296 



TEMPERATURE TO WHICH PLANTS 



day not exceeding 86°. These facts throw quite a new light 

 upon the nature of Australian vegetation. 



It may be supposed that so low a temperature must have been 

 accompanied by extreme dryness, and such appears to have been 

 usually the case. Nevertheless, it cannot have been always so, 

 for although we have no hygrometrical observations for June 

 and July, and only four for May, yet there is other evidence to 

 show that the dryness cannot always have been remarkable. 

 In May the hygrometer indicated •764, -TOS, •934, or nearly 

 saturation, and •596; yet the sun-rise temperature was on those 

 occasions 25°, 28°, 30°, and 34°. On the 22nd of May the grass 

 was white with hoar frost, and then the thermometer was at 

 sun-rise 20° under canvas and 12° in the open air ; and on the 

 5th of July, when it rained all day and the tents were "frozen 

 into boards," the thermometer sank during the night from 38° 

 to 16°. 



It is probable that this power of resisting cold is connected with 

 the very high temperature to which Australian vegetation is 

 exposed at certain seasons, and this is horticulturally a most im- 

 portant consideration. We find that in latitude 32° S. in .January 

 (our July) the thermometer stood eight days sviccessively above 

 100°, and even reached 115° at noon; that it was even as 

 high as 112° at four p.m. ; that in the latter part of February 

 one degree nearer the line it was twice 105" and once 110° ; that 

 in March one degree further nortlnvard it frequently exceeded 

 100°, and there was not much fall in this excessive temperature 

 up to the end of April. This will be more evident from the 

 followinq: 



At this time the dryness must also be excessive, as will have 

 been seen by Sir Thomas Mitchell's observations.* 



Even such heats as these do not, however, destroy the power 



* The humidity of the atmosphere, as indicated by a wet bulb thermo- 

 meter, does not, however, give such a degree of dryness as might have been 

 anticipated ; but it is to be suspected that some errors may have crept into 

 this part of the Journal. 



