ON THE INFLUENCE OF CLIMATE ON PLANTS. 
157 
subject, is the necessity of shading the house with thin canvass during the heat of 
the day in the summer months. This canvass should be so placed that it may be 
rolled on or off the house at pleasure, and it should always be removed when the 
sun is not shining too fiercely, as it is only a great intensity of solar light which 
injures these plants, and they should never be secluded from light when the sun is 
not shining. It is the necessity and propriety of shading which we have all along 
had in view in speaking of these plants, and to this we again earnestly urge the 
attention of our readers. It is true that some few of the species of this genus are 
found in situations where they are exposed to great drought, caused by the 
intensity of the sun's rays during a brief portion of the year ; but it should not be 
forgotten that many of these grow naturally in a loamy soil^ which every one will 
admit is more retentive of moisture than that in which we usually place them. 
And, again, — others that inhabit exposed localities, grow in mountainous districts, 
or even in the clefts of rocks, in which case their roots are supplied with moisture 
from the portions of rock which surround them, as these constantly retain a greater 
or less degree of it. Besides, who will attempt to argue that a plant, the roots of 
which are confined in a pot, and that pot, as well as the surface of the small portion 
of soil it contains, exposed to the full action or influence of the sun — is not more 
liable to injury from exhausting evaporation, than one in a situation where only 
the surface of the soil in which it is growing is exposed, and where it must likewise 
always receive some moisture by absorption from the sub-soil ? No one, we feel 
assured, can for a moment entertain such an opinion, much less endeavour to 
support it. Therefore, admitting that certain species of this genus are found in 
those localities where they are occasionally subjected to a great degree of solar light 
and heat, and consequently of drought, we maintain that even in such situations 
they possess great advantages over those which are kept in our greenhouses, 
enjoying counteracting influences which the latter do not, and are thus enabled to 
endure the full blaze of a summer's sun. But it is notorious that the majority of 
them are met with in more or less shaded positions ; and this proves that we are 
not deviating from nature's treatment in proposing an artificial shading for them 
in those purely artificial situations and unnatural circumstances under which they 
are here cultivated. Indeed, we confess that we should not scruple to depart from 
the precepts of nature, where, owing to the adventitious and foreign influences to 
which they are necessarily subjected, a system of treatment could be found more 
congenial to the habits of natural productions when under artificial cultivation ; but 
where that system has not and cannot be ascertained, (which is the case with most, 
we do not say all plants,) we deem it advisable and expedient to adhere as strictly 
as possible to the course prescribed by nature ; and when by experiment and 
investigation other systems are found to be more suitable, we shall willingly and 
gladly adopt them. We therefore again repeat, that every person who is desirous of 
making any advancement in the cultivation of heaths, should have them collected 
into one house, placed at a slight distance from the glass, and shaded from the 
