DIFFICULTIES IN THE OUTSET. WHAT CONSTITUTES DISEASED ACTION. NO ANALOGY TO ANIMAL SICKNESSES. CONGENITAL DEFECTS. DEBILITY. DEFICIENT STRENGTH OF FIBRES. DEFECTIVE FOLIAGE. IMPERFECT AND REDUNDANT BLOSSOMS. THE CIVILIZED AND CULTIVATED PLANT MAY BE ABNORMAL ALTOGETHER. UNSATISFACTORY ACCOUNTS OF DISEASES IN PLANTS. LANKESTER'S CLASSIFICATION CONSIDERED. EFFECTS OF THE EXCESS OR PAUCITY OF MOISTURE, HEAT, AND LIGHT. MODE OF ACTION OF FROST. INJURY RATHER REFERRIBLE TO THE CONDITION OF THE CIRCULATION THAN TO THE DEGREE OF COLD IN MANY HARDY PLANTS. INFLUENCE OF THE SOIL. LIGHT THE GREAT STIMULUS, ITS WITHDRAWAL SUSPENDS HEALTHY ACTION. ITS SUDDEN RESTORATION CAUSES DEATH BY SUN SCALD. INJURY BY SUNSHINE IN WINTER. POISONOUS GASES. MIASMATA. POISONS IN THE SOIL. PARASITIC PLANTS, EPIPHITES, FUNGI, PEAR BLIGHT. VARIOUS THEORIES. WHAT WE KNOW, AND WHAT WE DON'T KNOW. TREATMENT. ROOT PRUNING SUGGESTED. SATISFACTORY RESULTS. MILDEW BLIGHT IN PEACH AND APPLE. TWIG BLIGHT IN APPLE AND QUINCE. THE APPLE BLIGHT. BITTER ROT. CRACKED FRUIT. SCAB. MILDEWS. KIRTLAND'S VIEWS AND SUGGESTED REMEDY. WOUNDS AND INSECTS. NEEDING THE AID OF SURGERY RATHER THAN MEDICINE. DESTRUCTION OF FOLIAGE BY INSECTS IMPAIRS THE HEALTHY CONDITION OF THE PLANT. RESUME. SELECT HEALTHY TREES OF HEALTHY VARIETIES. EMPIRICAL CHARACTER OF TREATMENT USUALLY RECOMMENDED FOR DISEASED TREES. THE BLACK KNOT. THE ROT AND MILDEW OF THE GRAPE.