J. BURTON ON THE REPRODUCTION OF MOSSES AND FERNS. 5 



Taking now a fern as popularly understood, it is unnecessary 

 to attempt any description of the plant, it being so well known. 

 Almost any common species will answer our purpose — for 

 example, the male fern or the common bracken. On some part 

 of the leaf, normal or modified, are found the well-known spor- 

 angia or spore cases. They are disposed in a great variety of 

 ways, according to the species, — sometimes collected in groups, 

 either covered by a membrane called the " indusium," or without 

 it ; or arranged along the edge of the leaf, or along the sides of 

 the veins. The form of the sporangium La very similar in all the 

 species. It consists of a membranous pouch or bag, somewhat 

 pear-shaped and flattened, and round the edge or in a circle at 

 the top is a ring of cells, the annulus, which, when the structure 

 is ripe, and on suitable conditions sup- rvening, breaks, and tears 

 the bag, releasing and scattering the spores. The shape of the 

 spores which are formed from the mother-cells is well known, 

 they being amongst the commonest of microscopic objects. In 

 most species they are brown, but some are green owing to the 

 presence of chlorophyll. The vitality of the former endures for 

 a long period, but the latter will not germinate unless sown when 

 fresh. Osmunda, the so-called flowering fern, has spores of this 

 latter type. For experimental purposes the spores may be thinly 

 sown on small pieces of flower-pot, which should be placed in a 

 saucer with a little water in it, and covered with a glass ; but in 

 this way it is scarcely possible to obtain the full development, as 

 would be the case if the sowing were made on damp earth or 

 sand. In a few days the outer tough coat bursts, and growth 

 commences, much as in the case of the moss spores already 

 described. In some species of ferns for a considerable time only 

 a filament of cells is formed, which at last, however, broadens 

 out into a leaf-like structure. In Osmunda the expansion is 

 formed at once without any preliminary ti lament. This structure 

 is the prothallus, and on it are formed the sexual reproductive 

 organs of the fern. A portion in the centre becomes thicker 

 than the rest, which consists of one layer of cells only. The 

 rhizoids or root-hairs usually spring from this part, which is 

 known as the " cushion." The antheridia may arise on almost 

 any part of the prothallus ; they consist of a ring of cells and one 

 forming a lid, and contain the spermatozoids. In the ferns the 

 spermatozoon is a coiled filament something like a corkscrew? 

 with several cilia at one end, by the aid of which it moves 

 through water. The archegonia, the female organs, are formed 



