INTRODUCTION. 7 



forth and proffers to him as food, but agriculture must 

 furnish him with the means to satisfy his increased 

 necessities. But man only ploughs the field and strews the 

 seed; in faith he awaits a blessing from above. All 

 vegetation depends far more closely than is usually believed 

 upon the phenomena which, in sunshine and cold, drought 

 or rain, in the storm or the soft breath of the south- 

 western breeze, constitute that which we call weather and 

 climate. We shall, therefore, justly make the considera- 

 tion of Weather precede the investigation into the nutrition 

 of plants (v). 



While the fact of the plants preparing their nutriment is 

 the most important basis for the existence of the animal 

 world upon the earth, man is also entitled and enabled by 

 his industry to make an incomparably greater use of plants 

 and the matters contained in them. Thus is opened a new, 

 and, indeed, almost unbounded field. Need I enumerate all 

 the crafts which derive the material on which their labours 

 are exerted from the vegetable kingdom ? Every one who 

 looks around his chamber or his household, will be at once 

 aware of how many of the conveniencies and pleasures of 

 life he must be deprived if the vegetable world should cease 

 to pay its tribute. Need we open all the drawers and 

 boxes of the grocer or the druggist, to see what a store 

 of means vegetation contributes here also? A general 

 summary would give but a dry catalogue of names ; a 

 detailed account of all would occupy many volumes. We 

 will be content with a single example, and examine some- 

 what closely the Milky Juices of plants (vm) . 



The formation of milky juices is not confined to one, 

 notf to a small number of allied plants, but we find at least 

 three very large groups, which principally furnish this inte- 

 resting substance. The number of distinct species of plants 



