104 Davie, — The Development of the Sorus and Sporangium 
stalk of the sorus and ends as a fan below the apex of the wide receptacle. 
Through the base of the stalk this tracheidal system is continuous with the 
series of tracheides in the vascular strand of the vein upon which the sorus 
is inserted (cf. Annals of Botany, xxvi, PL XXIX, Fig. 13). 
Sporangia appear upon the receptacle as soon as it begins to lengthen 
(Fig. 2). The first sporangium occurs in varying positions on the surface — 
sometimes near the junction of the large indusial flap with the receptacle 
(Fig. 3) ; sometimes near the edge of the reduced flap (Fig. 2) ; sometimes 
midway between these positions. 
The first sporangium is rapidly succeeded by others, which arise close 
to it. Two sporangia of approximately the same age sometimes occupy 
positions near the apex of the receptacle, while others very slightly younger 
appear nearer to its margins (Fig. 4). 
A comparison of the condition shown in Fig. 4 with that in Text-fig. 1, in 
which the oldest sporangia occupy the summit of the receptacle, while young 
sporangia appear at the margins, leads us to conclude that the sequence is 
in the main basipetal, but that the sporangia succeed one another rapidly. 
In Text-fig. 1 the youngest sporangia figured are at the apex of the 
receptacle, among the stalks of the oldest. This mixed condition of the 
mature sorus was figured in Ann. of Bot., xxvi, PI. XXIX, Figs. 13, 14, and 
15. The suggestion made in the earlier paper (ibid., p. 254) that the sorus 
is of a mixed type upon a Gradate receptacle is confirmed by the details 
shown in Fig. 4 and Text-fig. 1. The sequence of sporangia shown in these 
figures proves that the succession of the earliest sporangia is essentially 
basipetal. 
Development of the Sporangium. 
The earliest stages of the development of the sporangium are figured in 
Text-fig. 2, a-i. The cell which becomes a sporangium is often wedge- 
shaped (a). The first wall may be transverse (a and b) or oblique (c and d). 
The oblique wall more frequently occurs, to judge by the condition of various 
later stages (g and h), f suggests a later condition of the type shown in 
b. Where the first wall is transverse the one which immediately succeeds it 
is oblique ( e and f), and this second oblique wall commonly meets the first 
at its junction with the lateral wall (e and f). Where the first wall is 
oblique, it may meet the lateral wall at its junction with one of the walls 
forming the wedge-shaped base of the cell (g and h ) ; it may meet the lateral 
wall about half-way down its length (d), or it may meet one of the basal 
walls (c), A wall next cuts the oblique wall at right angles (g), and that 
which succeeds this is parallel to the first oblique wall (h). In z is shown 
the central cell of the capsule fully formed, while the cells of the stalk 
are definitely delimited. The later stages in the development of the 
sporangium and the mature sporangium itself have already been described 
(loc. cit., p. 254). The mature sporangium is long-stalked, and has an 
