LIVERWORTS AND MOSSES. Si 



phyte perishes at the close of the growing season, but more 

 commonly it is perennial, growing and branching at the 

 anterior end as the older posterior parts die away. 



62. Summary. — Liverworts and mosses show a distinct 

 alternation of generations. The vegetative body of the sim- 

 pler liverworts is a flat thallus, like that of the larger algae, 

 but the higher forms have the central part developed as a 

 roundish stem, and the wings so branched as to form separate 

 leaves. The latter form is general in all the mosses, which 

 further have the stem and often the leaves stiffened by the 

 differentiation of mechanical tissues. The non-sexual genera- 

 tion in all is relatively small and depends for its food upon 

 the sexual generation. 



EXERCISE XIII. 



A moss {Mnium cuspidatum). — Examine plants with capsules attached. 

 Observe the two connected plants : 



1. The leafy stemmed plant or ^o»«^i'i7//4j/<f. (1[ 50.) 



2. The slender plant attached to its tip, the sforophyte, consisting of 

 a wire-like stalk, the seta, enlarged above to form the hanging capsule. 

 (H 60, fig. 46.) 



3. Boil for a few minutes in 5 per cent, potassic hydrate, rinse in 

 water and gently pull sporophyte until it separates from the gametophyte. 

 Observe the smooth pointed end which was sunk in gametophyte. If 

 properly separated no sign of tearing can be seen. (Fig. 47. ) 



Examine gametophyte in water. Observe 



4. The differentiation of the body into stem and leaves. 



5. The brown hairs [rhizoids) about the stem, which attach plant to 

 ground. Do they branch ? (1[ 55.) 



6. The strength of the stem ; test it by breaking it with a lengthwise 

 pull. Cut a thin transverse section and observe dark colored mechanical 

 tissues in outer region. (If 56. ) 



7. The form and structure of the foliage leaves : note midrib of me- 

 chanical cells (test strength) ; lamina of one layer of cells large enough 

 to be visible under lens ; border of mechanical cells, some projecting 

 pretty regularly as teeth. (^ 57, fig. 43.) 



8. Smaller, scale-like leaves on part of the stem. 



