DEVELOPMENT OF THE MEMBERS OF A BRANCH-SYSTEM. l8l 
the axis of growth of each shoot and through that of its immediate mother-shoot; 
then, in the hehcoid cyme each following median plane always stands right or 
left of the preceding one, following the course of the leaf-spiral ; in the scorpioid 
cyme, on the other hand, the consecutive median planes stand alternately right and 
left. 
(a) In Thallophytes and the Thalloid Hepaticge, dichotomy is very common, but 
monopodial branchings also occur developed in the most various ways. The dichotomous 
branching is unusually clear and generally bifurcate among Algae, especially in Dictyoteae 
and species of Fucus (in particular F. serratus). In some there occurs a tendency towards 
a sympodial development of the bifurcations, but usually only at a late period; so 
that the dichotomous branching can be clearly recognised at the ends of the branches 
even with the naked eye. The same is the case, among Hepaticae, in Anthoceroteae, 
Riccieae, Marchantieae, and in Metzgeria (Fig. 137), where a flat expansion of the thallus 
or thalloid stem arises between 
the young bifurcations, first of 
all as a protuberance (/' /"), 
which however cannot be con- 
sidered as a coutinuation of 
the shoot, since it has no apical 
cell or mid-rib ; subsequently 
this protuberance disappears, 
as m/"'\ 
Distinctly monopodial (lar. 
teral) ramifications are parti- 
cularly clear in filamentous 
Algae, when the apical cell re- 
mains unbrancbed, and lateral 
branches grow only out of the 
individual cells (segments of 
the filament); as in Cladophora, 
Lejolisia, Sec. It occurs how- 
ever sometimes that lateral 
branches proceed out of the 
apical cell itself, as is espe- 
cially shown in Stypocaulon (Fig. 108, p. 139). In other cases the branching of the 
apical cell is dichotomous, as in ColeochcBte soluPa (see Book II, Algae). 
(b) In the roots of Ferns, Equisetaceae, and Rhizocarpeae, as well as in those of 
Conifers, Monocotyledons^ and Dicotyledons, the branching is always, as far as is known, 
at first monopodial, and even at a later period the primary root generally remains stronger 
than its lateral roots ; these root-systems are therefore developed in a racemose manner 
(Fig. 133, p. 165); this is seen very beautifully in the root-systems which proceed from 
the primary roots of Dicotyledons when they are allowed to germinate and grow in water. 
Dichotomy of roots occurs only in Lycopodiaceae, and probably in Cycadeae, where they 
appear at a later period as systems of bifurcations. According to the most recent 
researches of Nageli and Leitgeb, it is still altogether doubtful whether the branching 
depends, even in Lycopodiaceae, on true dichotomy ^ ; but the root-branches of Lycopo- 
^ For the above-mentioned reasons I share Kny's view that the branching is in this case 
dichotomous. (See Hofmeister, Allgemeine Morphologie, p. 433.) 
Compare Nageli's Beiträge zur wissen. Botanik, Heft IV, 1867. I would lay less stress on the 
relation of dichotomies to the apical cell, because the latter has scarcely the same decided signifi- 
cation in Lycopodiacese as in Ferns, Equisetaceae, and other Cryptogams; and the apical growth 
apparently approaches nearer to that of Phanerogams. 
Fig. 137. — Flat thallus of Hfitz^eria furcata branching dichotoniously 
(X about 15); }!i >n mid-rib con^sisting of' several layers, branching dichoto- 
mously at s s apical points of the branches ; y / the wing-like expansions 
of the thallus, consisting of one layer of cells -; y"'y" the wings between the 
mid-ribs of younger branches. (The left-hand figure is seen from below, the 
right-hand one from above.) 
