24 Bower.—Studies in the Phytogeny of the Filicales . VIP 
the state of the pinnule with sterile margin. Two of these are shown 
in Fig. 2 i, i, ii. In the latter both indusia are present and the com¬ 
missure ; but the receptacle is very narrow, and bears only a single spo¬ 
rangium. In i the receptacle, sporangia, and commissure are all absent, 
though the lower indusium is still represented by hair-like structures. The 
next step is the absence of til? lower indusium also, giving the sterile 
condition frequently found with upper indusium but without receptacle 
or commissure, as noted by Luerssen. 1 
Paesia. 
Paesia has always been associated by systematists with Pteridium ; 
in fact the latter has been included in the former genus. 2 The similarity 
is based partly on habit, but chiefly upon the character of the sorus. 
The stelar anatomy is simpler than that of Pteridium. It is already 
known for P . scaberula. Gwynne-Vaughan has included it in his list of 
typical solenbstelic Ferns. 3 Material of P. viscosa was available from 
Jamaica through the kindness of Mr. Harris. This species bears ample 
leaves upon its creeping and bifurcating rhizome, and, as in P. scaberula, 
there is a typical solenostele and an undivided leaf-trace. The dermal 
appendages in both are hairs, as they are also in Pteridium , with which the 
affinity has always been recognized. 
The sorus of P. viscosa appears tucked away under the margin of 
the pinnule, and does not usually extend far without interruptions. 
Several veins may run out to each length of it, and they are connected 
at their distal ends by a receptacular commissure as in Pteridium . The 
material did not suffice for demonstrating the earliest stages of the sorus, 
but from comparison of sections of P. viscosa with other related Ferns, 
the receptacle was no doubt of marginal origin. The upper (adaxial) in¬ 
dusium is the larger, and consists of about three layers of cells, thinning 
out at the margin to a single layer. The lower (abaxial) consists of only 
a single layer. It arises later than the upper, and is overlapped by it 
(Fig. 22, B, c). Sometimes it may be altogether absent, as is noted 
in the specific description in the ‘ Synopsis Filicum ’ (p. 163). This is the 
case in Fig. 22, A, and it may be regarded as an important comparative 
step towards the state seen in Pteris. The first sporangium usually appears 
on the side of the receptacle nearest to the indusium, and it is followed by 
a second on the adaxial side. But there is no definite succession, and the 
number of sporangia is small. 
Associated with the sporangia are hairs, but they are not constant. 
They are multicellular, and the distal cell, though not glandular, is often 
enlarged and densely protoplasmic (Fig. 22, c). Their appearance in 
early stages suggests that they may represent abortive sporangia, with 
1 1 . c., p. 104. 2 Syn. Fil., p. 162, 3 Lc., p. 691, 
