98 



EXTERNAL CONFORMATION OF PLANTS. 



the causes which most commonly co-operate to produce these results may be mentioned ; 

 they may be termed Displacement^ Adhesion, and Abortion. Very commonly the two 

 first act simultaneously, and in many flowers combine with abortion to produce complex 

 organs difficult to explain. It belongs to the most beautiful problems of morphology 

 to refer such apparent exceptions to more general laws of development ; and the 

 determination of natural affinity, the fixing of the typical properties of whole classes, 

 orders, and families, depends upon it. Since, however, these complicated phenomena 

 belong almost exclusively to Angiosperms, and in them occur to much the largest extent 

 in the flowers and inflorescences, the best place for a more detailed description will 

 be when the characteristics of this class are under consideration. Some explanation 

 may, however, be given here, by means of a few examples, of the use of the terms 

 Displacement, Adhesion, and Abortion. 



The diagrammatic Fig. 149 shows a branch-system developed sympodially and pro- 

 ceeding from an axillary shoot ; i, i being the first shoot with its two leaves i^ and i^ ; in 

 the axil of the leaf i^ is developed the shoot 2, 2, with its two leaves 2% 2^ ; in the axil of 

 its leaf (2^) again arises the lateral shoot 3, 3, with its leaves 3% 3^, and so on. The parts 

 of the stem of the shoots 1,2,3,4, which proceed from one another, form a straight pseud- 

 axis (sympodium) with the peculiarity that the mother-leaf in whose axis the lateral shoot 



Fig. 149. — Diagram of the adhesion of leaves 

 with the axial parts of their axillary shoots (after 

 Nageli and Schwendener ; Das Mikroskop). 



FIG. \^o.— Her minium Monorchis {after T. Irmisch: Biologie und 

 Morphologic der Orchideen. Leipzig 1853). 



developes adheres to it, and is carried up by it for some distance. If we call the 

 globular ends i, 2, 3, 4 of the figure flowers, the whole is well adapted to represent 

 diagrammatically the inflorescence of some Solanaceae. If the leaves i*, 2% 3% 4* are 

 supposed to be removed, the diagram might stand for the primary branch of the inflo- 

 rescence of Sedum. If, on the other hand, a lateral shoot is supposed to be formed in 

 each case in the axil of the leaves 1% 2% 3"'^, 4^ in the same manner as on the other 



