ANALOGY BETWEEN PLANTS AND ANIMALS. 5 



affording them nourishment. Hence, in the culture of plants, the great im- 

 portance of solar light. An important difference, however, between the cir- 

 culation of the sap in vegetables and that of the blood in animals is, that the 

 former have no heart. 



10. Plants and animals agree in requiring a certain degree of temperature 

 to keep them alive ; and the warmth of this temperature differs greatly in 

 the different kinds both of plants and animals. Hence, the constitutional 

 temperature of any plant to be cultivated being known, that temperature 

 must be maintained by art ; either by a suitable situation in the open air, 

 or by its culture within a structure which admits the light, and is capable 

 of having its atmosphere heated to any required degree. The temperature 

 which any plant requires is ascertained by its geographical position in a wild 

 state, making allowance for the difference produced in the habits of the plant 

 by cultivation. 



11. Plants agree with animals in requiring periodical times of rest. In 

 animals, these periods are, for the most part, of short intervals of not more 

 than a day ; but, in plants they are commonly at long intervals, mostly of 

 several months. In warm climates, the dormant period of plants commences 

 with the dry season, and continues till the recurrence of the periodical rains, 

 which are peculiar to the tropical regions. In temperate countries, the dor- 

 mant season in plants commences with the cold of winter, and continues till 

 the recurrence of spring. When plants are in a dormant state, they com- 

 monly lose their leaves, and, consequently, at that season, they are unable to 

 make use of the nourishment applied to their roots ; and hence the injury 

 done to them when they arc stimulated with nourishment and warmth, so 

 as to occasion their growth during the period at which they ought to be at 

 rest. Hence, also, arises the injury which plants receive, and especially 

 bulbs, if the soil about them be kept moist by water when they are in a 

 dormant state. Plants having no feeling, in the common sense in which the 

 word is used, can neither experience pleasure nor pain ; but they resent 

 injuries, either negative or positive, by slow growth, or by becoming diseased. 

 By their being fixed to the spot where they grow, they necessarily depend for 

 their food, heat, air, and light, on the circumstances peculiar to that spot ; 

 and, hence, to increase their growth beyond what it would be if left to 

 nature, additional food must be brought to them, and the warmth, airiness, 

 and lightness of the situation increased. Hence, what is called vegetable 

 culture, which, with plants in general, consists in stirring the soil, adding 

 manure to it, regulating the supply of water by draining or irrigation, shel- 

 tering from the colder winds, and exposing to the direct influence of the sun's 

 rays. If we imagine any one of these points attended to, and not the others, 

 the plant will not thrive. Stirring the soil, and mixing it w r ith manure, will 

 be of little use, if that soil be liable to be continually saturated with mois- 

 ture, either from its retentive nature, from springs from below, or from 

 continued rains from above ; or if it be continually without, or with very 

 little, moisture, from its porous nature, the want of moisture in the subsoil, 

 and the want of rain and dews from the atmosphere. Improving the soil 

 without improving the climate (that is, without communicating a propor- 

 tionate degree of warmth and light), will increase the bulk of the plant, but 

 without proportionately bringing its different parts to maturity. For ex- 

 ample, we will suppose two plantations of trees planted at the same time, 

 on similar soil, and in the same climate ; that in the case of the one plantation 



