8 PREFACE. 



functions of animal life are suppressed, the vegetative life of 

 the organism gradually predominates, until life becomes wholly 

 vegetative. 



Life in plants is therefore limited to the two functions of 

 nutrition and reproduction ; and nutrition and reproduction in 

 animals are necessarily illustrated by the flowers and forest 

 trees with which the earth is beautified and adorned. Such 

 appears to me to be the way in which organic nature ought 

 to be regarded, such the relative positions of the vegetable 

 and animal creation. 



Few, we believe, recognize as they ought to do, the benefits 

 which have already resulted to animal physiology and the 

 science of medicine, from the study of a few humble plants. 

 The great cell-doctrine of physiology, which is now admitted 

 to be the basis of all sound scientific investigations into the 

 phenomena of organized beings, originated in the study of 

 vegetable matter. M. Mirbel, in a most admirable memoir on 

 the development of Marchantia polymorpha, a little aootyle- 

 donous plant belonging to the family of the Hepatiose, was 

 the first to show the cellular origin of every other form of 

 vegetable tissue. He proved that the fibre cells of plants are 

 only attenuated utricles, and that the different varieties of, 

 vasiform tissue aad ducts, by which the interior of the plant 

 is aerated, originate in a row of utricles ; these gradually elon- 

 gate, and the vai'ious secondary deposits characteristic of the 

 different forms of spiral vessels, appear on their internal sur- 

 face ; the septa or partition walls between the several cellules 

 are then absorbed, and the transformation of the utricles into 

 vessels is completed. These observations were confirmed by 

 the researches of Schleiden and. other distinguished botanists, 



