1244 '^ TEXTBOOK OF THEORETICAL BOTANY 



positions, appear to be normal and functional (see also p. 1 195). Too much 

 weight can easily be given to such phenomena as evidence in questions of 

 phylogeny. Their immediate causation is practically unknown and their 

 ultimate causation purely speculative. 



The morphology of carpels has been treated at some length because they 

 are, of all the organs of the plant, the ones most essentially characteristic of 

 the Angiosperms, and this remains true whatever theory of their origin we 

 may adopt. It is for this reason that so much importance has been given to 

 them in classification, where they have sometimes been overweighted w^hile 

 other parts, such as the stamens, have been accorded too little significance. 

 To separate families on the ovarial structure alone smacks of artificiality. 



It may be useful here to sum up the classical theory of the flower, as it 

 has been redefined by Eames, as being at least a good working hypothesis. 



The flower is a determinate shoot with phyllome appendages. Pedicels 

 and receptacles have typical stem anatomy and the appendages are leaf-like 

 in their anatomy and development. Sepals are three-trace organs and are 

 morphologically bracts and not sterilized sporophylls. Petals are one-trace 

 organs and, though showing some leaf characters, mostly appear to be 

 sterilized stamens. Stamens are one-trace organs, like petals, and are only 

 three-trace in a few primitive families. Carpels are predominantly three- 

 trace organs and are only abnormally one or many-trace. Both stamens 

 and carpels appear to be sporophylls. 



Fusion of organs may lead to the fusion of their vascular supplies, either 

 radially or tangentially. 



NECTARIES 



The nectar glands, on which depend the pollination of the great majority 

 of flowers, form a category of organs of doubtful homogeneity, since some 

 are obviously produced by the modification of other parts of the flower, 

 while others have the appearance of being special structures or specialized 

 outgrowths of existing structures. They are by no means always insignificant 

 in size but may rival or even exceed the dimensions of the gynoecium, 

 although they may be nothing more than emergences. Outgrowths in the 

 flower which have the character of trichomes or emergences are called 

 effigurations. Some structures of this kind may serve as nectaries (Fig. 

 1 199) but others appear to be functionless or to have only secondary func- 

 tions in connection with pollination. Like the nectaries, effigurations are of 

 mixed origin and may occur in any part of the flower. It is an unsatisfactory 

 category, something of a rag-bag, to which all sorts of unexplained structures 

 may be relegated. 



Despite the varied origin of nectaries, those of certain families, for 

 instance the Cruciferae, are so characteristic that they have been made use 

 of in classification, especially within the family. Bayer proposed to sub- 

 divide the Cruciferae on the basis of the nectary forms, which are illus- 

 trated in Fig. 1200. He concluded that the whole surface of the receptacle 



