x Suggestions for Further Study 197 



than in English ones. Warming's Systematische Botanik 

 will serve the student as the best guide to Baillon's Histoire 

 des Plantes and Engler and Prantl's more full and recent 

 Pflanzetifamilien, while a more modest acquaintance can 

 be obtained from any of the ordinary manuals, large or 

 small. The article, "Vegetable Kingdom," of Chambers's 

 Encyclopedia and the Britannica may also be consulted ; 

 with their minor articles on the particular natural orders 

 and on special plants ; while the historical evolution of 

 this field of science is outlined in Chambers at BIOLOGY, 

 BOTANY, and BOTANIC GARDEN. 



Morphology of Organs (Comparative Anatomy). With" 

 our widening survey of plants increases our knowledge of 

 bionomics, our grasp of individual and general physiology, 

 but also our anatomical knowledge and skill. We thus 

 acquire a wide acquaintance with the forms of leaf, of stem, 

 and root, as well as with their life ; why should we not 

 generalise this knowledge also, and consider each of these 

 organs apart from its function ; so developing a highly 

 abstract science of " pure morphology " a crystallography, 

 as it were, of the organic world ? A leaf in the physiological 

 sense we saw to be the organ of transpiration and assimila- 

 tion ; but a stem may do the same, even an unearthed 

 potato. Shall we define it by its usual form, its bilateral 

 symmetry, its two surfaces? But to these characters there 

 are many exceptions ; and, moreover, stems may flatten 

 out into what are, in general aspect as well as function, 

 excellent leaves. Seeking a yet more general character, 

 we say, morphologically speaking, leaves are appendages of 

 an axis the stem, i.e. arise upon it, and never from each 

 other. Now arises a new set of physiological difficulties, 

 well seen in the prickly pear. Here the great flattened 

 joints, so like huge succulent leaves in appearance and 

 function, are branches, i.e. secondary axes ; the true leaves 



