204 Dr. Mac Culloch on the 



merely, nor is it a difference in the mean or the summer temperature; 

 since it would be abundantly easy to produce geographical proofs 

 of this, could I here enter on a subject of such detail. Nor is 

 there any solution to be given but that of the differences of light: 

 an explanation indeed which ought not to be questioned, since the 

 effects of this in ordinary horticulture, as to fruits, are acknow- 

 ledged, whether for benefit or injury, as it shall exceed or fall off. 

 That a register of light ought to form an essential ground of 

 judgment on agricultural questions, relating to territorial or 

 geographical position, is a conclusion naturally following from 

 this view. 



The deficiency of light in Guernsey is not such as to interfere 

 with its flowers, as the season of flowers is its purest summer : but 

 the want is decidedly marked in autumn, and especially in respect 

 to the difficulty of ripening grapes out of doors, in which it 

 is inferior to the English central counties, which produce grapes 

 in this manner. It is usual to attribute this to defect of heat ; 

 but the heat of Guernsey, by the register is, at that late period, 

 equal to the heat of the English counties in question, though the 

 cloudy atmosphere renders the light inferior. And if the effect 

 of greenhouses does, as is unquestionable, depend, in a great 

 measure, on the heat which they concentrate, it is not to be for- 

 gotten that one of these effects is to bring forward the fruit, so 

 that its period of maturity shall approach nearer to that season in 

 which light is most abundant. This conclusion is indeed amply 

 confirmed by the effect of cloudy summers, even on the grapes of 

 the greenhouse. 



Thus much it was necessary to say respecting this climate, as 

 concerned with the peculiar appearances of its horticulture, and I 

 must proceed to describe the few facts, as to individual plants, 

 which may be in any way interesting. One of the objects is here 

 to show, that certain plants of hot climates differ materially in 

 hardiness from others, as a temptation to try more widely the ex- 

 tent of this law. Another is, to demonstrate the injury which 

 many plants, perhaps all, receive from confinement, as an induce- 

 ment to further trials on plants which have hitherto disappointed 



