266 THIRD GROUP. VASCULAR CRYPTOGAMS. 



the innermost layer which is next the axile bundle takes the place to some 

 extent of the pericambium which is wanting in the roots of the Equisetaceae. At 

 the same time this layer is distinguished from the pericambium of the roots of other 

 Cryptogams by the circumstance that the lateral roots originate in it ; in the 

 Equisetaceae, therefore, as in all Cryptogams, the lateral roots spring from the inner 

 layer of the cortical tissue, and as there is no pericambium in the Equisetaceae, the 

 point of origin of the roots is close to the outer vessels of the axile bundle. The cells, 

 each of which is the mother-cell of a lateral root, are formed in strict acropetal 

 succession in the innermost layer of the cortical tissue on the outer margin of the 

 primary vessels. 



The sporangia of the Equisetaceae are outgrowths of peculiarly metamorphosed 

 leaves formed in usually numerous whorls on the summit of ordinary shoots, or of 

 shoots specially destined to this end. An imperfectly developed foliar sheath, the 

 annulus, is first of all formed above the last foliar sheath of the vegetative portion of 

 the fertile axis (Fig. 221 a). The annulus is sometimes more, sometimes less leaf- 

 like in appearance, and above it and below the apex of the growing shoot annular 

 cushions appear in acropetal succession, as in the ordinary formation of the leaves 

 in the Equisetaceae. These cushions do not project much above the surface, and 

 are distinguished from those which give rise to toothed foliar sheaths by the circum- 

 stance, that all the rows of cells in the portion of the axis where they arise are 

 employed to form them, whereas in the case of the toothed foliar sheaths the lower 

 rows of cells help to build up the cortex of the stem. These hemispherical 

 projections are the rudiments of the sporophylls (sporangiophnres], and on each of 

 them a large number of protuberances arise, answering to the teeth of ordinary foliar 

 sheaths ; in this way several whorls of hemispherical projections are formed, lying 

 close one above the other, which grow more rapidly on their outer side, and 

 press against each other and so become polygonal and usually six-sided, while the 

 basal portion of each protuberance remains more slender and forms the stalk of the 

 six-sided peltate disk. The outer surface of the disks is tangential to the axis of the 

 sporangiferous spike ; on the inner side which is towards the axis from five to ten 

 sporangia are produced on each disk. The sporangium in an early stage of develop- 

 ment looks like a small blunt pluricellular wart, and developes exactly in the same 

 way as the sporangium of the Marattiaceae. The mother-cells of the spores are 

 developed from a hypodermal archesporium, while of three outer layers of cells which 

 surround it at first, only the outermost remains at the last as the wall of the sporangium. 

 The spore-mother-cells, adhering to one another in groups of four or eight, float free 

 in a fluid which fills the cavity of the sporangium and has granules distributed in it. 



The spores are formed by division into four parts (repeated bipartition) of their 

 mother-cells, and are tetrahedrally arranged. The ripe sporangium opens by a 

 longitudinal fissure on the side towards the stalk of the peltate disk. The very thin- 

 walled cells of the wall previously form spiral thickening ridges on the dorsal side of 

 the sporangium and annular thickening ridges on the ventral side, and these ridges 

 are formed in E. Itmosum, according to Duval-Jouve, very rapidly just before the 

 dehiscence of the sporangium. The spores of the Equisetaceae have the peculiarity 

 of forming several coats. Each spore forms at first an outer coat which is not 

 cuticularised and is capable of swelling, and this when subsequently split up into two 



