39^ 
VASCULAR CRYPTOGAMS, 
Fig. 277.— Development of the embryo of f.quisetuDi ar- 
vense (after Hofmeister) ; A archegonium cut through vertically 
with the embryo y ( X 200) ; B embryo further developed and 
isolated, b rudiment of a leaf, s apex of the first shoot (X 200) ; 
C vertical section of a lobe of a prothallium / /, with a young 
plant, w its first root, b b' its leaf-sheaths (X 10). 
The first leaf-bearing shoot grows upwards, and forms from ten to fifteen 
internodes with leaf-sheaths ending in three teeth. It soon produces at its 
base a new stronger shoot with four-toothed sheaths (as in F. arvense, pratense, 
and varicgatum, according to Hofmeister), which in turn gives origin to new 
generations of shoots, developing con- 
stantly thicker stems and sheaths with a 
larger number of teeth. Sometimes the 
third or one of the succeeding shoots 
penetrates downwards into the ground, 
forming the first perennial rhizome, which 
again produces from year to year new 
underground rhizomes and ascending leafy 
shoots. 
In order to facilitate the understanding 
of the Mode of Growth of the Stem and 
Leaves, it is necessary to glance in the first 
place at their structure in the mature state. 
Every axis of an Equisetum consists of a 
series of joints (internodes) usually hollow 
and closed at their base by a thin septum. 
Each internode passes upwards into a 
leaf-sheath embracing the next internode, 
the sheath being split at its upper margin 
into three, four, or usually a larger number of teeth. From each tooth of the 
sheath a fibro-vascular bundle runs vertically downwards into the internode as far as 
the next node, parallel with the other bundles of the same internode ; at the lower 
end each bundle splits into two short diverging limbs, by which it unites with the 
two neighbouring bundles of the next lower internode, where they descend into 
it from their sheath-teeth. The joints of the stem and their leaf-sheaths therefore 
alternate ; and since in each joint the arrangement of bundles, leaf-teeth, projecting 
longitudinal ridges, and depressions or furrows, is exactly repeated in the transverse 
section, the different parts of a joint always correspond to the intervals between 
the homologous parts of the next upper and next lower joint. If the internode 
has projecting longitudinal ridges on its surface, one of these always runs down- 
wards from the apex of each leaf-tooth parallel with the others as far as the 
base of the internode; between each pair of leaf-teeth commences a furrow or 
channel, which also continues as far as the base of the internode. The projecting 
ridges lie on the same radii as the fibro-vascular bundles, each of which contains 
an air-canal; the depressions or furrows lie on the same radii as the lacunae of 
the cortical tissue (which are sometim.es wanting), and alternate with the fibro- 
vascular bundles. The branches and roots spring exclusively from within the 
base of the leaf-sheath; and as this forms a whorl, the branches and roots are 
also verticillate. A root may arise beneath the bud of each branch ; both break 
through the leaf-sheath at its base. All the joints of the axis agree in these respects, 
however they may be modified as underground rhizomes, tubers, ascending stems, 
leafy branches, or sporangiferous axes. 
