100 DICTYOTACEiE. iv. 



thread, accompanied by the expansion of the walls into thin membranes. Next, in 

 Punctaria, the bag becomes flattened into a nerveless leaf. In higher groups the 

 tubular or flattened frond is divided into a branching stem, which, however, does not 

 develope any separate leafy organs. In one case (Haliseris) this stem is winged 

 throughout with membrane, or may be described as a midribbed branching frond. 

 Among the most highly developed genera (Zonaria and Padina) the frond shows a 

 tendency to assume a fan-shaped outline, having a definite, subcircular margin at 

 the summit, and gradually widening from the base upwards. Such fronds are 

 usually marked at regular intervals with concentric lines, and are formed of longi- 

 tudinal rows of cells collaterally united in membranes ; the rows diverging as they 

 grow, and new rows of cells being introduced in the interspaces. In many, and 

 perhaps in all, the growing frond is clothed with exceedingly slender, jointed, and 

 often colourless hairs, which sometimes, whilst expanded under water, decompose 

 the rays of light, and cause the frond to display brilliant prismatic colours. These 

 hairs are prolongations of the surface-cells, or issue from their sides, and are 

 probably organs of the same kind as the pencilled fibres already noticed in the 

 Sporochnacece. 



The fructification exhibits considerable diversity of aspect in the various genera, 

 but the characters are of minor value, chiefly relating to the form and position of 

 the masses of fruit. In all, the spores are developed externally, either being formed 

 from the surface-cells, which, when fertilized, stand out prominently from the 

 ordinary cells ; or from those cells immediately beneath the epidermis, in which 

 case the spore-cell bursts through the external coat, carrying it outwards as a 

 separated membrane. Usually each perispore contains but a single sporular mass, 

 but in Padina, four spores are found at maturity in each perispore ; and in 

 Cutleria, eight spores. In some genera the spores are scattered singly over the sur- 

 face of the frond ; but in by far the greater number they are collected into definite 

 spots, or sori, which are round, oblong, or linear, and are either dispersed irregularly 

 over the whole surface, or confined to a certain part of it ; or else ranged in 

 transverse, horizontal, or concentric bands. In some, both scattered and aggregated 

 spores are found on the same individual, or on different individuals of the same 

 species. In such cases, the scattered spores are usually of larger size and paler 

 colour than the aggregated ones, and their contents appear to be difierent. They 

 have sometimes been supposed to be antheridia, but have not, as yet, been examined 

 vnth sufficient care. The spores in most cases are accompanied by barren, jointed 

 hairs, or paranemata^ which appear to be formed from the same parts as the fertile 

 spores, but to have developed into numerous cells. In Stilophora these paranemata 

 compose the greater part of the warts of fructification. In some of the more 

 perfect forms, as in Cutleria and Padina, antheridia have been noticed ; these are 

 sometimes found on the same individuals as the spores, and sometimes on different 

 individuals. 



This Order is of decidedly rare occurrence on the American coast, and scarcely 

 attracts much notice, from the amount of individuals representing the sj)ecies. 



