36 VASCULAR CRYPTOGAMS 



obliquely — not horizontally, as in Salviniaceae — into three rows of seg- 

 ments, until ultimately a convex septum cuts off a triangular apical cell, 

 which at length becomes the tetrahedral archespore. From this is 

 separated the mantle-layer of tapetal cells ; further divisions take place 

 both in these and in the rows of cells of which the wall of the sporange 

 is composed, and the archespore divides by successive bipartitions into 

 sixteen spore-mother-cells, each of which produces four spores in the 

 ordinary way. The pedicel of the sporange consists at first of three rows 

 of cells, the number being subsequently increased by further longitudinal 

 divisions. The tapetal cells become gradually disorganised, and form a 

 granular mucilage, filling up the interstices between the mother-cells of 

 the spores, which is subsequently employed in the production of the 

 epispore or gelatinous envelope of the spore. The differentiation of the 

 two kinds of spore now commences. In the microsporanges all the 

 sixty-four microspores reach maturity, each special mother-cell or rudi- 

 mentary spore becoming invested, while still within the mother-cell, with 

 its permanent cell-wall, while the walls of the sixteen mother-cells dis- 

 appear. In the megasporanges, on the other hand, one of the four 

 special mother-cells in each of the sixteen tetrads displays at first a 

 greater vigour of growth than the other three. Of these sixteen sister- 

 cells fifteen gradually become abortive, only one reaching maturity and 

 developing into a perfect megaspore. During their development and 

 disappearance all the rudimentary spores are furnished with spiny pro- 

 tuberances, by which they are attached to one another. As the mega- 

 spore increases in size its coat becomes hard and brown ; and it is ulti- 

 mately invested by a gelatinous epispore consisting of three distinct 

 layers (fig. i6). The innermost of these is a mucilaginous coat, which 

 is often folded, and ultimately forms a papilla above the apex of the 

 mature spore. Outside this is a thicker layer of a soft prismatic sub- 

 stance, and external again to this a third still thicker but less clearly 

 organised envelope. The two outer layers are wanting at the apex of 

 the spore, where there is a funnel-shaped depression exposing the papilla 

 belonging to the innermost layer of the epispore. Down this funnel the 

 antherozoids pass to impregnate the oosphere within the archegone pro- 

 duced on the prothallium within the apical papilla of the megaspore. 



The processes by which both kinds of spore escape from the very 

 bard shell of the sporocarp are very remarkable. In Pilularia globu- 

 lifera (L.). the ripe sporocarp lies above or beneath the surface of the 

 damp soil. It splits from its apex downwards into four valves, and 

 exudes a tough hyaline mucilage derived from the parenchymatous 

 tissue within each compartment. This mucilage accumulates on the 

 ground ; and into it both kinds of spore escape after the rupture of the 



