INTRODUCTION. 
489 
where a single cell (not, however, of preponderating size) occupies the apex, and the 
arrangement of the superficial cells of the ptmctum vegetatiojiis appears to point to it 
as the primary mother-cell, it is nevertheless by no means to be assumed that all the 
cells, and especially the internal mass of the primary meristem, have proceeded from 
it. The primary meristem of the punctum vegetationis consists of a large number of 
usually very small cells, more or less evidently disposed in concentric layers ; an 
outer single layer, the dermaiogen, may be recognised in Angiosperms as the imme- 
diate continuation of the epidermis of the older parts, and is continuous even over 
the apex of the punctum vegetationis. Beneath it Hes a second meristematic tissue, 
[the periblem\ consisting usually of a few layers of cells, which covers the apex and 
passes lower down into the cortex ; this envelopes a third inner mass of tissue, [the 
plerome^ terminating beneath the apex as a single cell ^ [Hippuris, Sic.) or as a group 
of cells ; and out of it proceeds either an axial fibro-vascular body (in roots, and in 
the stems of water-plants), or the descending Hmb of the fibro-vascular bundles. In 
harmony with this the root-cap does not proceed, as in Cryptogams, from transverse 
divisions of an apical cell, but arises, on the contrary, in Gymnosperms from a 
luxuriant growth of the layers of periblem of the root and from their splitdng away 
towards the apex, and in Angiosperms from a similar process in the dermatogen, 
or from a special meristematic layer the caJyptrogen ^. Even the first rudiments of 
lateral structures, leaves, shoots, and roots, cannot be traced back in Phanerogams 
to a single cell in the same sense as in Cryptogams. They are first observable as 
protuberances consisting of a few or a larger number of small cells ; the protuberance 
which is to form a shoot or a leaf shows, even when it first begins to swell, an inner 
mass of tissue which is connected with the periblem of the generating vegetative 
cone, and is covered over by a continuation of the dermatogen. 
The normal Mode of Branching at the growing end of the shoot, leaves, and 
roots, is, with few exceptions, monopodial : the generating axis continues to grow 
as such, and produces lateral members (shoots, lateral leaf-branchings, lateral roots) 
beneath its apex. Some cymose inflorescences appear however to be the result of 
dichotomous branching, and it is possible that in the Cycadese also the branching 
of the stem and leaves may be dichotomous. The monopodial branching of the 
axes is usually axillary ; e. the new rudiments of shoots appear above the median 
plane of very young (but not necessarily the youngest) leaves, in the angle which 
they form with the shoot, or somewhat above it. In Gymnosperms every axil of 
a leaf does not usually produce a shoot ; sometimes (in Cycadeae), the branching 
of the stem, as in many Filicinese, is reduced to a minimum. In Angiosperms, on 
the contrary, it is the rule that every axil of a foliage-leaf [i. e. one not belonging to 
the flower) produces a lateral shoot (sometimes even several side by side or one 
above another); but commonly the axillary buds, once formed, are inactive, or 
develope only at later periods of vegetation. In addition to the above-mentioned 
^ As in so many other respects, here also Isoetes shows an affinity to Phanerogams, as is 
evident from Nägeli and Schwendener's researches on the apical growth of roots. (Compare Nägeli's 
Beiträgen, 1867, Heft. IV. p. 136.) 
2 See Hanstein, Bot, Abhandl. Heft I, and Reinke, Göttinger Nachr. 1871, p. 533. [Janczewski, 
L'accroissement terminal des Racines, Mem. soc. nat. de Sei. de Cherbourg, 1874, and Ann. d. Sei. 
nat. ser. 5, t. XX.] 
