Bower. — Studies in the Phytogeny of the Pi li cates. 291 
held as some indication that shifting of its position had occurred. It is, on 
the other hand, quite possible that the Cyatheaceous type of dehiscence may 
have existed ab initio . This, however, seems to me to be the less probable 
reading of the facts. 
Taking all the points of correspondence and of difference into account, 
it appears probable that Gleichenia and Lophosoria are genera which are 
descendants of a common stock which had a superficial sorus, of the type of 
the Simplices ; that in certain of the forms a departure was made from the 
originally radiate uniseriate type by formation of sporangia in the centre 
of the sorus, as in G. linearis and pectinata , the latter of which reached the 
limit of crowding of the sorus which could secure effectiveness of dehiscence 
by the median rupture ; that this difficulty was avoided by another 
related stock, represented in its simplest form by Lophosoria , in which, 
either as an original character, or more probably as a result of later adapta- 
tion, the lateral dehiscence is now seen. 
Spore and Prothallus. 
The mature spore of Lophosoria is a very characteristic one. It is 
tetrahedral, and shaped like a kettle-drum. There are three flattened faces, 
separated by lines which converge to the central apex and marked by 
irregular spots. These represent the skin of the drum. The margin of the 
drum-head is expanded into- a projecting circular band, while the rest of the 
rounded body of the spore is covered by a thick wall, marked by minute 
rounded bosses (Fig. 34). 
On germination the rupture takes place along the three converging 
lines, and the three apical flaps of the outer wall come apart. The prothallus 
is at first filamentous, and in crowded cultures may continue so for some 
length. But sooner or later the apex widens out into a spathulate form, 
with its lobes ill-defined and unequal, as is usual in Alsophila (Fig. 35). My 
cultures have progressed to the stage of producing antheridia, which are 
of a usual type. They rupture by the extrusion of a single cell. Unfor- 
tunately, the first cultures at this stage damped off. But attempts are being 
made to raise fresh cultures from spores kindly supplied from Jamaica 
by Mr. Harris. A fuller statement on the gametophyte and observations 
on the young sporophyte will have to be deferred to a later communication. 
Morphological Discussion. 
A considerable number of characters have been mentioned in the 
above pages, according to which the Fern described as Alsophila ( Lopho -* 
sona) pruinata occupies a peculiar position of aloofness ; characters which 
were for the most part unknown to Sir William Hooker, or at least not 
regarded by him as important when he merged it as a species of Alsophila . 
