404 



VA SC ULAR CRYPTOGA MS . 



B). The three coats may be easily distinguished even in the quite fresh spore 

 when placed in distilled water (A), (in the case of J^. Umosiini), the outer one 

 (i) being colourless, the second (2) light blue, and the third (3) yellowish. As 

 the development advances, the outer coat is separated like a loose investment from 

 the body of the spore (C, d, e), and at the same time its division into elaters is 

 first indicated. The optical longitudinal section shows that the spiral thickening- 

 bands of this coat are separated only by very narrow spaces of thin membrane (Z), 

 E)\ these at length entirely disappear, and, when the surrounding air is dry, the 

 thicker parts separate from one another as spiral bands, forming when unrolled 

 a four-armed cross ; they are united by their centre, and attached there to the 

 second coat. It is probably this spot which may be recognised even in the 

 unripe spore in the form of an umbilical thickening {n in A and B). In the 

 fully developed elaters an external very thin cuticularised layer may be distin- 

 guished. They are extremely hygroscopic ; when the air is damp they are rolled 

 round the spore, but when dry are again unrolled. When this alternation takes 



Fig. 286.— Development of the spores of Jiqiiisetttm limosum (x8oo) ; A unripe spore with three coats just placed 

 in water; S the same after two or three minutes in water, the outer coat having become separated, a large vacuole 

 IS seen by the side of the nucleus ; C commencement of the formation of the elaters on the outer coat <> (=i in Figs. 

 A and B); D, E the same stage of development in optical section after lying twelve hours in glycerine, e the outer coat ; 

 2, 3, the inner coats separated from one another ; F the outer coat split into spiral elaters, coloured a beautiful blue by 

 Schultz's solution. 



place rapidly (as when lightly breathed on under the microscope), the spores are set 

 in active motion by the bendings of the elaters. If spores, the outer coat of which 

 has not yet become split up into elaters. but which already show the corresponding 

 differentiations {D, E), are allowed to lie for some time in glycerine, the spore 

 contracts considerably, surrounded by its inner coat, while the second cuticu- 

 larised coat raises itself from the former in folds. The inner coat is differentiated into 

 a granular cuticularised exospore, and an endospore of cellulose. 



Very little need be said about the Classification of Equisetaceae, as all existing forms 

 are so nearly related to one another that they may be included in a single genus, Equi- 

 setum. Even the Equisetaceae of earlier geological periods, the Calomites^ show, in the 

 little that is still discernible of their organisation, the closest agreement with existing 

 forms. 



The Hahit of the Equisetaceae is, like their morphological structure, of a very 

 characteristic kind. In all the plant is perennial by means of creeping underground 

 rhizomes, from which ascending aerial shoots rise annually, mostly lasting only for one 



