PREFACE. 11 



Dr. Draper, in reference to the exciting causes of the motion 

 of the nutritive fluids in the organism of plants and animals, 

 notwithstanding the attempts which have heen made to con- 

 trovert them. , Let it be considered that there is the same suc- 

 cessive degrees of attenuation in the conduits of both the sap 

 and .blood, resulting from lateral ramifications ; the same beau- 

 tiful anastomoses amongst the capillaries in which these con- 

 duits finally terminate. By these means the nutritive fluids 

 are difi'used in all directions, and brought into immediate com- 

 munication with the cellular tissue of the organs. Let the 

 structure of any exogenous leaf be examined even superficially, 

 without the microscope. The successive attenuations of the 

 fibrous system by lateral ramifications into a network of capil- 

 laries, which develop horizontally in a series of closely approx- 

 imated planes, through the parenchyma of the leaf, show that 

 the same laws predominate in the distribution and elaboration 

 of fluids in vegetable as in animal matter. At least it is not 

 unphilosophical to infer some analogy, if not absolute identity 

 of function, where there is so manifest a similarity in organic 

 structure. 



I cannot conclude my Preface without acknowledging my 

 obligations to my numerous friends and patrons through whose 

 assistance I have been enabled to produce this volume. 



In the preparation of Part I. an excellent Chevalier micro- 

 scope was employed. This instrument was kindly lent me by 

 Dr. Francis Lewis. It gives me pleasure also to mention the 

 services of Dr. Samuel Jackson, Dr. Samuel Lewis, Dr. Francis 

 West, Dr. S. Tucker, the Hon. W. D. Kelly, and Professor 

 Saunders of the French Collegiate Institute, "West Philadelphia, 



