MORPHOLOGY OF MEMBERS. 
Point, never from those parts of the stem which already consist of fully differentiated 
tissues. In Characese, Muscinese, &c., before or during the first divisions of their 
segments, the leaves become visible close beneath the growing point as protuber- 
ances, the outer portion constituting an apical cell, from the segments of which a 
leaf is built up. In Vascular Cryptogams a many-celled cone of growth often over- 
tops the youngest rudiment of a leaf, as in strong Equiseium buds, Salvinia, many 
Ferns and Selaginellese. In Phanerogams (Figs. 117, 118, 119) this is general^ ; in 
them the rudiment of the leaf does not begin with an apical cell projecting from 
the cone of growth, as in Cryptogams, but a rounded or broad cushion is formed, 
which from its very first origin consists of numerous small merismatic cells. 
(4) The Leaves are always Exogenous Formations, i. e. the rudiment of the 
leaf never has its origin exclusively in the interior of the tissue of the stem, and 
is never covered by layers of tissue of the stem which take no part in its formation, 
Fig. 117. — Terminal region of two primary shoots of maize. 
Apex of the very small-celled cone of growth, out of whicli the 
leaves b, b' , b'' , b'" arise as multicellular protuberances, whicli 
soon embrace the stem, and envelope it and the younger leaves 
like a sheath. In the axil of the third youngest leaf b" the young- 
est rudiment of a branchlet is visible as a roundish protuberance. 
Fig. 118.— Longitudinal section through the apical region of the 
primary stem of the sunflov/er, immediately before the formation of 
the flowers ; j apex of the broad growing point ; b b the youngest 
leaves ; r cortex ; 7n pith. 
as is the case with roots and many endogenous shoots. In Cryptogams it is usually 
a single superficial cell (/. e. superficial before the differentiation of the epidermis) 
which forms the foliar protuberance. In Phanerogams a mass of tissue bulges 
out as the rudiment of the leaf, and consists of a luxuriant growth of the periblem 
covered by dermatogen (Sect. 19, Fig. 113, p. 147). By this means the leaf is at 
once distinguished from the hair even in its most rudimentary state. The hair is an 
outgrowth of the epidermis; but since in Phanerogams the primordial epidermis 
or dermatogen covers the whole of the growing point above the leaves, hairs may 
also spring up higher in position than the youngest leaves, from single cells 
^ [Warming however remarks (Ramification des Phanerogames, p. iii) that the growing point 
may have the most various forms, from that of a rather acute cone, as in Graminese, Amaranthus, 
and Platitago, to that of a cup-shaped depression, e. g. Digitalis, and that the form may differ even in 
species belonging to the same genus; thus in Digitalis lutea it is convex, in D. parviflora con- 
cave.] 
