearing a chain of aeciospores. DRAW in detail an aecium with the surrounding host-tissues. REPORT 1. Illustrate graphically the steps in the primary and secondary cycles of this pathogene. 2. Illustrate graphically the nuclear phenomena exhibited during the life-history of this rust. MISTLETOE OF JUNIPERS The mistletoe of junipers is common in western and southwestern United States. A great deal of damage is annually caused by this and other mistletoe diseases of trees. SYMPTOMS In the juniper material provided, NOTE :— 1. The irregular and gnarled hypertrophies. 2. The mistletoe plants firmly rooted in the host-tissue. 3. That in many cases, the growth of the branches beyond the parasite is stopped. Make DRAWINGS showing the above symptoms. ETIOLOGY The parasite causing this disease of junipers is Phoradendron juni pert- num Englemann, one of the many species of the family Loranthaceae, a group of the flowering plants. This mistletoe has only very aborted leaves. They are mere scales closely appressed to the stem. Life-history. The inoculum in the case of the mistletoe is the small pulpy berry with its single inclosed seed. The berries are mature in Texas about December. Birds seek the berries for food and serve to a large degree as the disseminating agents. The stickiness of the pulp of — the berry causes it to adhere closely to the branch of the host. In the material provided, OBSERVE :— 4. The character of the berry, its pulpy flesh and the enclosed seed. praw. (See also bulletin mentioned below, fig. 1.) copy Pl. Ind. Bur. Bul. 166, fig. 2 and 3, showing the method of germina- tion of the mistletoe seed and the penetration of the host-tissue. The seedling establishes its root-like sinker in the conducting tissue of the host and obtains, not only water, but a certain amount of raw and modified plant-food from the host. The mature parasite blooms in December. The seeds require one year to develop and mature, so that they are ready for dissemination the next December. Pathological Histology. In the small branches of juniper cut longi- tudinally and transversely, study the roots of the mistletoe. OBSERVE :— 5. The size, shape and number of roots sent from a single plant into the host-tissue. What tissues are invaded? DRAw. In the prepared cross-sections of juniper twigs, OBSERVE :-— 6. The penetration of the host-tissues by the mistletoe root. 7. The elements present in the normal wood and bark. 8. The elements present in the root of the mistletoe. 9. The ultimate connection between the conductive elements of the host and of the parasite. Make prawincs; (a) to show diagrammatically the relation of the tissues of the host and parasite, outlining the tissues; (b) to show in detail the ultimate connection of the conductive elements. REPORT 1. Outline a practical method for the control of the mistletoes in forest areas. Explain why it should be effective. Indicate the weak points in the program. 194 OEDEMA This disease, although seldom of much importance under field condi- tions, sometimes becomes destructive in the greenhouse. It is of interest to the plant pathologist in that it is not caused by an organism, but may readily be induced by changes in temperature and humidity or by the application of dilute solutions of certain toxic substances. It affects many plants but especially tomatoes and cabbage. SYMPTOMS The cabbage leaves provided were gathered from plants in a vegetable garden. The seedlings had been grown in the greenhouse, and the plants set out in the spring. The season was cold and rainy. OBSERVE:— 1. That all the lesions are on the under side of the leaf. Is there any special reason why they should not be on the upper surface? 2. That these lesions are small raised spots, and are roughened like scab-spots on potatoes. Do they appear on the veins or on the areas between the veins? Is there any definite shape to the intumescences? Make a DRAWING of a portion of a diseased leaf. Study and sKETcH the symptoms as exhibited by potato, tomato or other plants provided. ETIOLOGY No organism is connected with this disease. It is caused by conditions which produce abnormal turgidity in the spongy parenchyma-cells of any part of the plant above the ground. It has been induced artificially by attaching the cut end of the stem to a hydrant where the water-pressure was very strong. The same result has also been accomplished by spray- ing the leaves with a dilute solution of ammoniacal copper carbonate. The larger drops always kill the tissue outright, but the smaller particles of spray cause an abnormal increase of the parenchymal cells below the epidermis. In the greenhouse, the disease results when the soil is warm, so that the roots take in a large amount of water, and the atmosphere is cold and the place poorly lighted, so that transpiration does not take place as fast as absorbtion. This causes such a pressure in the thin-walled tissues that hypertrophy and rupture result. Under direction of the instructor, the students may undertake some experiments in the greenhouse to demonstrate the causal relation of some of the factors just mentioned. Pathological Histology. Cut thin cross-sections through a lesion or use prepared slides. OBSERVE :— 3. That the lesion is made up of a number of abnormally large cells, the ends of which are entirely exposed. 4. That this exposure is due to the rupturing and the breaking- away of the epidermal cells. Are fragments of these still remaining? 5. That all the hypertrophied cells are those of the parenchyma. 6. Changes in the organs of affected cells. Make DRAWINGs to show comparatively the conditions in diseased and healthy tissues. REPORT 1. Describe in detail the procedure and results in the etiologic experiments, conducted under the instructor’s directions. 195 TERM-PAPER SUBJECTS Each term-paper exercise will consist in preparing a short paper on one of the diseases listed. The paper shall be essentially a text on the disease chosen. INFORMATION 1. The instructor will designate those subjects in the appended list from which selections for each term-paper are to be made. Any disease in the designated list may be chosen. The same subject may be chosen by more than one student, if approved by the instructor, but it is generally to the student’s advantage to have as few working on the subject as pos- sible because of the limited number of available copies of some of the articles _ to be consulted. 2. Students choosing the same subject will be expected to work independently in consulting the literature and preparing the paper. Any evidence of disregard of this expectation will rule a term-paper out of consideration. 3. If so desired, the paper may be illustrated. This is not required, but will add to its value. Illustrations may be in the form of text-figures or plates. 4. The student may write on some disease not listed herein, if permission is granted by the instructor. 5. The selection of a subject for the first term-paper will be made at the beginning of the laboratory exercise on Literature of Plant Diseases. Selection of subjects for each of the other term-papers will be made later, at a time designated by the instructor. 6. One laboratory period will be devoted to each term-paper. The work in the laboratory will consist of obtaining references and getting such information and assistance from the instructor as may be needed to make clear the method of procedure. PROCEDURE After having located and listed the references bearing on the subject chosen, as outlined in the exercise on Literature of Plant Diseases :— 7. Select three or more of the most important articles (usually the most recent). 8. Read-and abstract these carefully according to directions given in the outline on Literature of Plant Diseases, p. 13-14. 9. If specimens and materials of the disease chosen are available, they should be studied supplementary to the literature consulted. 10. Spread out the abstracts and laboratory notes and proceed to correlate and arrange the data in each, according to the following outline :— 196 197 OUTLINE FOR ARRANGING DATA IN TERM-PAPER THE BLACK ROT OF POMACEOUS FRUITS (References are to be arranged, in order of importance, thus:—) Brooks, Charles, and DeMeritt, M. Apple leaf-spot. Phyto- pant S190) pl. 17; fie. 1-6. 1912. Paddock, W. The New York apple tree canker. New York (Geneva) Agr. Exp. Sta. Bul. 163:180-206, pl. I-VI. HOSTS PLANTS AFFECTED VARIETAL SUSCEPTIBILITY OF fruit to rote! ecco: Of foliage to leaf-spot. ...................... DISEASE NAMES HISTORY AND RANGE IMPORTANCE Nature of losses. oo... MGUY TO JTUI Es © o ciecninctoc. npuTplO JOUORE. eee Reduction of yteld. Amount of losses. On the fruits {265.05 On the leaves. _..................... On thelimbs® =<... ETIOLOGY Name, history and classification of the pathogene. Pathogenicity. Life-history. 198 The Primary Cycle. 2.2555 IPANOBENESES. cccresdacenens Inoculation, “ae cee. Incubation Gse..hc ee: infections SOPTOSENCSES.S —..cskicdchinince The Secondary Cycleg..................... (If secondary cycles occur and require special considera- tion, repeat headings as for primary cycle.) ECOLOGY Pathological Histology. 0.0... Influence of climatic factors. 0.00.00... Influence of soil factors. 0....000........ CONTROL EXCLUSION Quarantine measures. 2... Elimination. 2.0.......00- Caltivation. 2.5.2.5 Rotations: asics Disinfection. 2.25.00 PROTECTION Manipulation of normal environment. 2.0. Interfering with disseminating-Agents. ecco Modifying sotl-reQcttOns., eesocssesseneene Modifying temperature-relattOns., recone Modifying motsture-relattOns. soccer Application of inhibiting substances. ................... SPRAYING. Lo eke DVS Oy eee ere Dressing and filling WOUNdS. ecsccccocseeen IMMUNIZATION Selection, 2.200... Crossing. 4.05.44 Peeding.. 3520 199 NOTES 11. The heads and subheads appearing down the middle of the page are quite definitely fixed and will be the same for any subject chosen. They should appear, properly placed, in the manuscript submitted. 12. The subheadings indicated along the left of the page will vary in character more or less, depending on the disease in hand, except in the case of those under etiology which will be uniformly the same for all diseases. 13. Additional subheads of the type at the left of the page may be inserted where the nature of the data requires it. 14. Omission of heads and subheads is to be made when there are no data to record thereunder. 15. References in the body of the text should be inserted at the end of the sentence. Where one of the references in the list at the beginning of the paper is to be referred to, enclose in parenthesis the author’s name, date of publication, colon and page, thus:—(Jones, 1914:27). The author’s name may be omitted when it is clear, from the context, to which article reference is made. When an article not listed in the references given at the beginning of the paper, is to be cited, the parenthetical insertion must include the author’s name, name of publication (abbreviated), volume or its equivalent, colon, and pages on which the data are to be found, thus:—(Duggar, Fungous Dis. p. 237. 1909) or (Peck, Journ. Myc. 7:10-14). 16. Confine the discussion to the disease on the host or hosts specified and to closely related hosts. 17. The reference-sheets, including the abstracts, must be handed in with the term paper. LIST OF SUBJECTS FIELD CROPS 1. Alfalfa root-gall caused by Urophlyctis alfalfae Magnus. 2. European root-rot of alfalfa caused by Rhizoctonia Crocorum Fries. 3. Alfalfa stem-blight caused by Bacterium Medicaginis (Sackett) E. F. Smith. 4. Smuts of barley caused by Ustilago Hordet (Persoon) Kellerman and Swingle, and Ustilago nuda (Jensen) Kellerman and Swingle. 5. Clover anthracnose caused by Colletotrichum Trifolit Bain (=C. caulivorum Kirchner). 6. Clover rusts caused by Uromyces Trifolit (Hedwig) Léviellé on white clover, and Uromyces fallens (Desmazieres) Kern on red clover. 7. Stem-rot of clover caused by Sclerotinia Trifoliorum Eriksson. 8. Ear-rot of corn caused by Diplodia Zeae (Schweinitz) Léviellé. 9. Cotton anthracnose caused by Glomerella Gossypii (Southworth) Edgerton (=Colletotrichum Gossypti Southworth). to. Root-rot of cotton and alfalfa caused by Ozontum omnivorum Shear. . 11. Helminthosporium diseases of cereals caused by Helminthosporium gramineum (Rabenhorst) Eriksson, H. teres Saccardo, H. sativum Pammel King and Bakke and H. turcinum Passerini. 200 12. Downy mildew of grasses caused by Sclerospora graminicola (Sac- cardo) Schroeter. 13. Hop mildew caused by Sphaerotheca Humuli (Fries) Burrill. 14. Crown-rust of oats caused by Puccinia Lolit Nielson (=Puccinia coronata Corda.) 15. Early blight of potatoes caused by Alterania Solani (Ellis and Martin) Jones and Grout (=Macrosporium Solani Ellis and Martin). 16. Leaf-roll and curly-dwarf of potatoes, cause unknown. 17. Black leg of potatoes caused by Bacillus phytophthorus Appel (= Bacillus Solanisaprus Harrison, = Bacillus atrosepticus van Hall, = Bacil- lus melanogenes Pethybridge and Murphy). 18. Potato scab caused by Actinomyces chromogenus Gasperini (= Sirep- tothrix scabies (Thaxter) Cunningham, =Oospora scabies Thaxter). tg. Black wart of potatoes caused by Chrysophlyctis endobiotica Schilbersky. 20. Brown rot or wilt of Solanaceae (potatoes, tomatoes and tobacco) caused by Bacterium Solanacearum E. F. Smith (=Bacillus Solana- cearum E. F. Smith, = Bacillus Nicotianae Ueda). 21. Rice blight or blast caused by Piricularia grisea (Cooke) Saccardo. 22. Rice smut caused by Tilletia horrida Takahashi. 23. Cobb’s sugar-cane disease caused by Bacterium vascularum (Cobb) G. Smith. 24. Root disease of sugar-cane caused by Marasmius plicatus Wakker. 2s. Smuts of sorghum caused by Sphacelotheca Sorght (Link) Clinton, Ustilago cruenta Kithn and Sphacelotheca Reiliana (Kithn) Clinton. 26. Timothy smut caused by Ustilago striaeformis (West.) Niessel. 27. Timothy rust caused by Puccinia Phlei-pratensis Eriksson and Henning. 28. Root-rot of tobacco caused by Thielavia basicola (Berkley and Broome) Zopf. 29. Wheat scab caused by Fusarium cumorum (W. G. Smith) Saccardo. 30. Flag-smut of wheat caused by Urocystis Tritict Kornicke and the stem-smut of rye caused by Urocystis occulata (Wallroth) Rabenhorst. 31. Take-all of wheat caused by Ophiobolus graminis Saccardo or Ophiobolus herpotrichus (Fries) Saccardo. 32. The role of insects in the dissemination of pathogenic fungi. FRUIT CROPS 33. Fruit-spot of apple caused by Phoma Pomi Brooks (=Cylindro- sporium pomt Brooks). 34. European apple tree canker caused by Nectria galligena Bresadola. 35. Blister-canker of apple caused by Nummularia discreta (Schweinitz) Tulasne. 36. Northwestern anthracnose of apple caused by Neofabrea malicorticts (Cordley) Jackson (=Gloeosporium malicorticis Cordley). :37. Apple rots caused by the following ascomycetous pathogenes; Alternaria sp., Cephalothecium roseum Corda., Volutella fructi Stevens and Hall, Endomyces Mali Lewis, Sclerotinia cinera (Bonorden) Schroeter. 38. Water-core of apple, cause not definitely known. 39. Crown-gall of apple and other fruit-trees caused by Bacterrum tumefaciens E. F. Smith and Townsend. 201 4o. Gummosiscaused by Bacterium Cerasus (Griffin) (= Bacillus spongio- sus Aderhold and Ruhland). 41. Leaf-blight (shot-hole or yellow-leaf) of cherries caused by Coc- comyces hiemalis Higgins (=in part, Cylindrosporium Padi Karsten). 42. Powdery mildew of cherry caused by Podosphaera Oxyacanthae (Fries) de Bary. 43. Citrus canker caused by Bactertum Cuitri (Hasse) E. F. Smith (=Psendomonas Citri Hasse). 44. Sooty mold of citrus caused by Meliola Penzigt Saccardo (=M. Cammeliae (Cattaneo) Saccardo). 45. Citrus scab caused by Cladosporium Citri Massee. 46. Wither-tip of citrus caused by Glomerella cingulata (Stoneman) Spaulding and von Schrenk (=Colletotrichum gloeosporoides Penzig). 47. Blue mold or rot of citrus caused by Penicillium digitatum (Fries) Saccardo, P. Italicum Wehmer and P. expansum Link. 48. Brown rot and canker or gummosis of citrus caused by Pythiacystis Citrophthora E. H. Smith and R. E. Smith. 49. Pod-rot and canker of cocoa caused by Phytophthora Fabert Mau- blanc. 50. Leaf-spots of coffee caused by Pelliculiaria Koleroga Cooke, Stil- bella flavida (Cooke) Kohl. and other fungi. 51. An anthracnose of currants caused by Pseudopeziza Ribis (Libert) Klebahn (=Gloeosporium Ribis (Libert) Montagne and Desmazieres. 52. The European currant rust caused by Cronartium Ribicola Fischer von Waldheim. 53. Powdery mildew of gooseberries and currants caused by Sphaero- theca Mors-uvae (Schweinitz) Berkley and Curtis. 54. Silver-leaf of fruit-trees caused by Stereum purpureum Fries. 55. Root-rot of fruit trees caused by Armillaria mellea (Fries) Quélet and Clitocybe parasitica Wilcox. 56. Injury to fruit-trees caused by frost. 57. Grape anthracnose caused by Gloeosporium ampelophagum (Pas- serini) Saccardo (=Sphaceloma ampelinum de Bary). 58. Dead arm or necrosis and ripe rot of grapes caused by Cryptosporella Viticola (Reddick) Shear (=Fusicoccum Viticolum Reddick). 59. Powdery mildew of grapes caused by Uncinula necator (Schweinitz) Burrill. 60. Olive knot caused by Bacterium Savastanot E. F. Smith (= Bacrllus olea-tuberculosis Savastano). 61. Black spot or bacterial shot-hole of peaches and plums caused by Bacterium Pruni E. F. Smith. 62. California peach blight caused by Coryneum Beijrinckit Oudemans. 63. Leaf-blight (shot-hole, yellow-leaf) of plums caused by Coccomyces Prunophorae Higgins (=in part, Cylindrosporium Padi Karsten). 64. Die-back and canker of peaches and plums caused by Valsa leucos- toma Fries. 65. Peach scab caused by Cladosporium carpophilum Thimen. 66. Plum pocket caused by Exoascus Pruni Fuckel. 67. Powdery mildew of the peach caused by Sphaerotheca pannosa (Fries) Léviellé. 68. Rust of stone-fruits caused by Puccinia Prunt-spinosae Persoon. 69. Peach yellows, cause unknown. 202 70. Little peach, cause unknown. 71. Leaf-spot of pear caused by Mycosphaerella sentina (Fries) Schroeter (=Septoria Pyricola Desmazieres). 72. Pear scab caused by Venturia Pyrina Aderhold. 73. Rust of the pear caused by Gymnosporangium globosum Farlow. 74. Leaf-blight and fruit-spot of quince and pear caused by Fabrea maculata (Léveillé) Atkinson (=Entomosporium maculatum Léveillé). 75. Rust of quince caused by Gymnosporangium clavipes Cooke and. Peck. 80. Anthracnose of raspberries and blackberries caused by Gloesoporium. venetum Spegazzini. 81. Orange-rust of raspberries and blackberries caused by Gymnoconia interstitialis (Schlectendall) Lagerheim (=Caeoma nitens (Schweinitz) Burrill). 82. Cane-blight of raspberries caused by Leptosphaeria Contothyrium (Fuckel) Saccardo. 83. Double blossom of dewberry caused by Fusarium Rubt Winter. 84. Powdery mildew of strawberries caused by Sphaerotheca Humult (Fries) Burrill. GARDEN CROPS . Bean blight caused by Bactertum Phaseolt E. F. Smith. a Downy mildew of lima-beans caused by Phytophthora Phaseoli Thaxter. 87. Bean rust caused by Uromyces appendiculatus (Persoon) Léviellé. 88. Beet rust caused by Uromyces Betae (Persoon) Tulasne. 89. Heart-rot and leaf-spot of beets caused by Phoma Betae Frank. go. Black leg and yellows or wilt of cabbage caused respectively by Phoma oleracea Saccardo and Fusarium conglutinans Wallenweber. gt. The white rust of crucifers caused by Albugo candida Kuntze (=Cystopus candidus Léviellé). 92. Early blight of celery caused by Cercospora Api Fries. 93. Leaf-spot and stem-rot of clematis caused by Ascochyta Clematidina Thumen. 94. Sweet corn wilt or Stewart’s sweet corn disease caused by Bacterium Stewartit E. F. Smith. 95. Scab of cucumbers caused by Cladosporium cucumerinum Ellis and Arthur. 96. Wilt of cucurbits caused by Bacillus trachtephilus E. F. Smith. 97. Angular leaf-spot of cucumbers caused by Bacterium lachrymans E. F. Smith and Bryan. 98. Powdery mildew of curcurbits caused by Erystphe cichoracearum Fries. 99. Downy mildew of ginseng caused by Phytophthora cactorum (Cohn and Lebert) Schroeter. too. Alternaria blight of ginseng caused by Alternaria Panax Whetzel. to1. Yellow disease of hyacinth caused by Bacterium hyacintht (Wak- ker) E. F. Smith. to2. Lilac blight caused by Phytophthora Syringae Klebahn. 103. Blight of peas caused by Mycosphaerella pinodes (Berk. and Blox.) Stone (=Ascochyta pisi Libert) 104. Root-rot of peas, beans, tobacco and ginseng caused by Thielavia basicola (Berkley and Broome) Zopf. 208 ros. Dry-rot of sweet potatoes caused by Diaporthe Batatis Harter and Field (=Phoma Batatae Ellis and Halsted). 106. Soft rot of sweet potatoes and leek of Irish potatoes caused by Rhizopus nigricans Ehrenberg. 107. Stem-rot of sweet. potatoes caused by Fusarium Batatatis Wollen- weber or F. hyperoxysporium Wollenweber. 108. Scurf of sweet potatoes caused by Montlochaetes infuscans Halsted. tog. Fruit-rot of tomato caused by Phoma destructiva Plowright. t10. End-rot of tomatoes; cause variously assigned. r11. Leaf-spot or blight of tomatoes caused by Septoria Lycopersict Spegazzini. 112. Leaf-mold of tomatoes caused by Cladosporium fuluum Cooke. FOREST TREES 113. Twig-blight of conifers caused by Pestalozzia funerea Desmazieres. 114. Twig-bligh of conifers caused by Herpotrichia nigra Hartig. (=Neopeckia Coultert (Peck) Saccardo). r1s. Walnut blight caused by Bacterium Juglandis (Pierce) E. F. Smith. 116. Fir blight caused by Botrytis Douglas Tubeuf. 117. Leaf-blight of fir and spruce caused by Trichosphaeria parasitica Hartig (=Acanthostigma parasitica (Hartig) Saccardo). 118. Tar-spot of maple leaves caused by Rhytisma acerinum Fries and R. punctatum Fries. 119. Twig-blight of pine caused by Cenangium Abtetis Rehm. 120. Leaf-spots of walnut and poplar caused respectively by Gnomonia leptostyla (Fries) Cesati and de Notaris (=Marssonia Juglandis (Lebert) Saccardo) and Trochilia Populorum Desmazieres. 121. Powdery mildew of chestnut caused by Phyllactinia Corylea Karsten. 122. Powdery mildew of oaks in Europe caused by Muzcrosphaera Alni (Fries) var. Quercina Neger. 123. Canker of maple and other trees caused by Nectria cinnabarina Fries (= Tubercularia vulgaris Fries). 124. Canker of spruce caused by Nectria cucurbitula Fries. 125. Canker of spruce and fir caused by Pestalozzia Hartigi: Tubeuf. 126. Root-rot of conifers caused by Rhizina undulata Fries (= Rhizina inflata Quélet). 127. Root-rots of trees caused by Rosellinia sps. 5 128. Root-rot of forest-trees caused by Armillaria mellea (Fries) uélet. 129. Red-rot of conifers caused by Fomes Pinicola (Fries) Cooke. 130. Decay of oak, beach and other trees caused by Bulgaria poly- morpha Wettstein (=B. inquinans Fries). 131. Heart-rot of forest-trees caused by Polyporus sulphureus Fries. 132. Heart- and sap-rot of trees caused by Polystictus versicolor Fries. 133. Compare and contrast symptoms produced by Polystictus versi- color Fries, Polystictus pergamenus Fries, Merulius lacrymans Fries and Fomes Pinicola (Fries) Cooke. 134. Compare and contrast symptoms produced by Polyporus squamo- sus Fries, Polyporus sulphureus Fries, Polyporus Betulinus Fries, Hydnum septentrionale Fries. 204 135. Compare and contrast symptoms produced by Trametes Pini Fries, Lenzites sepiaria Fries, Polyporus subacidus Peck, Polyporus carneus Fries and Polyporus rimosus Berkley. 136. Compare and contrast symptoms produced by Armillaria mellea (Fries) Quélet, Fomes annosus (Fries) Cooke, Polyporus Schweinitztt Fries and Thelephora galactina Fries. 137. Compare and contrast symptoms produced by Fomes tgnarius (Fries) Gillet, Fomes appalanatus Wallroth, Fomes Fraxanophilus (Peck) Saccardo Fomes fomentarius (Fries) Gillet. 138. Host-index of wood-rotting fungi arranged under the names of the fungi. 139. Host-index of wood-rotting fungi arranged under the names of the hosts. 140. Leaf-burn of trees. 141. Smoke and gas injury to trees. 142. Winter injury to trees. 143. Mycorrhiza of tree-roots. GLOSSARY* Agent of inoculation.—The thing which acts as the carrier in the transfer of the inoculum from its source to the infection-court, as for example :— wind, insects or running water. Control.—The prevention of losses from a disease. Every control measure is based on one of four fundamental principles; exclusion, eradication, protection or immunization. Dissemination.—The act or manner of scattering or spreading the inocu- lum of the pathogene within an immediate and more or less limited area about the source of inoculum. Distribution.—(a) The act of transporting and establishing a pathogene beyond barriers in other regions. (b) The geographical occurrence of the disease; synonymous with range. Ecology.—That phase in the study or discussion of a disease which deals with the relation of environmental factors to its occurrence, severity and character. The ecologic factors are chiefly, climatic, soil and cultural. They influence the disease indirectly through their in- fluence on the pathogene or the host or on both. Enphytotic.—The opposite of epiphytotic. An enphytotic disease is one regularly occurring in a locality or region and not liable to marked variations in destructiveness. Epiphytotic.—The sudden and destructive appearance of a plant disease in a locality or region. An epiphytotic disease is one the past history of which shows it to have a tendency to appear suddenly and destruc- tively, usually over large areas at rather long intervals. The term is analogous in meaning to epidemic but not synonymous with it. Eradication.—The principle of controlling a plant disease by removing or destroying the pathogene already established within a given area or region. Disinfection, seed-selection, crop-rotation and the like are eradicatory measures. : Etiology.—That phase in the study or discussion of a disease, which deals with the chief causal factor, the pathogene, its nature, character and relations with the host. Exclusion.—The principle of controlling a disease in plants by excluding the pathogene from a given area or region. Inspection and quaran- tine are the exclusionary measures usually employed. History of a disease.—The logically arranged historical facts, relating to the disease itself, as distinguished from those relating more es- pecially to the pathogene. Host.—The plant affected with, or subject to a given disease. Hyperplasia.—That type of pathological condition expressed by abnormal increase in the number of cells, that is, excessive cell-division. Hypertrophy.—That type of pathological condition expressed by abnormal increase in size of cells (dimensions or volume). The term is also commonly used in a less restricted sense to designate swellings or overgrowths of various kinds, due either to abnormal increase in the size of the cells or abnormal cell-division or both. (See p. 8.) *The definitions apply to the respective terms only as these terms are used in a phytopathological sense, and particularly as used in these outlines. The definitions do not always agree with those to be found in dictionaries, nor always with the variety of senses in which the terms are used even in phytopathological literature. 205 206 Hypoplasia.—That type of pathological condition expressed by the failure of plant-cells or organs to complete, in one or more respects, their — normal development, that is, arrested development. Dwarfing, failure of chlorophyl-development and the like, are examples. Hypoplastic diseases.—See p. 8. Immunization.—The principle of preventing losses from a plant disease by the development of resistant or immune strains of the crop. This may be accomplished by selection and propagation of naturally resistant or immune individuals, by segregation and propagation of resistant or immune individuals obtained by crossing immune and susceptible forms or, artificially by feeding or injecting into susceptible hosts, substances which will make them resistant or immune. ‘The last has, as yet, little or no practical value. Incubation.—The activities and developments of the pathogene from the moment of its arrival in the infection-court until it has established a pathologic relation with the host. Incubation period.—The period beginning with the arrival of the inoculum in the infection-court and ending with the first evidence of disease. Infect.—To initiate or produce disease. Infection.—The act of producing or initiating a diseased condition in the tissues of the host. Infection is progressive, developing cell by cell and continues as long as the host continues to react to the stimulus of the pathogene. Infection-court.—The place on or in the host where the incubation- activities of the pathogene take place; the immediate neighborhood of a possible point of infection. Infection period.—Commonly used to designate the period during which conditions (of host, pathogene, and environment) are especially favorable to inoculation, incubation, and initial infection, or to incuba- tion and initial infection only. Inoculate.—To transfer the inoculum from its source to the infection- court. Inoculation.—The act of inoculating. It includes all the phenomena in- volved in the transfer of the inoculum from its source to the infection- court. Inoculum.—That structure of the pathogene which may be transferred from its source to the infection-court. It usually consists of spores, seeds, eggs, thalli (of bacteria), or even mycelial fragments or pieces of stems (Cuscuta). Lesion.—A definite region in a plant or in one of its organs, characterized by a pathologic change in structure. Life-cycle.—The succession of phenomena exhibited during a period of continuous growth and development of the pathogene (in a fungus, from spore-germination to the normal death of the mycelium thus initiated). Most pathogenes exhibit in their life-cycles two rather distinct phases, pathogenesis and saprogenesis. Life-history.—The complete succession of phenomena characterizing a pathogene throughout the various cycles of its existence. Metaplasia.—That type of pathological condition expressed by the overgrowth in cells, other than increase in size (hypertrophy) or numbers (hyperplasia). Abnormal starch accumulation, abnormal development of chlorophyl, unusual thickening of cell-walls and abnormal nuclear division or growth are evidences of metaplasia. 207 Sometimes used in a less restricted sense to include all types of over- growth. Metaplastic diseases.—See p. 8. Necrosis.—That type of pathological condition expressed by the rapid destruction of cell-structures and a consequent prompt death of the protoplasts; rots, blights and cankers are examples. Necrotic diseases.—See p. 7. Pathogene.—Any factor capable of initiating disease (usually a living organism). Pathogenesis.—That portion or phase of a life-cycle during which the pathogene becomes and continues directly associated with the living host. Pathogenesis includes inoculation, incubation and infection. Pathogenicity.—The ability of an organism to produce disease. Pathogenicity studies.—Experimental studies demonstrating the patho- genicity of a given organism. Pathological anatomy.—That phase of phytopathology which deals with pathologic changes in form, appearance, arrangement and relation of tissues in plant-organs (gross internal symptoms). Pathological histology.—That phase of phytopathology which deals with pathologic changes in the individual cells of plant-tissues. Pathological morphology.—That phase of phytopathology which deals with pathologic changes in form, size, color and the like, of plants or plant-organs (gross or external symptoms). Primary cycle.—A life-cycle initiated by a primary infection. Primary infections.—Those infections first initiated by the pathogene after a period of rest or relative inactivity. In temperate regions, pathogenes usually initiate their primary infections in spring or early summer. Protection.—The principle of controlling a plant disease by placing some protective barrier between the host and the generally-present patho- gene. Spraying, dusting and coating with substances inimical to the inoculum of the pathogene but harmless to the host are the usual protective measures employed. Range.—The geographical regions, areas or countries in which the disease is known to occur. Saprogenesis.—That phase of a life-cycle during which the pathogene is not in direct association with the living host. Saprogenesis in- cludes the saprophytic activities and dormant period of the patho- gene. Some pathogenes exhibit no true saprophytic activities during saprogenesis; some exhibit no saprogenesis, being continu- ously associated with the living host. Secondary-cycle.—A life-cycle initiated by a secondary infection. Secondary infections.—Those initiated by inoculum from the primary or other secondary infections without an interposed resting or dormant period. Symptoms.—Those pathologic changes by which a diseased plant is distinguished from a healthy one. For names and definitions of different kinds of symptoms, see pages 7-8. Signs.—Incidental or experimental evidences of disease as distinguished from pathological evidences. For names and definitions of some of the more usual signs of disease in plants, see pages 8~9. Source of inoculum.—The place or object on or in which the inoculum is produced. LIBRA tut 14199