SECTION 17. J 



BRYOrHYTES. 



105 



and very liygromrtrio threads (called Elafers) which are thought to aid in 

 the dispersion of the spores. (Fig. 542-544.) 



502. Marchautia, tlie commonest and largest of the true Liverworts, 

 forms large greeu plates or fronds on damp and shady ground, and sends up 

 from some part of the upper face a stout stalk, ending in a several-lobed 

 umbrella-shaped body, under the lobes of which hang several thin-walled 

 spore-cases, which burst open and discharge spores and elaters. Riccia 

 natans (Fig. 545) consists of wedge-shaped or heart-shaped fronds, which 

 float free in pools of still water. The under face bears copious rootlets ; iu 

 the substance of the upper face are the spore-cases, their pointed tips 



merely projecting : there they burst open, and discharge their spores. 

 These are compai-atively few and large, and are in fours ; so they arc very 

 like the macrospores of Pillworts or Quillworts. 



503. Thallophyta, or Thallophytes in English form. This is the name 

 for the lower class of Cellular Cryptogams, — plants iu which there is no 

 marked distinction into root, stem, and leaves. Roots in any proper sense 

 they never have, as organs for absorbing, although some of the larger 

 Seaweeds (such as the Sea Colander, Fig. 553) have them as holdfasts. 

 Instead of axis and foliage, there is a stratum of frond, in such plants 

 commonly called a Thallus (by a strained use of a Greek and Latin word 

 which means a green shoot or bough), whicli may have any kind of form, 

 leaf-like, stem-like, branchy, extended to a flat plate, or gathered into a 

 sphere, or drawn out into threads, or reduced to a single row of cells, or 

 even reduced to single cells. Indeed, Thallophytes are so multifarious, so 

 numerous in kinds, so protean in their stages and transformations, so re- 

 condite in their fructification, and many so microscopic in size, either of 



Fig. 542. Fructification of a Jungermannia, magnified; its cellular spore-stalk, 

 surrounded at base by some of the leaves, at summit the -i-valved spore-case open- 

 ing, discharging spores and elaters. 543. Two elaters and some spores from the 

 same, higlily magnified. 



Fig. 544. On'3 of the frondose Liverworts, Steetzia, otherwise like a Junger- 

 mannia ; the spore-case not yet protruded troin its sheath. 



