1 84 
MORPHOLOGY OF MEMBERS. 
developes further only on one side, the new branches always arising either only on the left 
or only on the right side, 3 from 2, and 4 from 3 ; every lateral branch thus produces a 
sympodial system, and in fact a helicoid cyme. 
If now the basal pieces 2, 3, 4, combined in a sympodial manner on both lateral shoots, 
are imagined to be much shortened, so that the bases of the lobes 2, 3, 4 come close to 
the base of the lamina i, then all the lobes of the leaf will appear to spring from one 
point, and the leaf is called digitate. It would appear, however, that such leaves may also 
arise by the formation from the broad end of the young leaf itself, first of a middle lobe, 
and then of new lateral lobes right and left from above downwards, as in Lupinus, 
according to Payer's drawings (Organogenic de la fleur, pi. 104). If the lobes remain 
completely united or have the appearance of a continuous lamella, we have a peltate 
leaf ^. It is impossible to go more into the detail of these processes without numerous 
illustrations which cannot be given here. Fig. 142 will explain, in conclusion, the 
origin of the quadripartite lamina of the leaf of Marsilea Dnimmondi, according to 
a protuberance {stb) arises on both sides ; and while the latter (destitute of an apical 
cell) becomes still more arched (C, stb), the apical growth of the leaf ceases (C, bs), its apical 
cell disappears, and soon two equally strong outgrowths arise near the apical point, which, 
like the earlier lateral ones, increase vigorously and grow out into broad lobes of the leaf. 
Thus arises a quadripartite lamina at the end of the petiole, the lateral lobes of which 
have resulted from lateral branching, but the middle ones by dichotomy. The four 
lobes remain, as they grow, narrow at their base, becoming much broader at the free 
margin ; and, since the part of the leaf from which they originated remains short and 
narrow, they appear, in the mature leaf, to spring from a single point, the end of the 
petiole. 
(d) Branch-system of Leaf-bearing Shoots. The branching of the stem of Lyco- 
podiaceae is dichotomous. In Psilotum triquetrum all the branches develope uniformly; 
and this is the most regularly developed dichotomy found among vascular plants. 
In Lycopodiese the development is much more irregular, but the bifurcation is 
always evident throughout ; in Selaginelleae, on the other hand, it is generally to be 
Fig. 142.— Development of the leaf of Marsilea Drttvimondi (after Hanstein). A, C, D 
seen from the inner surface; ß longitudinal section vertical to ^ ; bs apex of the leaf; 
g—z the segments of the apical cell; stb lateral lobes of the lamina in their earliest state. 
Hanstein (Jahrb. für. 
wissen. Bot. vol. IV). 
The leaf has its origin 
in a cell of the cone 
of growth of the stem, 
which, becoming the 
apical cell of the leaf, 
produces two rows of 
segments from which 
the right and left halves 
are formed. Thus a 
broad cone first arises, 
growing at its apex, and 
bent towards the stem 
{A, B) ; when this, 
which is the future 
petiole, has attained a 
certain height, it in- 
creases in breadth right 
and left. Beneath the 
still growing apex, D, bs, 
^ Compare further Trecul, Formation des feuilles, in Ann. des Sei. Nat. vol. xx. 1853; and 
Payer, /. c. p. 403 ; also Entwickelung der Blattgestalten, Jena 1846. 
