GEOGRAPHY OF PLANTS. 47 



species of plant has in some degree its own charter, one enjoying more ex- 

 tensive privileges than another. Nor, until we have ascertained the facts 

 regarding species bj particular observations, can we with certainty foretell 

 what will be the effect of change of climate upon them. What would be 

 more natural to suppose than that all the plants spontaneous at the Cape 

 of Good Hope, supposing they occurred at a tolerably uniform elevation 

 above the sea, would be influenced by change of climate in a like degree ? 

 Their native climate is a very remarkable one — remarkable for the intensity 

 and amount of solar light throughout the year ; for rapid changes of tempera- 

 ture, and for the very unequal distribution of moisture at different seasons. 

 We should expect among them a common feeling — so to say — on their re- 

 moval to this country ; and such, to a certain extent, is the case. But the 

 exceptions are very numerous ; for while some — such as the Heaths and 

 Pelargoniums — flourish and actually improve in the artificial climates of our 

 green-houses, others — as many of the bulbs — are with difficulty induced to 

 blossom, and rapidly degenerate. 



As might be expected, most Cape plants require the protection of glass 

 in winter ; but to this there are many remarkable exceptions. The Aga- 

 panthus flowers freely in the south of Ireland, in the open ground, from 

 year to year ; and the Tritomanthe (hot-poker plant) is even still more 

 hardy; for we have seen it raising its spike of scarlet flowers uninjured from 

 among the snow. Yet this plant is a native, not of high mountains or 

 table-lands, but of the low plains at the Cape, where the thermometer may 

 stand on a summer day in the ground, close to its roots, at a height of 130° 

 to 1 60°. When we find such wide discrepancies as these among plants of the 

 same region, we may well agree with our author in maintaining that the 

 question of the relation of plants to climate is a very complicated one ; and 

 that we can only rightly understand it by regarding plants as " living 

 machines," having a certain work to do, and struggling to perform it at all 

 hazards, fighting under difficulties against physical agencies. Beyond a 

 minimum of light, heat, and moisture, life ceases. With fair proportions of 

 these (according to the wants of each individual species) it is maintained 

 with vigour ; and there are a thousand intermediate stages of excess or de- 

 ficiency in which a struggle for existence is by the more hardy species 

 maintained. 



After discussing the effects of light, heat, and moisture in general, M. 

 de Candolle divides his subject into two principal sections, which he distin- 

 guishes by the names Geographic Botany and Botanical Geography. By 

 the first of these he understands the consideration of species, genera, and 



