SECTION 17. J BRYOPHYTES. 1G5 



aud very hygromctric threads (called Elatcrs) which arc tliought to aid in 

 the dispersion of the spores, (i^'ig- 5i2-5-ii.) 



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

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

 from some part of the upper face a stout stalic, ending in a several-iohcci 

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

 spore-eases, which burst open and discharge spores and claters. 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 ; in 

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



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

 These are comparatively few and large, and are in fours ; so they are very 

 like the maerospores of Pillworts or Quillworts. 



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

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

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

 they never have, as organs for absorbing, althougli 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 Tiiallus (by a strained use of a Greek and Latin w-ord 

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

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

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

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

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

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



Fig. 5i2. Fructification of a Jungernianiiia, magnified; its cellular spore-stalk, 

 surrounded at base by .-^ome of the leaves, at suiiiniit the 4-valved spore-case open- 

 ing, discharging spores and elatcrs. 543. Two elaters and some sjiores from tho 

 same, highly magnified. 



FiQ. 544. One of the frondose Liverworts, Steetzia, otherwise like a Junker 

 mannia; the spore-case not yet protruded from its slieath. 



