LICHENE8. 



295 



study of the young aud forming knot, while the succeeding ones will 

 show first the conidia, and then the forming perithecia and developing 

 asci and ascospores. The last gathered specimens in February will 

 show the fully formed ascospores. 



(e) Ergot, which occurs on rye and many of the forage grasses, is 

 poisonous, producing gangrenous sores when eaten in considerable 

 quantities. It is used somewhat in medicine. 



(/) Xylomites in the Jurassic, and Sphceria, P/tacidium, Rhytisma 

 and other genera, in the 

 Eocene and Miocene, are 

 the fossil representatives 

 of this order. 



391 .Order Lich- 

 enes. Lichens agree, 

 in all the essentials of 

 their structure, with 

 the two preceding or- 

 ders, HelvellacecB and 

 Pyrenomycetes, and 

 there can no longer 

 be shown any good 

 reasons for not class- 

 ing them with the 

 latter, under the As- 

 corny cetes. 



392. The tissues 

 of lichens consist of 

 various aggregations 



Of Colorless, jointed Fig. SOI. Transverse 



, , , Sticta fuliginosa. r>, co 



nypnffl ; 111 general face ; u. cortical layer o 



, i i v , i or attaching fibres ; m, medullary layer, couioosed of 



the hypliae in the COr- distinct hyph;e, many of which are cut transversely ; 



rir-al -urn-firm rf tlio 0, layer ol green gonidia. Eachgonidia group is mir- 



tical poition O me rounded by a gelatinous envelope. X 550. -After 



thallus are compact- Sachs- 



ed and developed into a pseudo-parenchyma (o and u, Fig. 201, 

 and cc, B, Fig. 202), while in the medullary portion they are 

 distinct (m, Fig. 201, and cm, B, Fig. 202). In all lichens 

 there occur numerous green, blue-green, or brown-green cells, 

 the gonidia, which are either scattered through the interior 

 (homoomerous), or disposed in one or more distinct layers 

 (heteromerous) ; of the former, Collema and Le-ptogium are 



section of the thallus of 

 cortical layer of the upper sur- 

 layer of lower surface ; r, rhizoid^ 



