Sept. 1896.] ROTTENNESS OF TURNIPS AND SWEDES. 



125 



I have observed numerous tufts of grey mould, which proved 

 to be a Botrytis, and also black patches of irregular shape 

 (Fig. 11) both upon the decorticated haulm and in the central 

 hollow of the stem. The black patches are the sclerotia of a 

 fungus seemingly identical with the one described by Worth- 

 ington Smith, under the name of Peziza postuma, as a "■ New 

 disease of potatoes " which had appeared in Ireland and near 

 Aberdeen. This disease is also described by Professor A. Blytt 

 as being very destructive in Norway, near Stavanger. Accord- 

 ing to de Bary, the disease appears upon the foliage shoots 

 soon after flowering, the fungus being identical with Peziza 

 sclerotiorum. 



The sclerotia are very common in this neighbourhood upon 

 the dead potato haulms. When placed in a damp atmosphere, 

 as, for instance, in a test-tube with a little water at the base 

 and plugged at the top, they readily germinate in the course of 

 three or more days, according to the temperature, producing 

 conidiophores and conidia precisely similar to those described 

 upon the decaying swedes and their sclerotia (Figs. 12 and 13). 

 As far as my observations go, the sclerotia always give rise to 

 conidia, and never to a Peziza* The sclerotia, again, will 

 germinate when buried in the ground ; a flower-pot nearly filled 

 with earth was taken and a number of sclerotia still attached to 

 the potato-haulms were buried in it, the pot being then well 

 watered and kept under a bell-jar. After a few days a number 

 of conidiophores with conidia appeared above the surface of the 

 soil, being gradually followed by others as they were able to 

 make their way to the surface. 



Considering that the conidia on the potato-haulms are espe- 

 cially to be found when the swedes are being pulled, topped and 

 tailed, and led to the pits, it is a matter of some economic im- 

 portance to determine whether these conidia can infect the 

 swedes. This I have found to be the case ; the conidia from 

 the sclerotia upon the potato-haulms, when sown with all 

 possible precautions to prevent the admixture of other conidia 

 or spores, upon pieces of turnip and swede, germinated, the sub- 

 stratum became discoloured and rotten, and covered with hyphse, 

 while conidiophores, and subsequently sclerotia, were developed. 

 There can be no doubt, therefore, that the fungus which 

 causes so much destruction in the swede pits is identical with 

 that which produces the sclerotia upon the potato-haulms, and 

 without wishing to preclude the possibility of the conidia being 

 derived from other sources, it may be insisted upon that the 

 potato-haulms forming a nidus for this fungus are a source of 

 danger to the swedes. 



A great many important facts have been elicited with regard 

 to the conditions under which Botrytis can gain an entrance 

 into its host. The species of Botrytis have been more usually 



* Other observers, notably Worthington Smith and Axel Blytt, only record a 

 peziza-stage. 



