1892.] PUBLIC DOCUMENT — No. 33. 219 



The Rotting of Lettuce. — Botrytis vulgaris Fr.* 

 Gardeners who cultivate lettuce as a winter crop usually 

 suffer somewhat and often lose extensively by the rottino- of 

 the plant while still only partially grown. The trouble or- 

 dinarily appears first upon the stem of the plant, about at 

 the surface of the soil. Here may be seen at first a soft, 

 dark, decayed spot, which rapidly spreads, penetrating the 

 stem and involving next the bases of the lower leaves. The 

 latter, being thus cut off from the plant by the decay of 

 their bases, usually dry up. With the further progress of 

 the decay, the centre of the head, with the tender inner 

 leaves, becomes attacked, and soon collapses into a fetid, 

 slimy mass. In the decaying tissues one can often recognize 

 fungus threads ; and, if they are left undisturbed, there 

 appear on the decayed remains the fruiting threads and 

 spores of a fungus, always the same. When portions of 

 the attacked tissues are removed and placed in a moist 

 chamber after being thoroughly washed, I have found that 

 the same fungus develops promptly and abundantly, and is 

 never accompanied by any other. The study of specimens 

 from various sources has led always to the same result. 



Infection experiments with the fungus on healthy plants 

 have been attended with little success; but the most that 

 can be said is that their results indicate that the fungus 

 requires for its attack conditions not yet determined. They 

 do not negative the very strong evidence furnished by the 

 constant association of the fungus with the decay. These 

 experiments have not been carried so far as is desirable, on 

 account of a lack of sufficient suitable material, and further 

 cultures which I hope to make this winter may show that 

 we have here a case similar to that described by DeBary,| 

 in which the fungus threads require to be nourished sapro- 

 phytically for a time before they can gain sufficient vigor to 

 enable them to attack and live parasitically upon their host. 

 The fungus in question is one of the imperfect forms 

 known as Botrytis or Polyactis, and agrees in many respects 



* Two plates which had been prepared to illustrate the first two articles of this 

 report, and delivered to the lithographer, were unaccountably lost in the mail before 

 their engraving had been completed. It was impossible to duplicate the drawings in 

 season for this report, but they will be prepared and published as soon as practicable 



t Botan. Zeitung, 1886, Nos. 22-27. 



