GOOSEBERRY-MILDEW AND GOOSEBERRY CULTIVATION. 47 J 



fungus. In the following summer — at Stockholm from the middle to 

 the end of July — the disease has again appeared on the new shoots, which 

 up to that time had been apparently healthy, and within a short time — 

 one or two weeks at most — it has been found seriously attacking the 

 whole plantation. 



A telling instance is given by a grower in South Sweden. In a letter 

 of June 23, 1908, he writes as follows : " In 1905 I ordered from a 

 nursery at Stockholm a hundred gooseberry bushes of different varieties 

 for the purpose of planting in a garden where gooseberry bushes had 

 never been cultivated before. The next summer I had the mildew on 

 every plant. Then I cut all the bushes to the ground, and sprayed the 

 tops of the shoots as well as the ground with a solution of potassium 

 sulphide and lime-wash ; I repeated this treatment in the autumn of 

 the same year, as well as in the spring and autumn of 1907. It is true 

 that some plants died, but the bushes that were left appeared, relatively, 

 vigorous. These were sprayed thoroughly last spring, 1908, with a strong 

 solution of bluestone (copper sulphate), lime, and imperial green. In 

 spite of these energetic measures every bush shows at this moment, and 

 has shown for the last two weeks, the disease in its most marked form. 

 And what is especially sad is that I have, in the immediate neigh- 

 bourhood, another garden with a large number of older gooseberry bushes, 

 and here, too, the disease has now appeared, thus endangering the 

 cultivation of the gooseberry in the whole district, where the mildew has 

 hitherto been unknown." 



It may be added that the above-mentioned plants came from a nursery 

 which I had examined in the autumn of 1905, without being able to 

 discover a single trace of the disease. 



11. Is the Disease Internal in the Gooseberry -plant ? It is a 

 common idea that this mildew, like all other kinds of mildew, is confined 

 to the surface only of the plant attacked, and that it lives so superficially 

 on it that the mycelium does not penetrate into the interior of the tissue, 

 but only sends minute suckers (haustoria) into the epidermis-cells, which 

 are poor in nutritious substances. This theory, however, scarcely explains 

 how the fungus is capable not only of rapidly and thoroughly covering 

 the surface of the attacked organ with a cobweb overgrowth, but also of 

 causing great damage to the organ itself, and even of destroying it com- 

 pletely. 



This theory is insufficient to explain the numerous experiences gained 

 during the last few years concerning the gooseberry-mildew. I cannot, 

 therefore, but suppose that the fungus is able to live — perhaps in a form 

 very difficult of recognition — within the diseased shoot itself, and to 

 thoroughly infect the interior of it. At the end of the period of 

 vegetation, late in the autumn, a sap thus poisoned is diffused down 

 through the stock and the root. In the following season this sap- 

 stream rises again in the plant, and causes in a few days a new outbreak 

 of the disease. 



That such an internal symbiosis through the whole plant really 

 exists in corn-plants, seriously attacked by different kinds of rust, is a 

 matter that nowadays can hardly be disputed, even though some links 

 in the chain of evidence are still wanting. 



