196 PROBLEMS OF GENETICS 



difference of even three weeks in time of harvesting may easily 

 be due to variation in the season. It would in any case be dif- 

 ficult to analyse the meteorological conditions, and to decide how 

 much effect in postponing or accelerating the harvest might be 

 due to cold days, to cloudy days, to wet weather, to fluctuations 

 in average temperature, to hot days, and other such incidents 

 occurring at the different periods of growth, even if they were 

 specially watched while the experiments were in progress, and 

 at this distance of time such analysis is practically impossible. 

 Without careful simultaneous control-experiments this evi- 

 dence is almost worthless. The director of the Meteorological 

 Office 7 has, however, kindly sent me some details of the weather 

 at Breslau from 1857 to i860, and I notice that as a matter of 

 fact July, 1859, was an exceptionally hot month, having an average 

 of 2.67 C. above the mean for the twenty years 1 848-1 867. June 

 in that year was slightly (0.3 1° C.) below the mean and May 

 slightly above it (0.18 C). August was also abnormally hot, 

 2. 35 C. above the average. The Breslau wheat was sown on 

 May iq and harvested on August 6. There was a cold spell from 

 May 11 to 14, which this wheat escaped, as it was sown on May 

 19. In the other years the cold spell came much later. These 

 elements of the weather may possibly have done something to 

 iiurry the ripening in 1859. It is unfortunate that we are not 

 told how long similar wheat from Breslau seed took to ripen in 

 that year. 



As regards the Norway cultivations we have the average 

 monthly temperatures recorded by Schiibeler, though he does 

 not discuss them in connection with this special problem. It is 

 quite clear that 1857, in which the period was 103 days, was an 

 •exceptionally cold summer, especially as regards the months of 

 June and July, but though there was, so far as the temperature 



7 1 am obliged to him and to Dr. E. Gold for much trouble taken to answer 

 my questions. Some idea of the kind of weather indicated by an average of 2.67 

 C. above the mean may be got from a comparison with the year 191 1, which most 

 people will remember as one of the hottest summers they have known. The 

 July of that year was in east and southeast England about 4 F. above the mean 

 but 2.67 C. means about 4.8 F. above the mean. At Greenwich July, 1859, was 

 about 6. 5 F. above the average. 



