DEVELOPMENT OF THE MEMBERS OF A BRANCH-SYSTEM. 
On an originally monopodial branching depends, on the other hand, the form of 
the pinnate, lobed, divided, and toothed foliage-leaves of Angiosperms^ The leaf 
appears on the cone of growth as a roundish protuberance v^hich quickly broadens into 
a shell-like form (Fig. 140, A, b), and grows vigorously at its apex. Beneath the apex 
protuberances arise at the right and left in acropetal order; these also grow in 
the same manner at their apex (/), and produce again lateral protuberances of the 
second order (^) ; which, according to the extent to which the surface of the leaf is 
developed, become lobes of a simple leaf or distinctly separated leaflets. 
When two rows of lateral branches arise successively on the median axis 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 branch-system of leaves 
Fig. 140.— Development of the pinnate leaves of 
Umbellifera; ; A, B oi Pastinaca sativa; C of Levi- 
sttcum officinale; A apical region of the primary ¥IG. ii,z,~'LQSi'ics A moi'phophallu /'«//w/^j; ^ with a simple, 5 with 
stem ; its cone of growth is seen at s, its youngest a threefold branching of the lamina, 
leaf at b ; b' youngest leaf but one with the pinnation 
commencing; C, bs apex of the leaf ; y, y', leaf- 
branches of the first order ; (/) of the second order. 
is therefore racemose. But the development may also be cymose, and m^ay even lead to 
the formation of sympodia, especially when only one branch arises right and left on the 
primary leaf. This is the case, for instance, in the leaves of Helleborus, Rubus, and of 
several Aroideae, as Sauromatum and Amorphophallus. Fig. 141, ^ represents 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 
outer side again a lobe of the third order, 3 3, which again produces a similar one of the 
fourth order, 4 4, and so on. According to the general definitions given above, the first 
branch of the leaf, i, forms with 22a dichasium ; but each branch of the dichasium 
^ This was first shown in detail by Nägeli (Pflanzenphys. Untersuch, von Nägeli und Cramer, 
Heft II) in the leaves of Aralia spino&a. — See Eichler, Zur Entwickelungsgeschichte des Blattes 
(Dissertation, Marburg, 1861). 
