INTRODUCTION. 



345 



jpore-capsule, in the spiral bands of the elaters of Hepaticae, and in the formation 

 )f the epidermis and peristome of the thecae of Mosses. 



Classification of MuscineoB. The sexual generation is developed from the spore, 

 generally after the previous formation of a protonema. It is the longest-lived of the 

 two generations, and constitutes the self-supporting vegetative body of these plants, 

 presenting either a flat dichotomously branched thallus, or a thalloid stem, or a filiform 

 stalk furnished with from two to four rows of leaves. True fibro-vascular bundles 

 are not developed. The archegonia and antheridia are, except in the simplest thalloid 

 forms, stalked multicellular bodies, usually free, but sometimes buried in neighbouring 

 masses of tissue from the subsequent growth of these latter. The central cell of the 

 ventral part of the archegonium undergoes division, a ventral canal-cell being cut off, 

 and the remainder of its protoplasm constitutes the oosphere by rejuvenescence. The 

 antherozoids are spirally coiled threads with two cilia on the anterior pointed end. 



The asexual generation or sporogonium arises from the fertilised oosphere within the 

 actively growing ventral part of the archegonium, which becomes developed into the 

 calyptra. The sporogonium is nourished by the sexual plant; it has therefore no 

 independent existence, and appears externally as an appendage to it. It is usually a 

 stalked capsule, in which usually a number of cells are developed into the mother- 

 cells of the spores ; and from these the spores are formed by division into four after 

 bipartition has commenced but has not been completed. 



(i) Hepaticce. The sexual generation arises either directly from the spore or with 

 the intervention of a small inconsiderable protonema. It is developed as a flat dicho- 

 tomously branched thallus or a thalloid stem, or finally as a filiform stalk furnished with 

 two or three rows of leaves. This vegetative body is usually broadly expanded and 

 clings closely to the ground or to some other substratum ; even when the stems grow 

 erect there is still an evident tendency towards the distinction of an upper (dorsal) and 

 an under (ventral) surface. The mode of growth is hence^ always distinctly bilateral. 

 The asexual generation or sporogonium remains surrounded by the calyptra until the 

 spores are ripe ; the calyptra is usually at length ruptured at the apex, and remains at 

 the base of the sporogonium as an open sheath, while the free spore-capsule projects 

 above its apex, to allow the escape of the spores. The mother-cells of the spores arise 

 either from the whole of the cells except those of the single layer which forms the wall 

 of the capsule, or the intermediate cells commonly become developed into elaters: a 

 columella is present only in the Anthoceroteae. 



(2) Musci. The sexual generation is developed from the spore with the intervention 

 of a protonema consisting of branched rows of cells and often vegetating for a con- 

 siderable time independently, even when it has already produced leafy stems by lateral 

 budding. The vegetative body is here always a cormophyte, a filiform stem furnished 

 with leaves in two, three, or four rows, usually without any definitely indicated bilateral 

 structure, and generally branched in a monopodial, never in a dichotomous manner. 

 The asexual generation or sporogonium is only at first formed in the calyptra ; after- 

 wards this is usually ruptured below (at the vaginula), and raised up by the apex of 

 the sporogonium, which it covers like a cap. The capsule, which is now first developed, 

 produces the spores from an inner layer of tissue, while a large central mass of tissue 

 remains sterile and forms the columella. The wall of the capsule is covered by a 

 distinctly differentiated epidermis, the upper part of which usually becomes detached 

 from the lower part (the Urn) in the form of a lid, in order to allow of the escape of 

 the spores. 



