144 PRACTICAL BOTANY. 



balsam or glycerine, are best for this observation. 1 Sec- 

 tions cut from fresh material and mounted in water or 

 glycerine will do. On the upper portion of the apothe- 

 cium, just below the epidermis, find ovoidal cells, the 



asci, arranged perpen- 

 dicularly to the surface, 

 large end outward ; each 

 ascus, or sac, contains a 

 number of spores. Be- 

 tween the asci are long 

 narrow cells, also ar- 

 ranged perpendicularly 



FIG. 83. -A vertical section through the to the surface; these are 

 gelatinous Lichen, Leptogium scotinum, 

 howing the algal constituents scat- paraphyses. The asci 



and Paraphyses together 

 make up the hymenium. 

 (Compare Figs. 77 and 81.) Just below the hymenium 

 is the subhymenial layer, composed of dense, interlacing 

 fungal elements. Below this is the layer bearing the 

 algal constituents, which extend entirely around the sec- 

 tion. Inside the algal layer the fungal constituent be- 

 comes looser for a space, but in the central portions again 

 becomes dense. 



Treat a section passing through the apothecium, made 

 from fresh material and mounted in water, with very 

 dilute iodine solution. The tissues of the hymenium 

 take on a blue color the starch reaction. Treatment 

 with Schultze's solution gives a similar result. The cell 

 walls of the hymenial tissues are composed of modified 

 cellulose, known as starch cellulose. Do iodine solution 

 and Schultze's solution give the blue color in other 

 portions of the fungal constituents ? In the algal con- 



1 For the processes used in the preparation of vegetable specimens for 

 sectioning and mounting consult the author's "Practical Methods in 

 Microscopy," Chap. VII. 



