128 



ROTTENNESS OF TURNIPS AND SWEDES. [Sept. 1896. 



On the swede in the three tubes (a, b, c) upon which eonidia 

 had been sown previous to freezing, a mycelium was very soon 

 found to be growing ; this mycelium developed very copiously, 

 filling up the test-tube in the neighbourhood of the piece of 

 swede. By the end of 10 days both eonidia and sclerotia were 

 produced. A similar development was found on the three pieces 

 of swede which had been sown with frozen eonidia (d, e,f). On 

 the three (g, h, i) which were sown with unfrozen eonidia the 

 development of the mycelium proceeded more slowly. To 

 further test the power the eonidia have of resisting severe frost, 

 several of the eonidia frozen in the test-tubes were sown in a 

 hanging drop ; all germinated and produced a short hypha, but 

 since they were sown in water only their further development 

 could not proceed. . 



This experiment shows that the activity of the eonidia is not 

 affected by the frost, and that they can retain their vitality 

 after being subjected to an extremely low temperature, and 

 afterwards may develop a mycelium which can live as a sapro- 

 phyte upon the frozen roots. Although no actual measurements 

 were made, yet the growth of the mycelium was distinctly more 

 vigorous upon the pieces of frozen swede than upon those which 

 were unfrozen, indicating that this fungus develops more rapidly 

 as a saprophyte than as a parasite. 



In very severe weather the effect of the frost is to kill and 

 rot the roots, which might also prepare the way for the Botrytis, 

 but it has been shown that the fungus attacks and destroys the 

 root quite independently of anjr action of the frost, and this is 

 further borne out by the prevalence of the disease after the late 

 very mild winter. 



Means of Checking the Ravages of Botrytis. 



In order to check the ravages of this fungus we must seek some 

 way of entirely destroying it. Naturally the most feasible and 

 effective means would be to ensure the destruction of the 

 sclerotia, and hence it is evident that all decaying potato-haulms 

 and decaying roots, as well as the swede and turnip tops, 

 together with rotting vegetable matter generally, should be 

 burnt as scon as possible. Merely burying the decaying mate- 

 rial (unless it might be at a considerable depth) is of little avail, 

 for, as has been shown in an experiment previously mentioned, 

 the sclerotia when buried germinated freely, producing tufts of 

 eonidia above the soil. How often do we find not only turnip- 

 tops, &c, but the rotten and discarded roots lying in heaps or 

 scattered on the fields, ready in the spring to produce a brood 

 of eonidia. And, in this connexion, it may be observed, that 

 the Botrytis does not confine its ravages to roots and potato- 

 haulms : — Kissling has traced an epidemic on Gentiana lutea in 

 the Jura, and also the decay of chestnuts in cellars to this 

 fungus ; Zimmerman has shown how it attacks many plants in 

 greenhouses, especially in winter, the eonidia from decaying 



