INTRODUCTION. XXV 



trary definition of teratology or to trace the limits 

 between variation and malformation, it may suffice to say 

 that vegetable teratology comprises the history of the 

 irregularities of growth and development in plants, and 

 of the causes producing them. These irregularities 

 differ from variations mainly in their wider deviation 

 from the customary structure, in their more frequent 

 and more obvious dependence on external causes rather 

 than on inherent tendency, in their more sudden ap- 

 pearance, and lastly in their smaller liabihty to be 

 transmitted by inheritance. 



What may be termed normal morphology includes 

 the study of the form, arrangement, size and other 

 characteristic attributes of the several parts of plants, 

 their internal structure, and the precise relation one 

 form bears to another. In order the more thoroughly 

 to investigate these matters it is necessary to consider 

 the mode of growth, and specially the plan of evolution 

 or development of each organ. This is the more 

 needful owing to the common origin of things ulti- 

 mately very different one from the other, and to 

 the presence of organs which, in the adult state, 

 are identical or nearly so in aspect, but which never- 

 theless are very unlike in the early stages of their 

 existence.^ Following Goethe, these changes in the 

 course of development are sometimes called metamor- 

 phoses. In this way Agardh' admits three kinds of 

 metamorphosis, which he characterises as : 1st. Suc- 

 cessive metamorphoses, or those changes in the course 

 of evolution which each individual organ imdergoes in 



' Wolff was the first to call attention to the great importance of the 

 htudy of development. He was followed by Turpin, Mirbel, Schleiden, 

 Payer, and otliers, and its value is now fully recognised by botunista. 



Agardh, " Theoria Syst. Plant.," p. xxiii. 



