186* On the Connection between the Leaves and Fruit. 



part of essential oils. The remarkable low temperature re- 

 quired to freeze these viscid compounds, directed my atten- 

 tion to the composition of the juices, and to the parenchy- 

 matous parts of the Willow, the Holly, the Misletoe, and the 

 Alder ; and also to the physical composition of many Ever- 

 greens. Some of those, as the Box, extend over a wide range 

 of climates, and others which have been transported hither 

 from mild regions, bear the frosts of this country with im- 

 punity. The causes of this capability in plants of enduring 

 such vicissitudes, are worthy of research, because the results 

 may, as before intimated, teach us how to ascertain those 

 vivacious properties, both in exotics, and in the new varieties 

 of our own culture.* 



The advancement of vegetable physiology has been too 

 long retarded by a continued effort to force upon it analogies 

 with the structure and offices of animal organs. The ways 

 of nature are, however, not limited by confined rules like 

 those of man; her diversities are endless; and she is not 

 obliged to work by any methods of system, of analogy, or of 

 classification. Such methods are indeed great (if not indis- 

 pensible helps) to human knowledge ; but when we attempt 

 to impose them upon the works of creation, we often darken 

 and dull the evidences of our senses, and confuse the opera- 

 tions of reason. 



The leaves of plants have been compared to the lungs of 



* The generality of winter buds are admirably adapted for resisting frost, by 

 the compacted and dry state of their spongy substance ; the buds of the Horse- 

 chestnut are coated with a viscid varnish, which is impenetrable to rain or dew. 

 Most of the other species of winter buds are equally protected against evapora- 

 tion from within, and moisture from without, by dense shelly coverings. 



