496 



BOTANY 



PART II 



peculiar form and hygroscopic movements the peristome causes a. gradual dis- 

 semination of the spores from the capsule. 



Variations in the form of the capsule, peristome, operculum, and calyptra afford 

 the most irr-portant means of distinguishing the different genera. The Bryales 

 are divided into two sub-orders, according to the position of the archegonia or of 

 the sporogonia developed from them. 



(a) In the Acrocarpi the archegonia, and consequently the sporogonia, are 

 terminal on the main axis. Mnium undulatum (Fig. 456) and hornum, Poly- 

 trichum commune (Fig. 454), and Funaria hygrometrica are common examples. 

 Schistostega osmundacea, a moss living in caves, has fertile shoots, which have 

 spirally-arranged leaves and bear stalked capsules devoid of peristomes, and also 

 other shoots that are sterile, with two rows of leaves (Fig. 455). The protonema 

 of this species is peculiarly constructed and gives out an emerald phosphorescent 





FIG. 460. Mnium hornum. A, Capsule with upper portion of seta ; ap, apophysis ; p, peristome: 

 d, the separated operculum. B, Three teeth of the outer peristome seen from the outside ; an, 

 annulus. C, Inner peristome seen from the inside ; w, broader cilia ; h, narrower cilia. 

 (A x 4 ; B, C x 60.) 



light. In some minute Mosses (Archidium, Phascum, Pleuridium] the sporo- 

 gonium is considerably simplified, the formation of operculum, annulus, and 

 peristome being suppressed and the spores set free by decay of the capsule. 



(6) In the Pleurocarpi the growth of the main axis is unlimited, and the 

 archegonia with their sporogonia arise on short, lateral branches (Fig. 457). In 

 this group are included numerous, usually profusely-branched species of large 

 Mosses belonging to the families Neckeraceae and Hypnaceae, which are among 

 the most conspicuous mosses of our woods, and also the submerged Water Moss, 

 Fontinalis antipyretica. 



III. PTERIDOPHYTA (VASCULAR CRYPTOGAMS) ( 



1, 92, 112-131 



The Pteridophytes include the Ferns, Water-Ferns, Horse-tails, 

 and Club Mosses, and represent the most highly developed Crypto- 

 gams. In the development of the plants forming this group, as in the 

 Bryophyta, a distinct alternation of generations is exhibited. The 



