/r 



keep :;he temperature below the death point. 



interesting results were obtained in an experiment to dis- 



#6^4+ 

 cover the weakest stimulus whicu would produce the charact4ristic 



A 



orientations of natural illumination. Cultures were placed at in- 

 tervals of 15 cm. froia an east window a^n exposed 8 hours on a 

 cloudy day> Upon examination a few days later every culture was-te 



found to show strikingly the strong orienting effect of unilateral 

 in 



daylight. Even the one fartherest away, 350 cm. from the window^ were 

 practically all oriented 



c^~4j,* "l^more'dfr lets^/ 

 r ._ivery Culture js nowing this orientaion has.f requent ex- 



ceptions to the rule. Every worker on this problem has reported 

 such exfceptiens and they toave been ex*~plained by the assumption 

 of the existence of an inherent polarity which as a rule i over- 

 come by the stronger light stimulus. The fact that in absolute -fr 

 darkness, germination and normal growth are as rapid or more so 

 than in light, also points 60 an inherent polarity. But the tend- 

 ancy varies enormously in individual spores. Therefore it is easy 

 to understand that slight variations in the quantity and quality of 

 illumination might easily produce'-b*^ changes in the ] sensitiveness 

 of the spore toward light, which ;eans failure of experiments with 

 monochromatic light until the right combination of other external 

 factors in produced. 



It was^oon discovered in the course of this investigation 

 that although the WJLtf intensity of the electric are. used was too 

 low to orient the cleavage plane of the egg and too low to cause 

 the cell away from the ligh , to become the rhizoidal cell, it was 

 strong enough to produce a conspicuous neeative heliotropism of the 

 rhizoids of these same spores if the illumination was resumed after 

 the rhizoids fead develop d- OKly seven hour exposures were used to 



