39<5 



VASCULAR CRVPTOGAMS. 



Fig. 277. — Development of tlie embryo of h'qutsetum ar- 

 vense (after Hofmeister) ; A archegonium cut through vertically 

 with the embryoy (X200) ; 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 E. arvense, pratense, 

 and variegaium, 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 fiist 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 lacu^iae of 

 the cortical tissue (which are sometimes 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. 



