874 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



No. 55, February, 1904 ; 8 plates). — This bulletin deals with a Potato 

 disease common over a considerable portion of the United States, and 

 also known in Europe. It is variously known as bundle blackening, stem 

 rot, dry end rot, and dry rot. Bundle blackening and dry end rot, of the 

 tuber, are two stages of the same disease. This begins in the field in the 

 underground stems and roots. A fungus is always present in the 

 darkened vascular bundles of the tubers, which has been shown to be a 

 Fusarium. 



The above-ground symptoms are slow change of colour, dwarfing, 

 more or less rolling or curling of the leaves, and finally a wilt of the 

 foliage and the falling down of the stems. The first symptoms in the 

 tuber are nearly always at the stem end, in the form of browned or 

 blackened vascular bundles. During this stage the tubers are sound ex- 

 ternally. The dark stain may extend to the eye end of the tuber, the 

 parenchyma remaining sound, or becoming yellowish, or finally shrivelled 

 and greyish-brown, or else breaking down with mixed infections, including 

 bacterial rot. 



The fungus grows readily in a great variety of culture media. It varies 

 considerably in form, colour, and sporification according to the environ- 

 ment. Under varying conditions various colours were obtained — purple, 

 violet, lilac, pink, rose, yellow, cream, salmon, cinnamon, grey, and green. 

 Macroconidia were more abundant in some media than in others, and in 

 certain media only were chlamydospores produced. 



The fungus attacks the plant from the soil, and winters over in the 

 earth. In land frequently planted with Potatos it can probably main- 

 tain itself indefinitely. A copious use of fertilisers did not enable the 

 plants to overcome the disease. 



The disease continues in stored Potatos, and if they are kept in warm 

 rooms the loss during the winter is likely to be large. Those stored in a 

 cool place keep much better. Diseased tubers should therefore be stored 

 in cool, dry rooms, and used early in the season. 



Infected lands should be planted with other crops for a series of years, 

 but excluding Tomatos, Egg plants, and similar plants. Care should be 

 taken not to infect healthy land by planting diseased tubers. Diseased 

 tubers should not be thrown on the manure heap. 



The following is a summary of details regarding the fungus. Three 

 kinds of spores are produced : microconidia, macroconidia, and chlamydo- 

 spores. 



Microconidia are thus produced : The end of a long hypha, or a lateral 

 branch, is cut off from the remaining portion by a wide constriction 

 furrow. As soon as one of these microconidia is cut off, the hypha begins 

 to elongate, which continues until the point has advanced even to the 

 further end of the first conidium ; but even before this growth is complete 

 a similar constriction furrow begins to cut off a second conidium. This 

 process continues until sometimes six or eight microconidia are formed 

 from one branch and lie side by side in a little group. These microconidia 

 are oval or elliptical, thin- walled, one- celled, uninucleate, and slightly 

 curved. They vary in length from 5^ to 16 n and in diameter from 

 2 /j to 2^ p, the most common size being about 91 x 3 p. These conidia 

 were observed to germinate in distilled water in from six to eight hours. 



