74 The Ohio Journal of Science [Vol. XX, No. 3, 



the wind intervals show that the mullein leaves offer less 

 resistance to water loss in wind than in still air. A summary 

 of these comparisons gives the following conclusions: 



1. Mullein leaves offer a greater resistance to water loss in 

 darkness than in light when compared with tobacco leaves. 



2. Mullein leaves offer less resistance to water loss in wind 

 than in still air when compared with tobacco leaves. 



3. Mullein leaves respond as much or more to changes in 

 the environment than tobacco leaves. 



The ratios of sub-series-a in series II are taken as standard 

 for comparing the other ratios of the series, because all plants 

 are normal. The total ratios for the three experiments are 

 compared in each sub-series. The two standard ratios are 

 ( = 0.98) and ) = 0.82) their difference being due to the differences 

 in transpiration rates of equal leaf areas of several plants of the 

 same species even under identical conditions. These ratios, 

 when the hairs are removed from the plants, become ( = 0.99) and 

 ( = 0.83) which shows that the removal of the hair does not alter 

 the resistance of the leaves to water loss. When the ratios of the 

 same plants in wind and light with the hair removed are found 

 ( = 0.91) and ( = 0.78) we see that the removal of the hairs has 

 slightly decreased the resistance of the leaves to water loss in 

 wind when compared with still air. This difference is due to 

 the fact that a larger cuticular surface is exposed to the 

 evaporating powers of the air when the hairs are removed, and 

 that wind increases water loss from this exposed surface more 

 than the usual rate in still air. This difference, however, is 

 very slight as compared with the internal surface of the leaf. 

 When the plants are placed in a darkroom and the ratios of 

 the results obtained there are compared ( = 0.56) and ( = 0.65) 

 there is a great difference noticed. The effect of removing the 

 hairs from the leaves is to greatly increase the resistance in 

 darkness as compared with plants having hairs in light. This 

 increase, however, is caused by the increased transpiration, 

 which in darkness is cuticular because the stomata are closed, 

 and is much larger because a greater surface is exposed to the 

 evaporating power of the air. Series II, therefore, warrants 

 the following conclusions: 



4. The removal of the hairs from the mullein leaves does 

 not alter the resistance of the leaves to water loss in still air 

 and light. 



