346 DISEASES OF CROP-PLANTS 



and drooping of the leaves, beginning with reddish discoloration 

 and resulting in withering from the tips, loss of colour, and eventu- 

 ally the complete drying-up of the plant, frequently when the 

 fruits are partly grown. 



Examination of the plants in various stages of failure showed 

 quite clearly that it was a question of root decay. The worst 

 affected plants had hardly any functioning roots, the least affected 

 were fairly well provided, and the intermediate forms showed 

 corresponding gradation. In all the specimens the actual 

 tissues of the stems, apart from the discoloured root traces, were 

 quite sound, thus differentiating this disease from stem base-rot 

 due to Thielaviopsis. 



Associated Fungi. 



In the affection as met with by the writer and as described 

 by previous investigators in the West Indies fungus hyphae 

 have been found in the roots and root-hairs from an early stage 

 of failure. Their presence is referred to by most writers on the 

 subject but in itself is not of much value as evidence of their 

 pathogenic nature, especially as no particular fungus has been 

 found to be well-marked and constant, Fusarium and other 

 soil-inhabiting tj^pes are met with, but in no case has a necessary 

 connection with the disease been demonstrated. On several 

 occasions the mycelium and fructifications of Marasmius Sacchari 

 have been associated with diseased plants in the West Indies, 

 but this is not by any means general. 



C. W, Carpenter has demonstrated very recently that wilt 

 in the Hawaiian Islands is due to destruction of the finer roots by 

 a fungus which he considers to be identical with Pythium butleri 

 Subram. the cause of root rots of tobacco and ginger and foot-rot 

 of Carica papaya in India, 



Control. 



Until the particular types of affection included under the name 

 of root disease have been investigated and defined there is not 

 much that can usefully be said on the subject of control. 



So far as the disease is primarily due to some unfavourable 

 condition or conditions of growth, including physically unsuitable, 

 poorly prepared, insufficiently drained and cultivated soil (all 

 leading to a restriction of aeration), poverty of soil, lack of water, 

 and poorly prepared planting material, the means to be taken are 

 obvious. There can be no doubt that much of the trouble 

 experienced has originated in this way 



The appearance of communication from plant to plant and 

 the way in which the trouble slowly extends over the beds, as 

 described above, afford fairly convincing evidence that para- 

 sitism is an important factor in at least one form of the disease. 

 Its existence in an affection of this nature introduces the usual 



