342 THE MICROSCOPE AND ITS REVELATIONS. 



ject for the Binocular Microscope; it is very ' hygometric,' executing, 

 when breathed-on, a curious movement, which is probably concerned in 

 the dispersion of the spores. In Figs. 222-224, are shown three different 

 forms of peristome, spread out and detached, illustrating the varieties 

 which it exhibits in different genera of Moses; varieties whose existence 

 and readiness of recognition render them characters of extreme value to 

 the systematic Botanist, whilst they furnish objects of great interest and 

 beauty for the Microscopist. The peristome seems always to be originally 

 double, one layer springing from the outer, and the other from the inner, 

 of two layers of cells which may be always distinguished in the immature 

 capsule (Fig. 219, c, p); but one or other of these is frequently wanting 

 at the time of maturity, and sometimes both are obliterated, so that there 

 is no peristome at all. The number of the ( teeth ' is always a multiple 

 of 4, varying from 4 to 64: sometimes they are prolonged into straight or 

 twisted hairs. The spores, or gonidial cells, are contained in the upper 

 part of the capsule, where they are clustered round a central pillar, which 

 is termed the columella. In the young capsule the whole mass is nearly 

 solid (Fig. 219, c), the space (I) in which the spores are developed being 

 very small; but this gradually augments, the walls becoming more con- 

 densed; and at the time of maturity the interior of the capsule is almost 

 entirely occupied by the spores. These are formed in groups of four, by 

 the duplicative subdivision of the ' mother-cell * which first differentiate 

 themselves from those forming the capsule itself. Thus the ' spore-cap- 

 sule in Liverworts and Mosses, being the immediate product of the act of 

 fertilization (which constitutes the point of departure of each 'new gene- 

 ration'), is to be considered as the progeny of the plant that bears it; 

 which, supplying the nutriment at whose expense it develops itself, acts 

 as its 'nurse.' 



338. The development of the spore into a new plant commences with 

 the rupture of its firm, yellowish-brown outer-coat, and the protrusion of 

 its green cell-wall proper; from the projecting extremity of which new 

 cells are put forth by a process of out-growth, which form a sort of Con- 

 fervoid filament (as in Fig. 231, c). At certain points of this filament, 

 its component cells multiply by subdivision, so as to form rounded clus- 

 ters, from every one of which an independent plant may arise; so that 

 several individuals may be evolved from a single spore. And as a 

 numerous aggregate of spores is developed, as we have seen, from a sin- 

 gle germ-cell, the rapid extension of the Mosses is thus secured, although 

 no separate individual ever attains more than a very limited size. 



339. The tribe of Sphagnacece or ( Bog-Mosses,' is now separated by 

 Muscologists from true Mosses, on account of the marked differences by 

 which they are distinguished; the three groups, Hepaticce, Bryacece (or 

 ordinary Mosses), and Sphagnacea, being ranked as together forming the 

 Muscal Alliance. The stem of the SpliagnacecB is more distinctly differ- 

 entiated than that of the Bryacece into the central or medullary, the outer 

 or cortical, and the intermediate or woody portions; and a very rapid 

 passage of fluid takes place through its elongated cells, especially in the 

 medullary and cortical layers, so that if one of the plants be placed dry 

 in a flask of water, with, its capitulum of leaves bent downwards, the 

 water will speadily drop from this until the flask is emptied. The leaf- 

 cells of the Sphagnacece exhibit a very curious departure from the ordi- 

 nary type: for instead of being small and polygonal, they are large and 

 elongated (Fig. 225); they contain no chlorophyll, but have spiral fibres 

 loosely coiled in their interior; and their membranous walls have large 



