BELESSEMAtJEB. 



of irregular form, without distinct costa, and either homoge- 

 neous, or traversed by branching, obscure and vanishing 

 nerves. The distinction of the frond into stem and leaves, 

 although in some cases, as in Delesseria sanguined, very ob- 

 vious, is nowhere, to my knowledge, absolute ; the stems 

 having, at an early period of growth, been in all cases leaves, 

 and having lost their leafy character by the destruction of 

 the lateral membrane, which never grows again. The costa, 

 continuing to vegetate, throws out from its sides new leafy 

 fronds, and thus the branching often becomes very irregular. 

 This power of the costa to originate new fronds from any 

 part equally exists in such branching plants as Del. alata, 

 which is often converted from a flat and perfectly distichous 

 forked leaf into a dense, bushy tuft, composed of innume- 

 rable similar leaves, springing, without order, each from the 

 midrib of an older leaf. In Del. hypoglossum and D. rusci- 

 folia this proliferous habit is shown in perfection. In these 

 species each frondlet is perfectly simple at all ages, and 

 composition can only take place by new frondlets springing 

 from the midribs of the old. Other species, as D. alata and 

 D. sinuosa, have a double mode of enlargement ; normally by 

 division of the frond, and abnormally by proliferous develop- 

 ment. The cells of which the frond is composed are rarely 

 elongate. In most cases they are twelve-sided, about as long 

 as broad, and heaped together without much order ; but in 

 some they are cubical, and disposed in regular rows, vertical 

 with the surface when the frond is thick. But in no case do 

 they cohere strongly by their ends, so as to form separable 

 filaments. The surface cells are often, but not always, large 

 and flattened, and thus the frond has an areolated appear- 

 ance under a lens. The coccidia are produced on various 

 parts of the frond, and are either formed by a metamorphosis 

 of a leaf (as in D. sanguined], in which case they are pedi- 

 cellated ; or they originate from the midrib, as is common 

 in Delesseria ; or they are scattered over the membrane, as 

 in Nitophyllum and in Delesseria Lyallii. They are usually 

 hemispherical, prominent on one or other side of the frond 

 indifferently, having a membranous pericarp, usually as thick 

 as the frond from which it is developed, and they contain, on 

 a central, basal placenta a tuft of dichotomous threads, with 

 moniliform articulations, whose apical cells, and sometimes 

 all the cells of the filament, are converted into spores, acquir- 

 ing a dark red colour and dense substance. The tetraspores 

 are commonly triangularly parted, but in Plocamium they are 



