248 NUTRITIVE METABOLISM 



the epidermal cells resembling root hairs. The fungus will be 

 found to penetrate deeply into the cortex, forming dense clumps 

 in the interior cells, and looser coils in the outer layers. The 

 hyphae in the outer layers may be regarded as the mycelium of 

 the fungus which grows forward as the branch extends, sending 

 internal branches into the cortex and external branches- out 

 through the trichomes into the humus. Material absorbed by 

 the external hyphae is brought into the mycelium and its internal 

 branches, undergoing more or less synthetic change, and some it 

 diffuses into the protoplasm of the higher plant. Ascertain what 

 material in the cells of the Corallorhiza is taken up by the fun- 

 gus, and the probable nature of the material obtained by Corallo- 

 rhiza (Fig. 124). 1 



315. Arrangement of Components of Lichens. Examine the 

 structure of a Cladonia or Sticta and ascertain the structural 

 relations of the fungus and alga associated. 2 



316. Relations of a Fungous Parasite to its Host. Secure 

 plants of Bursa Bursa-pastoris (L.) Britton (CapsellaBursa-pastoris) 

 showing the whitish pustules due to Albugo Candida on the stems, 

 leaves, flowers and seeds. Cut sections of the material and stain 

 in a solution of potassium iodide and iodine. Note the relations 

 of the parasite and its host. Find the special absorbing organs, 

 the haustoria of the parasite. Some of the facts may be brought 

 to light more easily, if a fragment of the infested material is boiled 

 for a minute in a solution of potassium hydrate, washed with dis- 

 tilled water, then stained with the iodine solution. 



The structural arrangement of a parasite may also be seen by 

 an examination of the aecidium which is parasitic on Peltandra or 

 Arisaema showing yellowish pustules on the surfaces of the 

 leaves. 



1 MacDougal. The significance of mycorhizas. Biological lectures, Woods Holl 

 Marine Laboratory, p. 49. 1899. 



Stahl, E. Der Sinn der Mycorhizenbildung. Jahrb. Wiss. Bot. 34 : 539. 1900. 



Magnus, W. Studien an der endotrophen Mycorrhiza von Neottia Nidus avis L. 

 Jahrb. Wiss. Bot. 35 : Hft. 2. 1900. Sarauw, G. F. L. Rodsymbiose og Mykor- 

 rhizer saerlig hos Skovtrceerne. Bot. Tiddsskrift. 18: 127. 1893. 



2 Schneider, A. Text-book of general lichenology. 1897. 



