TYPES OF CRYPTOGAMS; THALLOPHYTES 



271 



329. The Fruit. Look for small lance-shaped disks seated upon 

 the thallus. Note the approximate sizes and color within and 

 without. These disks are called apothecia. Note the very minute 

 black specks (spermogones) which are scattered in the surface of 

 the thallus. Pick one from the thallus, with as little of the thallus 

 as possible, and examine under high power. It may be macerated 

 in a drop of potash solution and crushed under the cover-glass. If 

 the contents are not easily 

 denned, they may then be 

 made more opaque by a drop 

 of acetic acid or a stain. The 

 minute colorless bodies con- 

 tained in the spermogones are 



FIG. 198. A Lichen (Xanthoria). 

 (Natural size.) 



FIG. 199. A Lichen (Usnea). 

 (Natural size.) 



called spermatia. Their office in Physcia is obscure, but in a few 

 lichens they are thought to unite with a trichogyne cell, as in the red 

 algae. 1 Note the minute, powdery masses (soredia) on the surface 

 of the thallus. Macerate if necessary under the cover-glass and 

 examine under a high power. Compare with the structure of the 

 thallus as seen in cross-section. (See next paragraph.) These soredia 

 easily become detached and develop into new plants. 



Prepare for sectioning by imbedding a small portion of the 

 thallus with an apothecium in a piece of pith or by any suitable 

 device for sectioning, and cut thin sections of thallus and fruit. 



1 This, however, is doubtful. See Strasburger, Noll, Schenk, and 

 Schimper's Text-Book of Botany, p. 380. 



