LOXSOMACEAE 571 
This is biologically probable, since the successive development has the 
advantage of producing a large spore-output, while the physiological drain 
would thus be spread uniformly over a long period of time. 
LOXSOMACEAE. 
This family is represented only by the single species Loxwsoma Cunning- 
Aamt, Br., native in New Zealand. It unites in itself characters of several 
distinct tribes of Ferns, and as a consequence its systematic position has 
been difficult to fix. It has the habit of a coriaceous Diécksonia or of a 
Davaltia, and a sorus like Zrichomanes; but it differs from all of these 
in having a dehiscence of the sporangia in a median plane. This combina- 
tion of characters has led to its being variously placed by different 
systematists. It is best regarded as the sole representative of a distinct 
tribe, and its natural position appears to be about the limit between the 
Simplices and the Gradatae, in a phyletic line which leads towards the 
Hymenophyllaceae and Dicksonieae. 
L. Cunninghami is an elegant Fern, with elongated, creeping rhizome, 
bearing irregularly disposed roots, and at intervals of about an inch firm 
coriaceous leaves, one to two feet high, which are glabrous, twice or 
thrice pinnate, and glaucous beneath. The sori are marginal, each seated 
upon the ending of one of the simple or branched veins. There is a basal 
cup-shaped indusium, with an entire rim: it surrounds the receptacle, 
which is columnar, and bears numerous fluffy hairs interspersed among 
sporangia, which originate in a basipetal succession. The whole appearance 
of the Fern is very like some of the creeping species of Dicksonia or 
Davaltia. 
I am not aware of any fossils having been attributed to this family. 
SPORE-PRODUCING MEMBERS. 
A vertical section through a sorus of medium age shows, as in Fig. 320 £, 
the short receptacle, sporangia, and hairs, all of which are included within 
the cup-like indusium; there is an obvious basipetal sequence of the 
sporangia. The orientation of the sporangia relatively to the centre of 
the sorus is constant, on the Gleicheniaceous type. The pear-shaped 
sporangia, which rise obliquely upwards, have a complete annulus, as is 
shown in Fig. 320D, which represents the “peripheral” face; but though © ~ 
the complete series of cells of the ring can usually be traced, the induration 
of the walls is very unequal; commonly the cells of the distal half are 
enlarged, and their walls thickened; these are mechanically functional, 
while the lower part may be composed of thinner-walled cells, sometimes 
slightly or irregularly thickened, but usually not differing from the rest 
of the cells of the wall, except in their form and arrangement. This is 
shown in side view in Fig. 320c. If we compare Figs. c and p with drawings 
