130 Plant Biology 



multicellular spore-forming spore cases, called sporangia (spor -anj' i a) 

 (Gr. sporos, spore or "seed"; anggeion, vessel) are also protected by a 

 sterile jacket layer. These protective jacket layers are necessary in land 

 plants where they are subjected to a variety of environmental influences. 

 All embryophytes reproduce by oogamy (o -og' a my) (Gr. oon, ^g^; 

 gamos, marriage) in which unlike sex cells (gametes) fuse and the egg 

 cell is nonmotile. All have a definite alternation of generations in which 

 a multicellular sporophyte (spor' o fite) (Gr. sporos, spore; phyton, plant) 

 alternates with a multicellular gametophyte (gam e' to fite) (Gr. gametes, 

 spouse; phyta, plants) . '^ 



Embryophytes are essentially terrestrial (land plants), although a few 

 species may live in water. They all contain chlorophyll in green plastids. 

 The aerial parts of the plants may be protected by a layer of waxlike 

 cutin. Embryo phyta include the two phyla Bryo phyta and Tracheophyta, 

 both of which are considered in greater detail in later chapters. 



9. Phylum Bryophyta (bri -of i ta) (L. hryon, moss; phyta, plants) . — 

 The Bryophytes include the liverworts, which belong to the class Hepaticae 

 (he -pat' i se) (L. hepaticus, liver), and the true mosses, which belong to 

 the class Musci (mu' si) (L. muscus, moss). They are terrestrial plants 

 which require a certain amount of moisture for their living activities, and 

 water is required for the transmission of the male sperm to the female 

 egg. They possess chlorophyll in chloroplasts for the process of photo- 

 synthesis. Liverworts and true mosses possess similar methods of repro- 

 duction arid life cycles and are much alike structurally and functionally 

 in spite of differences which may appear upon casual observation. In 

 general, the plant body of Bryophytes is never filamentous but is com- 

 posed of blocks, or sheets, of cells forming a parenchymatous tissue 

 (par eng -kim' a tus) (Gr. para, beside; engchyma, infusion) composed of 

 cells with rather thin walls. Consequently, none of the Bryophytes grow 

 to any great height. 'They lack true roots, true stems, and true leaves, 

 because they lack the vascular tissues, xylem and phloem, which are 

 present in higher plants. Rootlike rhizoids anchor the plants and absorb 

 materials from the substratum. 



Bryophytes possess alternation of generations in which a multicellular 

 gametophyte alternates with a multicellular sporophyte. The latter is 

 more or less dependent upon the gametophyte. The multicellular, 

 gamete-producing gametangia (gam e -tan' ji a) (Gr. gametes, gametes, 

 or spouse; anggeion, vessel) possess a protective layer of sterile cells. 

 Bryophytes develop a multicellular embryo from the fertilized egg 

 (zygote), from which the sporophyte develops. No asexual spores are 



