CHAPTER IV 



saucer-shaped, and have a smooth, almost polished inner surface, often 

 of contrasting color. The nature of the fungus part is made more or 

 less apparent by loosening the lichen from its substratum, or by pick- 

 ing it apart. If lichens in any considerable quantity can be obtained, 

 their avidity for water can be shown by measure or weight. Some 

 lichens absorb fifty per cent of their weight of moisture in ten minutes. 

 Water often dissolves the pigment of the lichens, and usually it 

 renders the green color of the layer of algae just beneath the upper 

 surface more apparent. 



The remarkable symbiosis between the two kinds of plants, the 

 fungus and the algae, which make up the lichen, has been discovered 

 only in the latter half of our own century, but it seems now to be 

 generally accepted as a fact. Full demonstration of it could not, of 

 course, be undertaken in an ordinary school-room, but the inter- 

 weaving hyphae of the fungus and the imbedded algae (or more 

 properly green plants of even lower rank) can be shown under a 

 moderately high power of the microscope. More skillful manipula- 

 tion is necessary to show the spore-sacs clearly. Any one attempting 

 this for the first time would better begin with the spore-fruits of the 

 " cup fungus," or Peziza, which is nearly related to the lichen fungus, 

 and is neither tough nor brittle. The spore-fruits of the Peziza are 

 rather common in manure during the rainy season ; the most common 

 kind is a light brown or amber cup, from one and a half to two 

 inches in diameter ; the inner surface of the cup is velvety, and a 

 vertical section shows that every thread of the pile of the velvet is a 

 slender, delicate sac, many sacs containing eight spores. If you keep 

 these spores under observation, you will see that on maturity they 

 suddenly expel little clouds of spores. The sacs that form the lining 

 of the lichen cups are much smaller and have their tips hardened, that 

 is, it is their hardened tips that form the polished inner surface of 

 the cup. They, too, expel their spores at maturity, and bodies so 

 minute and in such multitudes are sure to be scattered everywhere by 

 the winds. The*se spores, of course, belong to the fungus part of the 

 lichen, but myriads of the one-celled host plants in their resting stage 

 are also blown about. A piece of moist blotting paper exposed to the 

 wind, even on a high mountain top, will collect a goodly number of 

 both fungus spores and host plants. The coarser, meal-like powder 

 often seen on lichens, consists of fragments, little colonies of algae 

 and fungus combined, that are capable of growing into independ- 

 ent lichen bodies. 



It is hoped that the subject of nutrition is made clear in the Reader. 

 The green host plants act as green cells always do in making 



