XXXVI FIRST PRINCIPLES OF BOTANY. 



532. The part where the stock of the theca is united with its side is called the 

 annulus. 



533. These theca? may be considered minute leaves, having the same gyrate 

 mode of developement as the ordinary leaves of the tribe ; their stalk the petiole, 

 the annulus the midrib, and the theca itself the lamina, the edges of which are 

 united. 



534. They would therefore be analogous to carpella, if it appeared that they were 

 influenced by the action of any vivifying matter. 



535. Mosses are increased by sporules (529), contained within an urn or theca, 

 placed at the apex of a stalk or seta, bearing on its summit a kind of loose hood,- 

 called a calyptra, and closed by a lid or operculum. 



536. The inside of the theca has a central axis or columella, and the orifice be- 

 neath the operculum is closed by teeth-like processes, or a membrane, called the 

 peristomium. 



537. The number of the teeth of the peristomium is always some multiple of four. 



538. The calyptra originally grew from the base of the stalk ; but when the stalk 

 elongated, the calyptra was torn away from its base, and carried up, surrounding the 

 theca. 



539. The calyptra may be understood to be a convolute leaf; the operculum, 

 another ; the peristomium, one or more whorls of minute flat leaves ; and the theca 

 itself to be the excavated distended apex of the stalk, the cellular substance of which 

 separates in the form of sporules. 



540. There are also in mosses organs, called anthers by some, which do not ap- 

 pear analogous to the stamina of flowering plants, and the nature of which has 

 not been demonstrated. 



541. Lichens are propagated by sporules, included within little membranous 

 cases, which lie within a denuded portion of their own central substance, called the 

 scutellum, apothecium, or shield. 



542. Alg^: increase by sporules, which are usually formed by a separation of cel- 

 lular tissue, within the substance of the plants themselves. 



543. Fungi have a similar mode of propagation. In some of the most highly de- 

 veloped of the tribe, the part in which the sporules lie is distinct in appearance from 

 the rest, and called the hymenium. 



