52 GENERAL DIFFERENTIATION OF THE PL A NT- BODY 



one at all but is the prophyll of the first flower, and is made up of two 

 concrescent leaves in the axil of each of which stands a flower composed 

 of a single stamen. 



We are here forced to consider the formation of the flower as the 

 result of an arrest of the whole perianth, of five stamens, and of the 

 gynaeceum of the typical flower of Cyperaceae, accompanied by a con- 

 crescence of the two prophylls. Morphology which seeks to fathom 

 homologies constructs for itself an arbitrary starting-point, which may 

 either coincide with some living form, or may be an ideal type, and all 

 the relatives of one series are represented as deviations from this ' type.' 

 The deviations commonly result from either an arrest, a concrescence, 

 or a transformation, and these changes often stand in the clearest relation- 

 ship to the environment, or they are conditioned by internal relationships 

 of the organs to one another. Three methods are available to organo- 

 graphy for the recognition of the changes which have taken place in 

 the formation of organs comparison with allied forms, history of 

 development, and experiment. I have already dwelt upon the importance 

 of Experimental Organography, and have cited some confirmative illustra- 

 tions when speaking of the doctrine of metamorphosis in an earlier 

 chapter. It is one of the youngest branches of the study of organs, and 

 for it one may presage an important future, and therefore in a subsequent 

 chapter I will record the results which have up to now been obtained. 

 Of course experimental organography shades into physiology, but, as 

 I have already briefly pointed out, the separation of morphology from 

 physiology is a purely formal matter, and I include here within the 

 province of organography all those lines of investigation which touch 

 upon the formation of the organs of plants, no matter what methods 

 they employ. 



The notions of concrescence and of arrest have been applied at 

 different times in different senses, and it will not therefore be superfluous 

 if I examine them in some detail. Individual illustrations will be given 

 in the course of the second part of this book. 



CONCRESCENCE. 



The expression ' concrescence ' is used partly in a literal, partly in 

 a comparative sense, that is to say, it has been understood to convey 

 not only the fact that organs, originally separate from one another, unite 

 by their free parts, but also that many organs, which in certain plants 

 are found free and independent, are in others united with one another, 

 although this union is not brought about in the course of their development. 



One of the best-known examples is afforded by the corolla of the 

 Gamopetalae, which is usually described as composed of concrescent 



