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 Loxsoma 

 hami, 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 Dicksonia or of a 

 Davallia. and a sorus like Trichomanes ; 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 

 Davallia. 



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 E, 

 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. 3201), 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. 3200. If we compare Figs, c and D with drawings 



