Bower Studies in the Phytogeny of the Fi tic ales. 307 
The anatomy of the stock is on the same plan as in the preceding genera. 
It is traversed by a dictyostele. In W. polystichoides the foliar gaps are 
relatively narrow, and from the lower region of each two leaf-trace strands 
arise. 1 A distinct involution of the outer surface is found just above the 
insertion of each leaf, similar to those in Struthiopteris , Onoclea , and 
Cystopteris. 
The leaves are densely covered with broad chaffy scales ; these almost 
hide the sori, which form regular series near the margin. Vertical sections 
through them show that, as in other Ferns of this relationship, the vein 
does not terminate in the receptacle, but may pursue a further course towards 
the leaf-margin. This may be quite clearly seen in sections of Woodsia 
obtusa. It is a point of difference from Acrophorus. The receptacle itself 
is only slightly raised above the leaf-surface, and from its base springs the 
indusium ; this consists of usually four overlapping scales, which may be 
separate down to their very base. They are similar in structure and origin 
to the protective scales of the leaf-surface. Upon the receptacle the 
sporangia are seated. They are not numerous. Such evidence as is 
available goes to show that the sorus is essentially a gradate one. This 
conclusion coincides with the observations of Schlumberger (‘Flora’, 1911, 
p. 407, Fig. 13) on W. ilvensis and W. obtusa ; for though he makes no 
mention in his text of the order of succession of the sporangia, his drawings 
show the centrally lying sporangia as the earliest and the most advanced, 
while the peripheral are the lower and smaller. This is also indicated by 
Fig. 42, which represents a drawing of the sorus of Woodsia ilvensis in 
surface view, kindly sent me by Prof. Goebel. 
In my Studies, IV, p. 59, the statements as to the condition of the 
sorus in the genus were rather indefinite. It was stated that 1 some species 
( W. mollis , j. Sm.) suggest that the central sporangia mature first, and the 
peripheral ones later, but this is not borne out by W. obtusa , Torrey, from 
the Edinburgh Garden’. And in a later passage the sorus of the genus was 
held to be a ‘ mixed ’ one. Examination of a large number of sections 
from Woodsia obtusa , of which additional material was obtained from the 
Edinburgh Botanic Garden, has convinced me that the sorus of that species 
is a gradate one. No interpolation of sporangia has been seen. But the 
receptacle is not raised far beyond the general leaf-surface, and the basipetal 
sequence of sporangia is very short (Fig. 41). It thus appears that my 
earlier statements with regard to this genus were incorrect, being based on 
insufficient observation. The sorus is probably a gradate one throughout 
the genus. The sporangia themselves show no special point of interest, and 
have the usual structure of stalk, with three rows of cells. 
Observations have lately been made by Schlumberger on the prothalli 
1 See Schlumberger, Flora, 1911, p. 409, and Fig. 14, where the vascular skeletons of W. 
ilvensis and obtusa are described. Compare also Luerssen, Rab. Krypt.-Fl., vol. iii, p. 498. 
