90 DISEASES OF TROPICAL PLANTS CH . 



spores are borne in the brown mass in the centre. The 

 leaf gradually dries up. Other similar leaf-spots of less 

 importance are the eye-spot (C. sacchari, Br. de H.) 

 of Hawaii and Java; the red spot (C. vaginae, Kr.) of 

 Java, India, and West Indies ; the black spot (C. 

 acerosum, D. and H.) of Java, and (C. kopkei, Kr.) of 

 Java, and the yellow leaf-spot (Pestalozziafuscescens, 

 Sor. , var. sacchari, Wakker) of Java. 



Wither Tip. This is a leaf disease which has been 

 reported from Hawaii by Cobb. It is not very serious 

 and appears only at intervals. It is most abundant on 

 the blades, causing them to die from the tip backwards. 

 The blades lose their colour on the tips and in streaks 

 which vary from ^ inch to nearly half the width of the 

 leaf. Finally the entire leaf is dead with the exception 

 of the midrib. One of the most characteristic features 

 of the disease is the abrupt contrast between the dead 

 and living part of the leaf. The disease is apparently 

 due to an undetermined fungus. 



The term root disease is somewhat general, since it 

 no doubt includes root diseases which have many 

 different causes. Some of the most important of these 

 diseases have been very ably discussed by Prof. N. A. 

 Cobb, 1 from whose work much of the information here 

 given has been drawn. They are the most destructive 

 of the known diseases of the cane, partly because they 

 are more or less obscure for a considerable period, and 

 partly .because their location makes it especially difficult 

 to apply any satisfactory remedy economically. 



Ithyphallus (Fig. 41) is a fungus which is said to be 

 the cause of one of the most important root diseases 

 known, although it is not so widespread as some others. 

 The injury to the root system is not so apparent to the 

 observer, unless it is studied with the aid of the micro- 

 scope. However, as the new shoots come through the 

 ground they are found to be covered with masses of 

 the white mycelium of the fungus. If this mycelium is 



1 "Fungus Maladies of the Sugar-cane," Bui. 5, Experiment Station of the 

 Hawaiian Sugar Planters' Association. Div. of Plant Pathology and Physiology. 



