^66 Dr. H. Franklin Parsons on 



rootlets which are the means of nutrition of the plant. For a 

 similar reason plants which are well rooted will bear a frost 

 which would kill those which have been recently transplanted, 

 the rootlets of the former having penetrated to a sufficient depth 

 to be out of harm's way. 



The seasonal growth of plants, and especially of bulbous and 

 other plants which send up annual stems from perennial roots, 

 is doubtless largely dependent upon the temperature of the soil, 

 probably as much as upon direct solar heat or air temperature. 

 With most of our indigenous plants probably growth does not 

 commence until a temperature of about 42° F. has been reached. 

 This is a direction in which much useful knowledge is likely to be 

 gained by a combination of phenological and earth temperature 

 observations. 



The combination in autumn of moisture and plentiful decaying 

 organic matter, with a high ground temperature, is probably the 

 cause of the abundant development of fungi at that season in 

 our woods and fields. Similar causes probably account for the 

 seasonal prevalence in autumn of certain diseases, as typhoid 

 fever and diphtheria, which are believed to be produced by bacteria 

 of kinds capable of living outside the human body as well as within 

 it. In at least one disease, viz., the epidemic diarrhoea, which 

 occasions such a heavy mortality among children in some of our 

 large towns, a definite connection with earth temperature con- 

 ditions has Ijeen made out. On this point my former colleague, 

 Dr. Ballard, says : — " The summer rise of diarrhoea mortality 

 does not commence until the mean temperature recorded by the 

 4 ft. earth thermometer has attained somewhere about 56" F., no 

 matter what may have been the temperature previously attained 

 by the atmosphere or recorded by the 1 ft. earth thermometer. 

 The maximum diarrhoea mortality of the year is usually observed 

 in the week in which the temperature recorded by the 4 ft. earth 

 thermometer attains its mean weekly maximum. The decline of 

 the diarrhoea mortality coincides with the decline of the tempera- 

 ture recorded by the 4 ft. earth thermometer, which temperature 

 declines very much more slowly than the atmospheric tempera- 

 ture, or than that recorded by the 1 ft. earth thermometer ; so 

 that the epidemic mortality may continue, although declining, 

 long after the last-mentioned temperatures have fallen greatly." 

 Possibly, as Mr. Baldwin Latham has suggested, the temperature 

 of the drinking water may be concerned in the production of 

 summer diarrhoea, but this temperature is largely dependent 

 upon that of the earth. 



The water of a moderately deep well, say, 50 ft. deep, is 

 approximately constant at about the mean yearly temperature of 

 the locality, but the water from superficial sources, such as 

 rivers and open reservoirs, varies greatly in temperature with the 



