DISEASES OF PINES. 57 



or because the weather is so hot and dry that there is not enough 

 water in the immediate environment at all. 



Different as are the above causes of premature leaf-casting, there 

 are still others, of which the following is the most prevalent and 

 difficult to deal with. The leaves turn yellowish, with brown and 

 purplish spots and patches on them, and fall in showers as before ; 

 but this time the disease is found to be epidemic in character. 

 Towards the end of the summer numerous tiny black spots may be 

 observed on the dying and dead leaves, and these are the spermo- 

 gonia of a definite fungus (Hysterimn Pinastri, one of the Phacidiaccce 

 of the Discomycetes). In wet seasons, or if the leaves be kept moist 

 through the winter, the higher fructifications and asci may be obtained. 

 Researches have shown that Goppert* was quite right, so long ago 

 as 1852, in attributing this epidemic to the ravages of the mycelium 

 of the above fungus ; the hypha: invade the leaf tissues during wet 

 seasons, kill the cells, and so bring about the browning of the 

 " needles." When large quantities of needles have been thus ruined, 

 they suddenly fall in the showers which bring dismay to the forester 

 and horticulturist, and give the name " shedding " (Scliutte of the 

 German foresters) to the disease. 



These are not the only causes of premature leaf-casting in Conifers, 

 but they are good examples of the commonest types, and I have 

 brought them forward here to show you how very easy it is for 

 anyone unacquainted with the facts to draw erroneous conclusions as 

 to the causes of the phenomena; and it must be remembered that 

 wrong conclusions i.e., wrong diagnoses lead to improper treatment 

 in plant-diseases, as they do in human diseases. The diseases of 

 Conifers are, in fact, like the diseases of other living beings, cases 

 of disturbances in the struggle for existence going on among the 

 structural elements of the tissues, etc. The discussion is here confined 

 to only two categories of these diseases those due to fungi and those 

 due to disturbing action of the inorganic environment ;j- the simplest 

 plan will be to take some of the groups of Conifer* seriatim, and 

 touch briefly on their prominent maladies. 



I. The Pines. Owing to their very resinous nature, the Pines generally 

 are not so apt to suffer from injuries which result from the exposure of 

 open wounds as are many other trees, and it is astonishing how much 

 knocking about the hardy species will endure ; breakages from wind, heavy 

 snow, the cutting and biting of man and other animals, and so forth, 

 are readily healed* over by occlusion in the case of most of the species. 



A very common cause of disease and death in Pines is the breaking of the 

 ascending water-current from various actions of an unsuitable environment. 



* " Verhandlungen des schlesischen Forstvereins," 1852, p. 67. 



t Those diseases which are due to the injurious action of animals, especially insects, being 

 treated of separately. 



