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The Museum Gazette 



extent and it should be carefully guarded against by efficient 

 " earthing." It is, however, not likely that it accounts for 

 much of what occurs, and either inheritance from the parent 

 "sets" or air-infection are in all probability by very far the 

 most common causes of loss of the crop. The rapidity with 

 which in damp weather the disease may spread over a large 

 field is tolerably conclusive evidence of aerial convection. It 

 is possible, even perhaps probable, that the disease may take 

 its beginning every year in any given district from infected 

 " sets," but when once it has been developed there can be no 

 doubt that the zoospores given off by the leaves are the cause 

 of its prevalence. 



The possibility of infection from diseased " sets" has long 

 been assumed. It has recently been demonstrated by some 

 interesting experiments conducted by Mr. George Massee, 

 F.L.S. In an article in the Kew Bulletin (No. 4, 1906), 

 Mr. Massee has detailed experiments which conclusively 

 prove that hybernating mycelium in a tuber is capable, under 

 favourable conditions, of perpetuating the disease. 



" Three diseased potato tubers, showing rusty stains 

 characteristic of the presence of Phytophthora mycelium in 

 the flesh, were each cut into two equal parts. Each half- 

 tuber was planted separately in a plant-pot ; the same kind 

 of soil and manure, sterilised by steam, was used in all the 

 experiments. Three of the pots were placed in a house 

 having a temperature ranging between 70 0 and 8o° F., in 

 dull light, and with the moisture often at saturation point. 

 Each pot was placed under a bell-jar. The three remain- 

 ing pots were placed in a well-lighted house, without any 

 artificial heat, and with an exceptionally dry atmosphere. 

 These pots were not placed under bell-jars. An equal 

 amount of water was supplied to each of the six pots. 

 The three plants grown under conditions of high tempera- 

 ture, dull light, and much moisture in the air, showed the 

 first indication of Phytophthora when shoots were six weeks 

 old, and a fortnight later the three plants were blackened 

 and destroyed by the fungus. 



" The three plants grown in the cool, well-lighted, dry house, 

 showed no trace of disease at the end of two months, when 

 one of the plants was removed and placed under a bell-jar. 

 Within nine days this plant was blackened and killed by the 



