l62 



EXTERNAL CONFORMATION OF PLANTS. 



The separate stamens appear as roundish protuberances on the floral axis, and each of 

 these immediately forms two or more roundish protuberances on its surface, after which 

 the same process is again repeated. When fully developed, the stamens (Fig. 131) appear 

 divided dichotomously or trichotomously upon long stalks, the branches being developed 

 somewhat irregularly. 



On an originally nionopodial branching depends, on the other hand, the form of the 

 pinnate, lobed, di^ided, cleft, and toothed foliage-leaves of Monocotyledons and Dicoty- 

 ledons '. The leaf appears on the vegetative cone as a roundish protuberance which 

 quickly broadens into a shell-like form (Fig. 132, ^, b), and grows vigorously at its apex. 

 Beneath the apex protuberances arise at the right and left angles in acropetal order ; 

 these also grow in the same manner at their apex (/), and produce again lateral pro- 



FiG. 1^2.— Development of the pinnate leaves of 

 Uinbelliferfe ; ^, B of Pastinaca sativa ; C of Lei'i- 

 st{cit>7! offia'nale: A the apical region of the primary- 

 stein ; its vegetative cone is seen at s, its youngest 

 leaf at b; b' youngest leaf but one with the pinnation 

 commencing ; C, bs the apex of the \&ia.i\/,fi,f'' the 

 leaf-branchesof the first order ; <i) of the second order. 



Fig. 133. — Leaves of Amorfihophallus buihosiis ; A with a simple, B with 

 a threefold branching of the lamina. 



tuberances of the second order (cjf)) ; and according to the extent to which the surface 

 of the leaf is developed, these protuberances become lobes of a simple leaf or distinctly 

 separated leaflets. 



When two rows of lateral branches arise successively in the middle of the leaf, 

 they generally remain weaker than it, and their lateral branches are also less numerous 

 and weaker; the development of such an originally monopodial branching-system of 

 leaves is therefore racemose. But the development may also be cymose, and may even 

 lead to the formation of sympodia, especially when only one branch arises right and left 

 on the leaf. This is the case, for instance, in the leaves of Helleborus, Rubus, and of 

 several Aroideae, as Sauromatum and Amorphophallus. Fig. 133 shows at ^ a weakly 

 leaf of the last-named plant with only one branch on each side ; but when the leaves 

 attain a more vigorous development, as shown at B, each lateral lobe, 2 2, forms on its 



^ This was first shown in detail by Nageli (Pflanzenphys Untersuch. von Niigeli und Cramer, 

 Heft 11.) in the leaves oi Aralia spifiosa. . . 



