4 1 4 Analogy between Plants and Animals. 



leaves. An animal can no more live without its lungs than 

 without its stomach. The stomach, as we have seen, is neces- 

 sary for the turning of food into chyle, and the lungs for turning 

 that chyle into blood. Now, a plant can no more live and grow 

 without leaves, than an animal can without lungs. The use of 

 the lungs is to expose the chyle to the action of the air, which 

 they decompose, so that its oxygen may unite with the chyle, 

 and thus change it into blood. The leaves of plants, which 

 act to them as lungs, not only decompose air, but light, in the 

 process of elaborating the sap ; and, hence, plants can no more 

 live without light, than without air or food, as light is neces- 

 sary to turn their food into sap, or, in other words, to bring 

 it into the proper state for affording them nourishment. Hence, 

 in the culture of plants, the great importance of light. An 

 important difference, however, between the circulation of the 

 sap in vegetables and the blood in animals is, that the former 

 have no heart. 



Plants and animals agree in requiring a certain degree of 

 temperature to keep them alive ; and the warmth of this tem- 

 perature 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 main- 

 tained by art ; either by a suitable situation in the open air, or 

 by its culture under a structure which admits the light, and is 

 capable of having its atmosphere heated to any required degree. 

 The temperatui'e 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. 



Plants agi'ee with animals in requiring periodical times of 

 rest. In animals, these periods are, for the most part, at short 

 intervals of not more than a day ; but, in plants, they are com- 

 monly at long intervals, probably of a year. 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 

 dormant season in plants commences with the cold of winter, 

 and continues till the recurrence of spring. When plants are in 

 a dormant state, they commonly lose their leaves, and, conse- 

 quently, 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 are 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 



