EQUISETACEyE m 



discs are developed the sporanges, from five to ten on each disc, 

 arising at first as small multicellular projections. The archespore is the 

 terminal cell of a hypodermal row on the under side of the sporophvll, 

 the sporogenous tissue resulting from its division. The mantle-cells are 

 formed in the same way as in Ophioglossaces, but are not so sharply 

 defined. The mother-cells of the spores are connected together in 

 groups of fours or eights, and float freely in the fluid which fills the spo- 

 range. The mode of formation of the spores affords an exceedingly 

 good illustration of the production, by free-cell-formation, of new cells 

 within a mother-cell. When division is about to take place, the proto- 

 plasm first becomes perfectly clear, the nucleus disappears, and a 

 number of granules arrange themselves in the form of a disc. The 

 protoplasm then again becomes turbid, with the exception of two clear 

 spots, one on each side of the disc, which are the rudiments of the 

 fresh nuclei. These, however, after a time again disappear, and their 

 place is taken by four smaller nuclei, each of which is surrounded by 

 a number of the granules which formed a portion of the original disc. 

 Round these nuclei the cell-protoplasm begins now to collect into four 

 separate masses, which gradually become globular ; and these are the 

 special mother-cells of the spores after each has become invested with 

 a ver}- delicate coat of cellulose. This process, which has a remarkable 

 analogy to the formation of the pollen in Flowering Plants, especiallv in 

 Coniferge, does not vary in any essential point from that in the other 

 orders of Vascular Cr\'ptogams ; but it has been followed out with the 

 greatest minuteness and success in Equisetum (limosum, L. ). 



The mature sporange dehisces by a longitudinal fissure on its inner 

 side facing the sporophyll. The mechanism of the bursting is similar 

 to that of the anther of Flowering Plants, and results from the unequal 

 contraction of lignified and of non-lignified portions of the wall, which 

 is furnished with annular or spiral thickenings to its cell-walls. The 

 various coats of the spores are formed while still within the mother-cell. 

 The first formed is the outermost, a non-cuticularised coat capable of 

 swelHng, which becomes gradually detached, and finally splits into two 

 bands, the elaters, which remain attached to the spore only at one point, 

 in the centre of each, where they meet, while the distal ends of each are 

 dilated into a flattened spathulate form. When the spore escapes from 

 the sporange the four elaters are stretched out nearly straight : when 

 moistened they roll up, owing to their unequal lignification, covering up 

 the spore almost entirely, as they did at first before becoming detached. 

 The second coat is more or less cuticularised, and on germination also 

 raises itself in folds from the innermost coat, which is closely applied to 

 the contents of the spore, and is again differentiated into an outer 



