20 THE COTTON PLANT IN EGYPT CHAP. 



most serious attack is the inconspicuous one which occurs 

 at the beginning of germination. 



A treatment of the seed with 2J per cent, of its weight 

 of naphthalene, mixed with gypsum as a cement, effec- 

 tually prevents this primary attack, though leaving the 

 seedling unprotected by. the time of secondary infection. 



A notable example of secondary infection was observed 

 in May, 1906, on a piece of land at Giza, which had 

 become very foul with weeds, and was consequently a hot- 

 bed of " sore-shin," so that a third sowing had been 

 necessary. The clusters of seedlings from this were 

 perfectly clean, under the protection of the summer 

 temperature, till two abnormally cool and cloudy days 

 arrived. When these were over, every tenth cluster had 

 been completely destroyed, 6 and the clean white roots had 

 deliquesced into a sodden brown mass. 



The facts here related led the author to a conviction 

 that furthur investigation would be profitable, and after 

 some experimental difficulty, a method for studying the 

 relation of this fungus to temperature was devised. Since 

 the results appear to be capable of general application, 

 their description may be considered under a general title, 

 and supplemented by less precise data from cotton itself. 



Temperature and growth. 9 The effects of tem- 

 perature on the growth of the " sore-shin " fungus were 

 studied with special apparatus. A moist-chamber was 

 devised in which the concentration of the "hanging drop " 

 containing the fungus remained constant, however quickly 

 the temperature was changed. This change was effected 

 through a double jacket of liquid in which the chamber 

 was completely immersed. The measurements of elonga- 

 tion of the observed hypha were made every minute 

 through a water-immersion objective with a micrometer 

 eyepiece, while the actual temperature of the hanging-di'op 

 itself was recorded to 0'1 C. by means of a delicate 

 thermo-electric junction in the field of the microscope, 



