74 



BOTANY. 



Ji 



are at first almost closed, but expand as they mature (Fig. 44, 

 A, ap.). 



If a thin vertical section of the plant is made and sufficiently magnified, 

 it is found to be made up of somewhat irregular, thick- walled, colorless 

 filaments, divided by cross- walls as in the other sac-fungi. In the central 

 parts of the plant these are rather loose, but toward the outside become 

 very closely interwoven and often grown together, so as to form a tough 



rind. Among the filaments 

 of the outer portion are nu- 

 merous small green cells, 

 that closer examination 

 shows to be individuals of 

 Protococcus, or some simi- 

 lar green algee, upon which 

 the lichen is parasitic. 

 These are sufficiently abun- 

 dant to form a green line 

 just inside the rind if the 

 section is examined with a 

 simple lens (Fig. 44, B). 



The spore fruits of the 

 lichens resemble in all es- 

 sential respects those of 

 the cup fungi, and the spore 

 sacs (Fig. 44, F) are much 

 the same, usually, though 

 not always, containing eight 

 spores, which are some- 

 times two-celled. The ster- 

 ile filaments between the 

 spore sacs usually have 



D, a spermagonium of "Collema, x 25. E, a thickened ends, which are 

 single Nostoc thread. F, spore sacs andpara- 

 physes of Usnea, x 300. G, Protococcus cells 

 and fungus filaments of Usnea. 



FIG. 44. A, a common lichen (Parmelia), of 

 the natural size. ap. spore fruit. B, section 

 through one of the spore fruits, x 5. C, sec- 

 tion through the body of a gelatinous lichen 

 (Collema), showing the Nostoc individuals 

 surrounded by the fungus filaments, x 300. 



dark-colored, and give the 

 color to the inner surface 

 of the spore fruit. 



In Figure 45, H, is shown one of the so-called " Soredia," l a group of 

 the algae, upon which the lichen is parasitic, surrounded by some of the 



Sing, soredium. 



