CHARACTERISTIC FORMS OF LEAVES AND SHOOTS. ' 219 



of abnormal formations, yet the causes which most commonly produce these results 

 may be mentioned ; these may be included under the heads displacement, adhesion, and 

 abortion. Very commonly the two first act in unison, 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 definition of the typical 

 characters 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. 



Fig. 157 represents diagrammatically a branch-system developed sympodially and 

 proceeding 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 i, 2, 3, 4, which proceed from one another, form a 

 straight pseud-axis or sympodium with the peculiarity that the mother-leaf in whose axis 

 the lateral shoot 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 1% 2% 3% 

 4^ are supposed to be removed, the diagram might stand for the primary branch of the 

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

 in each case in the axil of the leaves i*, 2% 3% 4* in the same manner as on the other 

 side with displacement of the mother-leaf, this would repeat diagrammatically in a simple 

 manner the branching and phyllotaxis of Datura ^. 



Still more complicated are the phenomena in Fig. 158, where /represents the lower 

 part of a flowering plant of Herminium Monorchis. t t \s the surface of the ground, and 

 what lies below this is therefore underground : 5 is a swollen spherical root, above 

 which rises the leaf-bearing shoot, which produces in its lower part slender lateral roots, 

 iv, nu, eiv, as well as a sheath-like scale ^ b, and two foliage-leaves c, d, and continues 

 higher as a slender scape j4, bearing a raceme of flowers at its summit. Turning our 

 attention exclusively to the structure H; we find it to be a shoot which contains the bud 

 for the next year ; for the whole plant A, Bm I dies off" after flowering, a similar plant 

 being produced the next year from the bud contained in H. H is therefore an axillary 

 shoot of the scale b, an earlier condition being represented in Fig. ///, where M repre- 

 sents the base of the leaf I? cut through its median plane ; ^ is a fibro-vascular bundle 

 running from the primary axis to the bud m; ^/ is the first leaf of this bud u which 

 is placed with its back to the mother-axis and forms a diminutive sheath enclosing 

 the succeeding leaves of the bud « ; B^ is the young tuberous root with its root-sheath v. 

 In order to understand the displacement which has already taken place, the whole lower 

 part between M and 'v must be imagined shortened to such an extent that B"^ would be 

 somewhere near the letter g ; and the bud u must be supposed at the same time moved 

 backwards towards 0. By this means the normal position of the parts of H under con- 

 sideration is restored, and it is intelligible that the channel /, inclosed by the base of the 

 leaf bl, is a consequence of the oblique direction outwards of the growth of the tissue 

 lying between and u, that the root-sheath 'v must be regarded as a part of the surface 

 of the primary axis above M, and that in consequence B"^ has been formed in the 

 tissue of the mother-axis beneath the bud u, and laterally on the fibro-vascular bundle g. 

 In the normal position of the bud and root, the axis of growth of the latter would form 

 almost a right angle with that of the bud, whereas by the displacement one forms a 



' [See Payer, Elements de Botanique, p. 117.] 



* A first scale in the axil of which the bud k stands is no longer to be seen. 



