I30 



Journal of Agriciiliural Research 



Vol. VI, No. 3 



was covered with glass during the night and was only opened during 

 the warmer part of the day. The plants appeared perfectly healthy at 

 all times and grew well. 



Other plantings were made in the laboratory yard at intervals during 

 March for studies under outside conditions. Later, seeds were germi- 

 nated between layers of moist absorbent cotton and placed in pots con- 

 taining soil sterilized by baking. These pots were then placed in large 

 screen cages and the plants were allowed to grow under this protection. 



The first injury was noted in the hotbed on March 31. These seedlings 

 had sprouted March 1 6 and at this time were about 3 inches tall. They 

 had been protected from cold by the glass covers, and the soil had been 

 well manured. On this first morning a number of plants were found to 

 have been injured. 



Following this the progress of the injury was noted carefully. All 

 plants were examined daily and those showing injury were tagged. In 

 this manner a record of the number of plants injured each day was 

 secured. On the morning of April 14 nine new seedlings were injured; 

 on April 1 5 five, on April 1 6 six, on April 1 7 two, and on April 1 8 three. 



In order to determine the period in which the injury was incurred, 

 both morning and evening counts were started. These showed the num- 

 ber of seedlings injured during the night and during the day. These 

 observations were started April 22 and continued until May 4. The 

 results are presented in Table I. 



Table I. — Comparison of day and night injury to cotton seedlings 



Date of examination . 



Apr. 22. 



23- 

 26. 

 27. 

 28. 

 29. 

 30- 



Number 

 of seed- 

 lings 

 injured 

 during 

 day. 



Number 

 of seed- 

 lings 

 injured 

 during 

 night. 



Date of examination. 



May I 



2 



3 



4 



Total 



Number 

 of seed- 

 lings 

 injured 

 during 

 day. 



26 



Number 

 of seed- 

 lings 

 injured 

 during 

 night. 



49 



From this table it is seen that 66 per cent of the injury appeared 

 during the night and 34 per cent during the day. 



On April 14 this same type of injury appeared upon seedlings which 

 had just sprouted in the laboratory garden, and from that time it appeared 

 about as abundantly here as in the hotbed. 



The rapidity with which the injury was produced was quite striking, 

 and special studies were made upon this point. A number of appar- 

 ently healthy and entire seedlings were examined morning and evening, 

 and in that way the amount of injury produced in a single night was 



