164 



KNOWLEDGE 



[July 1, 1898. 



condition, the addition of a drop of water, or slight 

 pressure of the cover-glass, will cause part of the con- 

 tents to escape by an aperture formed at the apex. The 

 antheroioids, or spermatozoich, may then be seen coiled 

 up, each in a thin membrane, which soon bursts and 

 sets it free. 



The female plants are, as has already been noticed, less 

 conspicuous. Tue top of the stem is not expanded to form 

 a "capitulum," and the surroundmg leaves are but slightly, 

 if at all, modified. A section through the end of such 

 a shoot will show numerous archegonia surrounded by 

 paraphyses, which in this cise have the form of long 

 jointed hairs, without the inflated terminal cells seen 

 in those of the male flower. The archegonia are long 

 and slender; the "venter" or chamber containing the 

 egg-cell is of an oval shape, narrowing below into a 

 cellular stalk of considerable length. The elongated neck 

 consists of the typical four rows of outer cells surrounding 

 the channel filled with mucilage through which the sperma- 

 tozoids reach the oo3phere. 



When fertilization has been effected there is an 

 immediate increase in size of the oospore, followed by 

 division into several cells, forming the commencement of 

 the sporophyte. The latter soon comes to consist of a 

 cylindrical mass of cells, growing down for some distance 

 into the tissues of the parent stem, but growing more 

 rapidly upward. This physiological activity is not, 

 however, confined to the sporophyte proper. The walls of 

 the archegonium and the tissues round its base are also 

 wakened into fresh activity, and for a time keep pace 

 with the increase of the new generation. For a consider- 

 able time the developing sporophyte is thus surrounded by 

 a tissue of cells representing the original wall and part of 

 the neck of the archegonium, with others due to an increase 

 of the tissues round its base. In time, however, the up- 

 growth of the sporophyte is too rapid for its surrounding 

 wall ; the latter is torn across transversely, leaving a 

 basal portion as a sheath or " vaginula " round the base 

 of the new plant, while the rest is carried upward as a 

 cap or "calyptra" covering the tip. 



The sporophyte grows on as a long slender rod, often 

 till it equals in length the stem of the parent plant before 

 there is any marked appearance of the capsule at its apex. 

 In time the thickening of the terminal portion of the 

 sporophyte indicates the development of the sporangium, 

 and in this instance the successive stages are accompanied 

 by gradual change of position ; the original vertical apex 

 becomes oblique, then horizontal, and finally pendent. 

 Daring these changes the little cap or calyptra is dropped 

 or carried away by the wind. It is only slight in this 

 genus, but is seen at its best in the silky bells of 

 Polytrichum and the long "extinguisher" of Eucalt/jita. 

 When it has fallen the end of the capsule will be seen 

 to be closed by a distinct circular lid, the operculum 

 sharply separated by an annular ridge from the capsule 

 wall. 



The capsule changes from green to yellow and then to 

 brown as the spores within it are ripening. In time the 

 operculum is thrown off, and with its removal may come a 

 burst of gold dust as the spores scatter to the winds. 

 I say "may come" because, though the fall of the 

 operculum probably coincides in nature with favourable 

 conditions, yet nature has provided a second safeguard 

 against premature dispersal of the spores. This is the 

 peristome, one of the most remarkable and beautiful 

 structures in the cryptogamic world. Originating as a 

 series of thickenings on the walls of the cells internal to 

 the annulus, and stretching over the end of the columella, 

 the struoture finally takes the form of a membrane divided 



radially into a number of wedge-shaped teeth. In some 

 cases only one layer of cells is thus modified — one set of 

 " teeth " produced^and the peristome is then said to 

 be " simple." In others, such as the type we are 

 considering, there is an inner and an outer layer, so that 

 the peristome is double. The outer peristome consists of 

 sixteen triangular teeth, marked by transverse thickening 

 bars. In the dry state their tips meet at the centre, and 

 close the opening of the capsule ; when moist they separate 

 and curve upward or backward. The inner peristome is a 

 continuous membrane in its outer half, but toward the 

 centre is radially divided into sixteen forked teeth opposite 

 those of the outer circle, and sixteen pairs of jointed 

 hairlike threads alternating with them. These inner 

 structures are also " hygroscopic," or sensitive to changes 

 in the moisture of the air ; and their consequent expansion 

 or contraction causes the escape or retention of the spores, 

 according to atmospheric changes. 



If a fair-sized capsule which has not yet begun to turn 

 dry and brown is selected, it wUl ba found possible, 

 though not without some trouble, to cut a thin longitu- 

 dinal section through the middle, and examine it under 

 the microscope. 



Fig. B in the illustration is a somewhat diagrammatic 

 representation of the more important features to be 

 observed. There is an outer rpiitmnal cell-layer and two 

 or three rows of cells internal to it, forming the capsule 

 uall : a solid cylindrical tissue of cells, the columella, 

 occupies the centre, and is separated from the wall by an 

 <iir space crossed by irregular strings of cells. The outer 

 layers of the columella, the inner layer of the wall, and 

 the threads crossing the air space are all green, from the 

 presence of chlorophyll granules in them. Internal to 

 the outer green cells of the columella is a specialized 

 layer which will vary in appearance according to the stage 

 of development of the specimen examined. This is the 

 archesporium, or layer from which the spores are developed. 

 In an early stage it appears in section as a single row of 

 large, square, dark, and granular-looking cells with large 

 round nuclei. At a later stage the cells will be found in 

 a condition of active multiplication, dividing into two and 

 four by walls at right angles to each other. The new 

 cells thus formed are termed the spore mother-cells .- they 

 subsequently become free within the capsule, lying in a 

 semifluid material formed by the degeneration of sur- 

 rounding cells and their cell walls. In this position they 

 divide again, and the resulting cells assume a spherical 

 shape, develop an outer covering of two layers (endospore 

 and exospore), and ripen into spores. As they ripen the 

 other contents of the capsule dry up and disappear ; a drop 

 of water on the ripe capsule causes the cells of the annulus 

 to swell, the operculum is thrown off, the peristome 

 teeth rise up, and separating from one another give the 

 spores free exit to the air. Spores falling on favourable 

 spots commence to germinate, and we thus return to the 

 stage in the life history with which we started. 



The result, then, of our study of the moss plant may be 

 summarized somewhat as follows :• — (1) The general struc- 

 ture and life history of a moss is similar to that of a 

 leafy Hepatic like Junnermannia : but (2) there is far 

 greater specialization in detail than in any members of 

 the latter group, both in the oophyte and sporophyte 

 generations. In the sporophyte the chief differences are : 

 ((() that only part of the cells of the capsule — a special layer 

 or archesporium — develop into spores ; {h) that no elaters are 

 formed ; {c) that the sporophyte grows up, protected by 

 the calyptra, before the development of the capsule ; {d) that 

 the capsule wall does not split into four segments, but 

 remains entire, the spores escaping by a terminal opening 



