40 OUTLINES OF PLANT LIFE. 



Cut a vertical section through a part of the thallus. Observe 

 5. The layers of the thallus ; above and below, dense layers^ the 

 upper and lower cortical layers ; between them, the medullary layer, 

 with green alga, distributed unequally through it. (Fig. 36. ) 



49. Summary. — The fungi, though descended from the 

 algae, have adapted their body to new conditions of life so 

 completely that it shows little resemblance to that of the algse. 

 All have colorless (non-green) bodies, composed of slender 

 hyphse, frequently much branched and interwoven, and either 

 applied to the surface or penetrating the substratum. Some 

 kinds live on dead organic matter (saprophytes); some are 

 external and some internal parasites. The latter enter the 

 host' through pores, or by perforating the skin, often causing 

 deformity or disease or death. When strength or protection 

 or durability is necessary, the hyphae may become insepara- 

 bly fused into a false tissue. Lichens are special kinds of 

 fungi, associated for life with simple algse from which they 

 derive their food. 



