THE MICROSCOPE IN HISTOLOGY AND BOTANY. 155 



The Sphagnum, or bog-moss, has large and elongated 

 leaf-cells, with loosely-coiled spiral fibres, and their mem- 

 branous walls have large apertures. Their spores are of 

 two kinds, and when germinating in water, produce a long 

 filament with root-fibres at the lower end and a nodule 

 at the upper, from which the young plant is formed. If 

 grown on wet peat, instead of a filament there is evolved 

 a lobed foliaceous prothallium, resembling the frond of 

 liverworts. 



In ferns the structure approximates to true flowering 

 plants, while the reproductive organs are those of crypto- 

 gamia. Thin sections of the stem, cut obliquely, show 

 the scalariform or ladder-like vessels. The fructification 

 is usually found on the under side of the frond in isolated 

 spots called son. Each of these contains a number of cap- 

 sules or thecce, and each capsule is surrounded by an an- 

 nidus or ring, whose elasticity opens the capsule when 

 ripe and permits the spores to escape. The spores are 

 somewhat angular, and when vegetating give rise to a 

 leaf-like expansion called a prothallium. In this the an- 

 theridia and archegonia, which represent the true flower 

 of higher plants, are developed. The ciliated anthero- 

 zoids from the antheridia penetrate the cavity of the 

 archegonium and fertilize the " germ-cell," which subdi- 

 vides and becomes a young fern, while the prothallium, 

 having discharged the functions of a nurse, withers away 

 (Plate XI, Fig. 114). The group of EquisetacecR or horse- 

 tails is interesting from the siliceous skeletons of the epi- 

 dermis, already referred to, page 131, as well as for the 

 elastic filaments attached to their spores. 



EXAMINATION OF HIGHER PLANTS. 



The elementary tissues described in the beginning of 

 this chapter are chiefly characteristic of phanerogamic 

 plants, yet some additional particulars remain to be no- 



