164 "Damping off," etc., of Tomato Seedlings 



following experiments were made. Seeds were sown in infected soils in 

 thickness varying from 600 to 25 seeds per box, in sets of four boxes at 

 each degree of thickness. In half the boxes the seedlings were removed, 

 as they were attacked, to eliminate the factor of spread. The remainder 

 were untouched and gave some indication as to the rate of superficial 

 spread of the fungus. The results obtained are shown in Table III. 



Table III. 



No. of seeds Average % diseased seedlings Average % diseased seedlings 

 per box removed when attacked not removed 



600 51 100 



300 45 100 



200 49 100 



100 42 78 



50 37 46 



25 35 41 



The second column of the above table shows the uniform results 

 obtained when the seedlings were removed as they were attacked. It 

 indicates that the number of seedlings primarily attacked depends upon 

 the number of disease centres in the soil and not upon the closeness of 

 sowing, when the factor of superficial spread of the organisms is eliminated. 

 The third column where the fungi were allowed to spread is of great 

 practical interest, and shows that the rate of spread of the organism is 

 more rapid, where the seeds are closely sown, than where they are thinly 

 sown. In the closer sowings the density of the plants increases the film 

 of water adhering to the seedlings and offers a ready means of spreading 

 the disease through the box. 



Sowing above fifty to the box should be avoided as this materially 

 assists the disease. 



The relation of the time and method of watering to the incidence of the disease. 



Boxes were "made up" in the usual way, using 5 lbs. of infected soil 

 from the stock heap, sowing 100 seeds per box and removing the seedlings 

 as they became diseased. As soon as the seedlings appeared, the glass 

 covers were removed and the different methods of watering were com- 

 menced. For top watering in the morning, midday and evening, 200 c.c. 

 of sterile water were given to each box on every alternate day. For 

 bottom watering the boxes were placed for five minutes each in a zinc 

 tray filled half an inch deep with water. One set of boxes was placed on 

 damp earth in a tray on the staging and received no direct watering after 

 their first soaking preparatory to sowing. The soil upon which they rested 



