DISTINCTION BETWEEN MEMBERS AND ORGANS. 
(c) General ideas, like those considered here and in the sequel, depend always on 
abstractions; they therefore necessarily want the practical clearness of the particular 
ideas from which they have been abstracted. How far the abstraction may be carried is 
more or less arbitrary; and the only correction for this lies in the scientific usefulness 
of the idea. Those ideas are the most useful which, from the greater precision of 
the definition, and from their greater clearness, include the greatest possible number 
of particular cases ; for in this manner is that complete general comprehension of the 
phenomena most easily obtained which must precede a closer examination of them. The 
definitions in the following paragraphs are given from this point of view. 
Sect. 21. Leaves and Leaf-bearing Axes\ — The members of the plant 
which are called Leaves (Phyllomes) in Characese, MuscineDS, Vascular Cryptogams, 
and Phanerogams, are related to 
the axis or stem from which they 
are derived in the manner de- 
scribed in the following para- 
graphs. 
(1) The Leaves ahvays origi- 
nate heloiv the groiuing apex of the 
stein as lateral outgrowths, either 
singly, or several at the same 
height, i.e. at an equal distance 
from the apex ; in the latter case 
they form a whorl, the single 
leaves of which may differ in age, 
as in Chara and Salvinia, and in 
the whorls of many flowers. 
(2) So long as the apex of 
the shoot continues growing in a 
straight line, and the portion of 
the shoot which produces leaves 
lengthens, the leaves arise in 
acropetal order ; i. e. the nearer 
the leaves are to the apex, the 
younger they are. In this case leaves are never produced further from the apex 
than those already in existence. It is only when, as not unfrequently happens 
with the flowers of Phanerogams, the growth in length of the shoot ceases or 
becomes weaker at the apex, while, at the same time, active growth continues in 
a transverse zone or place beneath the apex, that new leaves can arise between 
those already in existence ^. 
{3) The Leaves alivays originate from the Primary Meristem of the Groiving 
Fig. 116.— ■Longitudinal section through the apical region of a stem of 
Fontinalis a7itipyretica, an aquatic Moss (after Leitgeb) ; v the apical cell 
of the shoot, producing three rows of segments which are at first oblique 
and afterwards placed transversely (distinguished by a stronger outline). 
Each segment is first of all divided by the septum a into an inner and 
an outer cell ; the former produces a part of the inner tissue of the stem, 
the latter the cortex of the stem and a leaf. Leaf-forming shoots ai'ise 
beneath certain leaves, a triangular apical cell z being formed from an outer 
cell of the segment, which then, like v, produces three rows of segments ; 
and each segment here also forms a leaf. (For a more exact description see 
Book II, Mosses.) 
^ Nägeli u. Sch wendener, Das Mikroskop. Leipzig 1869, p. 599 et seq. — Hofmeister, Allge- 
meine Morphologie der Gewebe. Leipzig 1868, Sect. 2. — Pringsheim, Jahrb. für wissen. Bot. 
vol. III. p. 484. — Ditto on Utrictilaria, in Monatsber. der Berliner Akad., Feb. 1869. — Hanstein, Bot. 
Abhandlungen, Bonn 1870, Heft I. — Leitgeb, Botan. Zeitg. 1871, no. 3. — Warming, Recherches sur 
la ramification des Phanerogames. Copenhagen, 1872, p. vi. 
^ Since phenomena of this kind are confined to the flowers and inflorescence of Phanerogams, 
their consideration may for the time be postponed. 
