Ififluence of Climate on Vegetation. 4 3 7 



Humidity is the next important point to be attended to 

 in cultivation. A certain degree of moisture is requisite to 

 render vegetable tissue elastic ; and, unless it possesses this 

 quality, it cannot expand into leaves and fruit. If kept too 

 dry, the spongioles of the roots wither, and lose their power 

 of absorbing food : the food of vegetables can, indeed, only 

 be absorbed when it is in a liquid state. Water is thus essen- 

 tial to the life of plants : but a certain degree of knowledge, 

 as to their nature and habits, is indispensable, to enable a cul- 

 tivator to administer it properly ; as, if too much be given, 

 and the plants kept too cold, they become dropsical, the 

 leaves swell and rot off, and the plant dies. This is particu- 

 larly the case with the Cacti, and other succulents; which 

 are natives of a country subject to long seasons of dry wea- 

 ther, and absorb moisture much more readily than they part 

 with it. When this is the case, if much water be given, the 

 vessels become loaded with moisture, circulation is checked, 

 and disease and death ultimately ensue. 



Air is the next essential point to be attended to. From the 

 atmospheric air, plants absorb the carbon which is considered 

 necessary for their support. If you deprive them of atmo- 

 spheric air, they languish, their leaves lose their colour, their 

 flowers their scent, and their fruit its flavour ; till by degrees 

 they pine away, and die at last absolutely for want of food. 



Light is the power which enables plants to decompose 

 atmospheric air, and to extract from it the carbon which is 

 necessary for their existence ; but, if exposed to more light 

 than is necessary for this purpose, they are fed too fast, and 

 die from over-excitement. All the secretions which give 

 taste and smell depend entirely upon light and air ; and it is 

 a remarkable fact, that all the most useful and finest flavoured 

 fruits are brought from countries where they have abundance 

 of brilliant light. Vines, Persian melons, dates, peaches, 

 pomegranates, and many other of the most valuable produc- 

 tions of the vegetable world, lose their finest qualities if not 

 grown in a strong light ; while fruits which grow naturally 

 in the shade, such as wild strawberries, apples, pears, &c., are 

 generally acid, and, when analysed, are found to possess very 

 little sugar. Important as light is to vegetation, it requires to 

 be regulated by a strict attention to the native habits of the 

 plant : too much and too little being alike injurious ; and, if 

 carried to excess, proving equally fatal in their effects. 



Temperature, humidity, air, and light being thus proved to 

 be all essential to the very existence of plants, it next becomes 

 necessary to enquire what combinations of them are requisite 



F F 3 



