8 



of the fungus. In the final stages of the disease the outer portion 

 of the stem becomes affected and rots away. 



All this may readily be seen with the microscope. The important 

 question now arises, where does this fungus come from and how 

 does it attack the plant ? The solution of this point underlies the 

 whole problem of preventing or treating the disease. A particular 

 case may be described. In the spring of 1900 we planted a large 

 amount of aster seed in flats in a greenhouse. The seed was planted 

 quite thickly so that the plants after coming up stood very close 

 together in the rows. A long period of wet cloudy weather followed 

 and soon the trouble known as "damping oft" set in quite abund- 

 antly. The affected seedlings did not die suddenly, but would wilt 

 down and gradually wither away. Examination showed that the 

 base of the stem and roots had rotted off. As soon as possible the 

 plants were pricked out, saving only the best. Many more rotted 

 off after this, so that when the permanent beds were set out on June 

 8 many varieties were very poorly represented. It was noticeable in 

 the flats that many plants showed a trouble, evidently a continuation 

 of the damping off in the seed bed, which resembled in every way 

 the wilt of older plants just described, except that being younger 

 and more tender the stem rotted off more quickly. This rotting 

 affected first the woody tissue as in the typical disease. Plants in 

 the flats were continually wilting and dying in this way. In many 

 cases, however, an apparent recovery took place. In some lots of 

 badly affected seedlings almost every piant showed at the time of 

 pricking out a small dark spot on the stem, from which the rotting 

 proceeded. In those which appeared to recover a callous tissue 

 grew over this spot, becoming a sort of scab and appearing to check 

 the decay of the stem. By carefully following individual plants it 

 was found that these were the plants which showed the wilt disease 

 after being set out. The fungus in all these cases was the same. 

 This is an important point, namely, that the disease was amtracted in 

 the seed bed as a result of conditiims which favor damping off. 



Acting upon this idea comparisons were constantly made between 

 plants started in the greenhouse which damped off more or less and 

 those which were started in the open ground and kept in vigorous 

 growth from the first. The development of individual plants and 

 typical lots of plants, affected and unaffected, was carefully followed 

 up, with the result that in every case where plants died from stem 



