DIVISION' OF BOTANY 835 



SESSIONAL PAPER No. 16 



of the silvered spot or those forming the sclerotium grow out from the surface of the 

 tuber and bear the s^res in groups along them, being more or less treelike in appear- 

 ance. Each spore is of a dark -brown colour and consists of a row of cells. If placed 

 in water during the summer months the spores germinate readily inside two days, and 

 form a germ-tube several times the length of the spore itself. When tubers showing 

 Silver Scurf are planted in the ground, doubtless spores are formed and germinate 

 in a similar manner, and in this way the infection probably spreads to the next crop 

 of potatoes. 



The tree-like spore-bearing stage of this fungus was described by Harz as Spondy- 

 Jocladium atrovirens, while the sclerotium form Avas described by Frank __as Phellomyces 

 sclerotiophorus. Later, Appel and Laubert showed that they were both different 

 stages of the same fungus, consequently the former name is the one by which the 

 fungus is now known. 



Orton, in Farmers' Bulletin No. 544 of the United States Department of Agri- 

 culture, published in 1913, states that the disease has recently been introduced from 

 Europe and is spreading rapidly in the Eastern States. Melhus, in Circular No. 127, 

 Bureau of Plant Industry, dated 1913, says that the fvmgus is not killed by seed dis- 

 infection with formalin or corrosive sublimate. On the other hand, Johnson, of 

 Dublin, found that soaking the tubers for one hour in a solution of formalin of rather 

 less than one per cent strength was an effective remedy. 



Experiments showing the results of steeping affected tubers in various fungicides 

 are being carried out at the Central Experimental Farm, but the results will not be 

 available until the autumn of the year 1914. In the meantime, farmers would be wise 

 to reject seed-tubers affected with this malady. Although the disease has not up to 

 the present been regarded as a very serious one, still as it kills the outer cells of the 

 skin of the tuber, and as these outer cells are the most important part of the skin in 

 preventing the entrance of fungal diseases, it is just possible that it may prepare the 

 way for other more serious maladies. 



The accompanying plate shows the external appearance of the disease on the 

 surface of the potato tuber. 



" Black Heart " of Potatoes (See plate I). — Mr. E. T. Bartholomew, in Phytopath- 

 ology III, p. 180 describes and figures a blackish discolouration in the centre of pota- 

 toes which is quite different from the " sprain " or " internal brown streak " or the 

 " rusty spots " which are being observed from time to time. He publishes a prelim- 

 inary note in which he states that this often purplish to inky-black spot, at times show- 

 ing a central cavity, may be prodiiced in potatoes that have been stored during winter 

 by keeping them for a certain period of time in a temperature of about 40° C 

 (104^ F.). 



We have had occasion to observe the identical trouble this spring. For experi- 

 mental purposes, the following varieties were stored in a " pit " above ground at some 

 rather exposed place at the Central Farm on November 1, 1913: Irish Cobbler, Gold 

 Coin, Early Delaware, Carman No. 1. The outside temperature went down to some 

 30° F. below zero. The temperature of the pit was taken daily by a self -registering 

 thermometer. During no time was the temperature recorded below 32-5° or above 

 46-5° F. Thermometer and recorder were both reliable. 



The same varieties of potatoes were stored in the farm root-house where at no 

 time did the temperature rise above 45° F. or go down to freezing. 



A third lot was stored in the cellar of a heated barn where the temperature went 

 little above 42 °F. 



Good ventilation existed in all three places of storage. ^ 



In April, 1914, the pit was opened and showed that frost had no doubt invaded 

 the pit, the upper layer of potatoes shnwod plain signs of the wet and pulpy spots due 



Ott.\wa. 



