124 



ROTTENNESS OF TURNIPS AND SWEDES. [Sept. 1896. 



conidia, the lower portion being of a light brown colour, the 

 upper, where the conidia are produced, white. The development 

 of the conidia proceeds for some time with great rapidity, and 

 towards the close of production of the conidia the hyphae imme- 

 diately below the surface of the turnip, or sometimes upon the 

 surface, are aggregated into the small black masses previously 

 described as sclerotia. 



So far we have seen that Botrytis can be readily cultivated 

 in test-tubes upon pieces of fresh turnip or swede as a laboratory 

 experiment, but it remains to be shown whether the fungus can 

 flourish as a parasite on actually living plants in the field. 

 Selecting certain sound and healthy turnips grown specially in 

 the College Botanical Garden, a small conical piece was removed 

 from one side of each "bulb," and conidia sown upon the freshly 

 cut surface, the piece being then quickly replaced. On exami- 

 nation after a week or ten days the surface in some cases had 

 turned brown, and the turnip when pressed was found to be soft 

 in the interior. In a short time conidiophores bearing conidia 

 might be observed upon the cut surface, and also emerging from 

 the uninjured parts bordering upon the cut. When cut open 

 these turnips were found to be more or less decayed and brown 

 in the interior, the discolouration advancing from the spot where 

 the conidia had been sown. Other plants, after being allowed 

 to grow for a longer period, say three weeks, when examined 

 showed a much more extended decay, the disease having spread 

 almost throughout the entire " bulb." The Figure 10 represents 

 a drawing of a white globe turnip in an advanced stage of 

 decay, infected with conidia on September 20th, and removed 

 from the garden on October 11th. It was cut open and the 

 drawing made on the same day. On microscopical examination 

 the discoloured portion was found pervaded by hyphse ; in the 

 course of a few days the exposed surface was covered with 

 numerous conidiophores bearing conidia, the mycelium having 

 in the meantime extended over the only remaining sound part ; 

 sclerotia also were developed subsequently. To further demon- 

 strate that these hyphse really belonged to the Botrytis, a series 

 of six sterile tubes were prepared, and into each of these pieces 

 cut with a sterilized knife from one of the infected turnips in 

 the garden were introduced. The pieces selected showed a 

 larger or smaller amount of disease, one having only a few 

 brown cells. In every instance the discolouration spread 

 throughout the entire piece, and numerous conidiophores, and 

 afterwards sclerotia characteristic of the Botrytis, were developed 

 as before. 



These experiments have fully proved that the Botrytis lives 

 as a parasite upon turnips and creates great havoc among the 

 roots in the pits ; but, as I shall presently show, this fungus 

 attacks the potato also, and may be directly spread from one to 

 the other. 



Upon the dead and decaying potato haulms and leaves 

 which are left in the fields when the potatoes have been dug up, 



