THE HIGHER CllYPTOGAMIA. 365 



primary cell of the ligulate process which covers the base 

 of the scale, and the lower one becomes the primary 

 mother-cell of the sporangium (PL LIII, fig. 1). By 

 repeated divisions in all three directions, especially in a 

 longitudinal direction, the latter is soon changed into 

 an oval hillock of cellular tissue, whose longitudinal axis 

 coincides with that of the leaf (PI. LIII, figs. 2, 3). The 

 longitudinal and transverse divisions produced by septa 

 perpendicular to the front surface of the leaf, are more 

 active in each of the new outer cellular layers of the rudi- 

 ment of the fruit, which are formed by septa parallel to 

 the free outer walls of the cells of the upper surface. The 

 young sporangium soon becomes an oval cellular mass at- 

 tached to the leaf by a proportionably small basal surface. 

 The tissue of the leaf which adjoins the place of attach- 

 ment of the sporangium afterwards — when spore-formation 

 begins — overgrows the fruit on all sides, principally above ; 

 it forms a membranous border, reaching far above the 

 sporangium, and is the veil of descriptive botanists (PI. 

 LIII, fig. 5). 



Until shortly before the appearance of this last 

 growth of the base of the leaf, the sporangium con- 

 sists throughout of homogeneous delicate walled cells, 

 which now beoin to be differentiated into three different 

 sorts of tissue. The two outermost cellular layers assume 

 more and more a tabular shape, and become the capsule 

 wall. The interior divides into groups of clelicate-walled 

 cells in close connexion with one another — the primary 

 mother-cells of the spores — and into plates separating 

 these groups of cells from one another, and formed each of 

 two layers of cells whose intercellular cavities contain air. 

 The cells of the wall of the sporangium, as also those of 

 the tissue destined to produce the reproductive cells, con- 

 tinue to multiply by division for some time longer. The 

 cells of the plates which divide the portions of that tissue 

 from one another keep pace with the increase in size of the 

 sporangium by expansion of their walls (PI. LIII, fig. 4). 



At last the spore-mother -cells, separate from one another, 

 and assume a globular form (PI. LIII, figs. 6, 7, 8). In 

 the sporangia intended to form small spores, more generations 



