EMBRVOLOGV OF MOSS. 739 



c is situated. C represents a longitudinal section through the spore-capsule, which 

 consists of various layers of parenchymatous tissue within a very strong and well 

 developed epidermis, and forms anteriorly the lid (Operculum) d, already men- 

 tioned. A central mass of tissue {/) composed of large cells, is separated by 

 means of large intercellular spaces /i from the peripheral layers of tissue of the 

 cajisule, and is distinguished as the columella. A layer close to the periphery 

 of the columella produces the mother-cells, each of which gives rise to four spores 

 by repeated bipartition. It may here be remarked that the spores of the Vascular 

 Cryptogams, just like those of the Mosses, also arise from their mother-cells as 

 tetrads (quarters), and that the pollen-grains of the flowering plants do exactly the 

 same, since they also are in fact nothing other than spores. 



When the spores of the Moss-capsule are ripe, the operculmii ^/ (Fig. 420 C), 

 which consists of epidermis, becomes loosened from the urn-shaped portion of 

 the fruit at a, the large-celled parenchyma becoming disorganised, and thus the 

 cavity containing the spores opens. In the more 

 highly organised Mosses there remains, after the 

 falling away of the operculum, a simple or double 

 crown of beautifully formed organs, the Peristome, 

 composed of solid portions of the cell-walls of the 

 tissue which fills up the cavity of the operculum ; 

 this contributes to the dissemination of the spores, 

 the ' teeth ' of the peristome rolling up and unrolling 

 hygroscopically. Fig. 421 shows the structure of 

 a double peristome in a particularly excellent ex- 

 ample. 



The spores when emptied out of the capsule „.eSofli^^^^irL:;:)^ 



germinate and give rise to the protonema, from the {:'',", 'Some T .>' int^ai 



consideration of which we started above. peristome. 



I will describe the reproductive organs and 

 alternation of generations of the isosporous Vascular Cryptogams so far as is needful 

 for our purpose, in the case of the Ec|uisetace8e or Horse-tails, taking as an example 

 the largest and handsomest of our native species, Eqtiisetum Telmakia, with which 

 moreover the common Equisetmii arvense of the fields, abundant ever \- where in 

 pastures &c., agrees. All the species of Equisetum live chiefly under ground, where 

 their shoots, which have the form of rhizomes, grow on in part horizontally, in part down- 

 wards, and often occupy large areas. On the rhizome are produced buds which are 

 directed upwards from the first, and in the spring grow upwards, often from consider- 

 able depths, to expose themselves to the daylight ; these shoots, however, are of two 

 kinds. Some of them, which do not emerge until later, when the weather is warmer, 

 grow up to the height of a man and produce in the axils of their membranous leaf- 

 sheaths whorls of thin lateral shoots, which then again branch in like manner; these 

 are the foliage shoots of these plants, the tissue containing chlorophyll however being 

 developed not in the inconspicuous leaf-sheaths, but in the cortex of the secondary 

 and tertiary shoot-axes. Their products of assimilation pass into the subterranean 

 rhizomes, and these, under favourable conditions, may probabl}' go on living for 

 hundreds of }"cars. 



3 B ^ 



