SECTION 17. J 



BRYOPHYTBS. 



165 



and very hygrometric threads (culled Elaters) which arc thought to aid in 

 the dispersion of the spores. (Fig 5 I I 5 II) 



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

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

 from s«»me part of the upper face a si out 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 

 nutans (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 arc the spore-cases, their pointed tips 



542 



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

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

 like the macrospores of Pill worts 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, 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 Tiiallus (by a strained use of a Greek and Latin word 

 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 

 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 



Fio. 642. Fructification of a Jungermannia, magnified; its cellular Bpore-ttalk, 

 Burronnded at base by some of the leaves, at summit the L-valved spore-case open- 

 in.', discharging spores and slaters. 648. Two elaters and some spores From the 

 same, highly magnified. 



Fig. 544, One of the frondose Liverworts! Steetda, otherwise like a Junger 

 uiaimia; the spore-case not yet protruded from its sheath. 



