Dr Davy's Agricultvral Discourse. 289 



out, its importance ; one word may suffice to convey an idea 

 of it, and even an adequate idea, viz., that manures are the 

 food of plants. And this definition suggests the analogy 

 that exists between plants and animals, and which I shall 

 dwell on for a moment, and revert to, because I believe it 

 to be instructive, or fitted to bring clearly to the mind some 

 general views, which may be an aid in discussing the sub- 

 ject, considered scientifically, that is, as regards principles, 

 or general rules deduced from facts or experience, and them- 

 selves applicable to practice. 



Plants and animals have in common the distinctive pro- 

 perty of reproduction, a power exercised by means either of 

 a bud, slip, seed, or ovum ; the seed of one being analogous 

 to the ovum of the other ; whilst the bud or slip-manner of 

 generation are common to both, and constitute one of their 

 most remarkable links. Having a common mode of origin, 

 so have they of growth ; as the animal grows, not like the 

 mineral from accretion from without, but by deposition from 

 within, so likewise does the plant. Both plants and animals 

 are nourished, and owe their growth to foreign matter intro- 

 duced from without ; and both cease to grow — both waste and 

 ultimately perish, if the foreign matter constituting their food 

 be withdrawn. To both, warmth, light, air, and moisture,>are, 

 in certain degrees, essential to their well-being ; and to both, 

 in other degrees, these are injurious. Wliilst there are thus 

 certain resemblances between plants and animals, there are 

 also marked and characteristic differences. The two most re- 

 markable are intimately connected with the subject under con- 

 sideration, — the kind of food required by each, and the kind of 

 organs belonging to each for its reception. A mouth and sto- 

 mach appear to be essential to the animal, in which the food 

 taken is prepared, more or less, for distribution and nourish- 

 ment. In the plant the preparation appears to be external — in 

 the soil, from whence the nutritive fluid is absorbed by the 

 delicate rooM, and by them conveyed for distribution where 

 required. Asto food, animals are dependent for their support 

 on one another, or on vegetables. Plants, on the contrary, 

 are not so dependent ; they derive their support from the soil 

 and from the atmosphere ; and whilst animals, in the act of 



