Bower.—Studies in the Phytogeny of the Filicales . VII. 47 
Acrostichum , L. (1737). 
It is thus seen that the fusion-sorus may be considerably widened in 
certain species of Pteris , of which the Pteris- nature has never been in 
doubt. These may be held to prefigure other cases in which the Pteris- 
affinity is less obvious. One of them is the Fern designated Acrostichum 
praestantissimum , Bory, which is closely related to Acrostichum aureum , 
L. It is a very local West Indian Fern, figured in Hooker’s ‘ Garden Ferns 
Plate 58. Its habit is rather coarse, with a thick upright stock, simply 
pinnate leaves, and a reticulate venation of the Litobrochia- type. This 
has suggested a comparison especially with P. ( Litobrochia ) splendens. 
The leaves are dimorphic, and 
many specimens show in the fertile 
leaves the whole lower surface 
covered with sporangia, as in 
A. aureum . But in other speci¬ 
mens the sorus extends only part 
way from the margin to the midrib. 
This was noted by F^e, who is 
quoted on the point by Sir W. 
Hooker. The latter remarks that 
‘ there is in that state a distinct 
narrow continuous involucre, as in 
Pteris , closely covering the sori ’; 
and it is shown in his Fig. 3, PI. 58. 
This comparison has recently been 
revived by Frau Schumann, 1 who 
indicates specially the relation to 
P. splendens , and has added many 
facts bearing on the comparison. 
Conditions linking the fully 
Acrostichoid state with the Pteris - 
type of sorus may be found by 
examining pinnae of A. praestan¬ 
tissimum from the apex down- Acrostichum praestantissimum , from the apex 
. downwards, showing widening of the Pterid sorus. 
wards. It is held on grounds ( x 20.) 
of anatomy, and also of general 
morphological comparison, that the apex and base of the leaf show re¬ 
latively primitive features, while the middle region is phyletically advanced 
as compared with them. If this be true, a basipetal sequence of sections 
from the tip would progress from the more primitive to the derivative 
region. Small pieces of herbarium material were available from Kew and 
the British Museum, and serial sections showed the essential points 
1 Flora, 1915, pp* 220, 243. 
Fig. 35. a-c. Successive sections of a pinna of 
