Plant Sanitation. 



20 



[Jan. 1908. 



they are infested with the mycelium of a fungus, for when the leaves become dry 

 and hang down the fructifications push through the epidermis and form pustules of 

 varying size and shape. Eventually, when the vitality of the tree has been reduced, 

 the terminal bud as already noticed becomes infested with a ' rot ' svhich causes the 

 whole cabbage to fall over, resulting in the death of the tree. 



Specimens of leaves, roots, stems, petioles, &c, were taken from a con- 

 siderable number of diseased trees for examination and for cultural and infection 

 experiments. Although it has been impossible to establish with certainty the 

 whole of the life history of the fungus in the short time that has been given to the 

 study of this disease, yet some interesting points have been established. 



Microscopic examination of diseased roots was made in longitudinal and 

 transverse sections. At once it was noticed that the cortex of the roots was 

 abnormal. 



In a diseased root, the walls of the cortex cells appear to be shrunken and 

 the cells are turgid no longer. Between the walls of consecutive cells can be seen 

 large dark-coloured septate threads of a fungus mycelium, while many of the cells 

 themselves have become invaded by the same. When a cortex cell is threatened by 

 the approach of a fungal thread, its cell contents appear to be altered, for large 

 yellowish globules make their appearance. Whether these have been produced by 

 the cell itself as a means of protection against the fungus, or whether they are the 

 result of decomposition could not be determined, but after the mycelium has gained 

 an entrance into the cell, these globules as well as all the other cell contents are 

 destroyed and absorbed. 



The mycelium of the fungus spreads from one cell to another by piercing 

 through the cell walls, and soon obtains an entrance into the thin-walled cells of the 

 central cylinder and eventually into the vessels themselves. 



The red discolouration of the stem was carefully examined microscopically, but 

 except in the case of trees that were very badly diseased, few mycelial threads could 

 be detected. These in the advanced cases were similar to those noted in the roots, 

 but I am of opinion that the red discolouration is primarily due to the disorganiza- 

 tion of normal changes in the stem through the stoppage of supplies from the roots, 

 rather than to any effect of the small amount of fungal mycelium found in diseased 

 stems. 



Petioles.— It was observed that almost without exception, the petioles of 

 the leaves of badly diseased trees showed a large number of minute ruptures of the 

 epidermis, after they had died and had fallen to the ground. The petioles in varying 

 stages of disease were therefore submitted to a careful microscopic examination, and 

 it was observed that a mycelium of a fungus was found in all diseased petioles. 



The point of the first attack could not be determined, but it would appear 

 that the petiole, just where it expands to ensheath the stem of the tree, is the part 

 where the effect of the fungus is first noticed. The whole petiole gradually assumes 

 a blackish colour, the leaflets become brown, and eventual^ on the dead petioles 

 minute ruptures take place in the epidermis of the petiole just where it begins to 

 expand before joining the stem. These give off a black powdery dust, which 

 consists of spores of two kinds— one, single-celled and colourless, and the other two- 

 celled and brown. 



The two-celled spores suggested that the fungus belonged to the genus 

 Botryodiplodia, and therefore specimens were forwarded to Dr. N Patouillard, who 

 has recently described several new specimens of fungi on coconuts from French 

 Polynesia for identification and he reports as follows :— 



"I have examined the specimens of parasitic fungi on petioles of coconut. 



