64 



of micro-organisms is low and its vital activities greatly reduced. In this 

 condition the resistance of the organism to chemical agents is extremely 

 high. In the presence of atmospheric moisture the protoplasm rapidly 

 absorbs water, its vital activity, as we have already noted, rapidly increases, 

 and it becomes extremely sensitive to the destructive agent. In fumigation 

 to destroy disease germs we must maintain a high humidity for effective 

 destruction; conversely, in the fumigation of seed infested with insect life 

 the water content of the seed must not be too high if we wish to preserve 

 its germinative power. 



HIGH TEMPERATURES KILL DISEASES. 



Treatment of seed to high temperatures has recently been advocated' for 

 the killing of disease organisms that infest it. This treatment, if effective, 

 depends on the difference in resistance of host and parasite to high tem- 

 peratures. It is one, I am certain, in which the water relation must receive 

 careful attention if the germinative power and seedling vigor is to be pre- 

 served. Waggoner in a series of careful experiments on radish seeds found 

 that with an initial water content of 45 per cent and above, all seeds are 

 killed at 140 F. If the water content of the seed' be decreased before its 

 subjection to the higher temperature, the per cent of germination is in- 

 creased, that is, the death point is shifted higher. For example, a change 

 in the water content of a sample from 45 to 30 per cent shifts the death point 

 from 140F to 149F. Air-dry seeds of approximately four per cent water 

 content, germinate normally after heating to 167F for half an hour, and are 

 killed between 204F and 212F. Seeds from similar samples carefully dried 

 until only four-tenths of one per cent of water is present at the time of treat- 

 ment, give a normal germination after treatment at 212 F, and are killed 

 between 253.4 and 257F. We find' that as the water content increases from 

 four-tenths of one per cent to 45 per cent the maximum temperature at which 

 a normal per cent of germination takes place, drops from 212F to below 

 122F, and the lethal temperature falls from between 253.4-257F to 

 122-140 F. 



It is to be observed, however, that exposure to higher temperatures 

 retards germination, and, in seeds of medium water content, affects the 

 vigor of the seedling. The retardation in the germination of radish seed 

 differing in water content when heated at 176 F. for thirty minutes, follows: 



Water content of seeds when heated. 4% 9% 14% 18% Check in 



treatment 



Per cent germinating 1st day 6 0.6 0. 0. 30 



Per cent germinating 2d day 21 5.4 0. 0. 45 



Per cent germinating 3d day 35 17.0 7.4 0. 14 



Per. cent germinating 4th day 17 24.2 11.0 0. 3 



Per cent germinating 5th day 3 10.0 6.0 0. 2 



Per cent germinating 6th day 1 3.6 2.2 0. 1 



Per cent germinating 7th day 0. .4 0. 



Total per cent germinating 83 60.8 27.0 0. 95 



The difference in injury resulting from treatment to temperatures below 

 freezing of soaked and dry grains is of interest. The following varieties 

 of wheat: Illinois No. 1, spring bearded; Marquis, spring smooth; Dawson's 

 Golden Chaff, winter bearded; Turkey Red, winter bearded, and Red Cross, 

 winter smooth, in dry and swollen conditions, were treated for different 

 intervals of time to a temperature of 10F. 



The air-dry grain subjected' for ninety hours to a temperature of 10F 

 and then placed in the germinator at 59F germinates Illinois No. 1 93%, 

 Marquis 89%, Red Cross 85%, Dawson's Golden Chaff 71%, Turkey Red 93%. 

 (These figures are slightly below the germination of the untreated samples.) 

 Similar samples soaked in water for six hours and then exposed for seventy- 

 five hours to a temperature of 10 F germinate Illinois No. 1 25%, Marquis 

 10%, Dawson's Golden Chaff 1%, Turkey Red 3%, Red Cross 4%. The same 

 varieties soaked in water for three hours and then exposed to a temperature 

 of 10.4 F. for forty hours, show a markedly decreased germination. Our re- 

 sults as a whole show a marked difference in resistance to low temperatures, 

 especially when the water content of the seed is high. The ability to with- 



