EQUISETINEAE. 



267 



spiral bands forms the so-called elaters ; soon after a second coat and then a third 

 make their appearance. The three lie at first close one on the other like layers 

 (shells) of one coat. But if the spore is placed in water the outer coat swells and 

 rises up from off the others (Fig. 222 B). Even when the spore is quite fresh and is 

 just placed in distilled water the three coats can be readily distinguished (Fig. 222 A\ 

 for the outer (i) is colourless, the second (2) is a light blue, the third (3) is yellowish, 

 {E. limosuvi). As the spore developes the outer coat separates like a loose garment 

 from the body of the spore (C d^ e), and then appear the first signs of the formation 

 of elaters. An optical longitudinal section shows that the spiral thickening bands of 



Fig. 222. Development of the spores of Eqniscluiii limosntii, 

 magn. 800 times. A unripe spore with three coats just placed in 

 water. B the same after lying two or three minutes in water, the 

 outer coat ha\'ing become detached ; a large vacuole appears close 

 to the nucleus. C beginning of the formation of elaters on the 

 outer coat e=\ in Figs. A and B. D, E the same stage of devel- 

 opment in optical section after lying twelve hours in glycerine ; 

 e the coat which forms the elaters, 2 and 3 the inner coats separated 

 from one another. F the outer coat split into spirally-twisted 

 elaters, which are coloured a beautiful blue by Schultze's solution. 



Fig. 221. Equisetiiui Telfnattja. A the upper part of a fertile stem with the lower half of the sporangiferous spike ; 

 * the leaf-sheath, a the annulus, x the stalks of the peltate scales which have been cut off, y transverse section of the 

 axis of the spike. B peltate scales (sporophylls) in different positions and slightly magnified ; st the stalk, s the peltate 

 scale, jf the sporangia. A natural size, B slightly magnified. 



this coat are only separated by very narrow and thin portions of membrane {D, E). 

 These thin strips at length disappear, and the thicker parts separate from one 

 another, if the environment is dry, as two spiral bands. These two bands form a 

 four-armed cross when unrolled, and are narrower in the centre where they are 

 attached to the second coat ; it is this point of attachment probably which is seen in 

 the unripe spore as an umbilical thickening («, A, B). An outer very thin cuticu- 

 larised layer may be distinguished on the developed elaters, which are more than 

 usually hygroscopic, rolling themselves round the spore when the air is damp and 

 unrolling again as the air becomes drier ; if alternation of these conditions is rapidly 



