ON THE DEVELOPMENT OF THE THECA. 



171 



sally supposed, but by the addition of fresh matter. At the same time the style 

 becomes of a red or brown colour, of a rigid texture, and never increases in size 

 after the opening of its canal. In Funaria hygrometrica the pistillum elongates 

 considerably before the base has increased in diameter, to allow of the rapid 

 growth of the oblong or fusiform mass within, which now occupies its whole 

 length from the apex immediately beneath the hardened style to the very base, 

 and even beyond, having pushed its conical extremity deeper into the tissue, until 

 at last it has actually penetrated the branch itself. After the pistillum has 

 attained a considerable length, its base increases in diameter without a corre- 

 sponding increase of the central body, so that a space is left between the two. 

 Very shortly the pistillum separates transversely below the dilated portion, and is 

 supported on the apex of what may now be called the seta, by the more rapid elonga- 

 tion of which the separation has been caused. At this period may be observed a 

 sheath of elastic gummy secretion embracing the base of the seta, immediately oppo- 

 site the point of separation between the upper part of the pistillum (now called 

 calyptra) and the base, which has received the name of Vaginula. This sheath of 

 mucus gradually becomes solid and cellular, and by its connexion with the vaginula 

 and its firm embrace of the seta, serves to secure the latter in its cavity. 



" A period of a month or more follows the separation of the calyptra without 

 any further change taking place than the gradual elongation of the seta. In some 

 instances, as in Encalypta vulgaris, Tortula ruralis, and many more, three or four 

 months are occupied by this process. The seta elongates by the addition of new 

 matter at the apex, where it is always of a more delicate texture than nearer the 

 base. The cells are also more crowded, less distinct in their outline, and have as 

 yet no cavity. The further you examine from the apex, the more decidedly does 

 the tissue become cellular, until it has arrived at maturity, when the cells are con- 

 siderably elongated. After attaining a length varying in each species according 

 to circumstances, the seta gradually enlarges in diameter at the apex, and imper- 

 ceptibly assumes the form of the theca. A section of the dilated apex, if made at 

 an early period, will exhibit a central portion of a cortical layer, only differing 

 from the structure of the seta itself by being more distinctly defined. As the theca 

 advances towards maturity, the cortical layer gradually recedes from the central 

 axis, but is still connected with it by little transverse fibres, or rather strings of 

 cells, which pass from one surface to the other without any apparent arrangement. 

 The axis, or columella as it is now termed, is supported on a pedicel, which is con- 

 tinuous with the central tissue of the seta, whilst the outer layer, or true theca, is 

 an expansion of the external layer of the seta. Surrounding the theca, near the 

 apex, is a faint line, which indicates the situation of a transverse dehiscence to 

 take place at the perfect maturity of the theca. The portion above this line 

 varies considerably in figure, and is called the lid, or operculum. The ring, or 

 orifice of the theca formed by the fall of the operculum, is called the mouth, or 

 stoma. It is necessary to name these parts in this stage of the development, to 

 explain clearly the succeeding, steps of the process. 



z 2 



