132 The Microscope, 



present, are much smaller than the others, and arranged in> 

 several layers, thus constituting the elements of an epiderm and 

 midrib. The midrib, or costa, sometimes extends beyond the 

 point of the leaf, terminating in an awn or bristle. In some 

 species (particularly among the Hypnums) there are two costa?^ 

 but in such cases they are usually imperfectly developed and do 

 not extend to the end of the leaf. In some genera, notably 

 Thelia and Thuidium, the leaves are studded with papillse, some- 

 times simple, sometimes two-lobed at their apex. 



The branching of the stems of mosses appears to be " neither- 

 dichotomous nor axillary; the number of lateral shoots is 

 always much smaller than that of the leaves. When the pri- 

 mary shoot produces a so-called ' flower ' at its apex, a lateral 

 shoot situated beneath it not unfrequently displays a more- 

 vigorous growth of a monopodial character, and is then termed 

 an innovation." Prolification, the prolongation of the stem by 

 the continued growth of the bud within and above the male 

 " flower," is a very common occurrence in Polytrkhum, and some- 

 times seen also in Atrichum, etc. 



The propagation of mosses takes place in two ways ; sexually, 

 from spores ; and asexually, that is by a vegetative propagation,, 

 which is of several kinds : 1st, by innovation, a process of re- 

 newal at the apex, while the older parts die off behind ; 2d, by 

 means of gemmae, stolons, or detached buds, (in Tetraphis pellu- 

 cida the leafy axis frequently bears a terminal cup-shaped re- 

 ceptacle, containing many lentiform, stalked gemmge; these- 

 separate spontaneously, and give rise to a kind of protonema,. 

 and upon this buds arise, from which leafy axes are developed). 

 3d, by the non-sexual production of a thallus or protonema. 

 This is sometimes produced from detached leaves, and can also- 

 be produced from the rhizoids if placed in the light and kept 

 moist. I have a tuft of Funaria which was laid upside down 

 under a bell-glass for about two weeks, and occasionally damp- 

 ened. The protonema developed from the rhizoids has already 

 produced a large number of leafy shoots. A tuft of Mnium 

 similarly treated will produce a like result. This shows that 

 although the rhizoids differ from the protonema in their ten- 

 dency to grow downwards, and in not containing chlorophyll, 

 yet there is no sharp distinction between the two ; each possess- 

 ing the power of producing leaf stems which differ in no respect 



