LICHEXE8. 



295 



study of the young and 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, Phacidium, Rhytiama, 

 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, Hdvellacem and 

 Pyrenomycetes, and 

 there can no longer 

 be shown any good 

 reasons for not class- 

 ing them with the 

 latter, under the As- 

 comycetes. 



392. The tissues 

 of lichens consist of 

 various aggregations 

 of colorless, jointed 



in general face; u. cortical layer of lower surface^ r,*rb.Tzoida 

 ** in thp cnr ^ attaching fibres ; m, medullary layer, composed of 



tical portion of the 

 thallus are compact- Sachs< 

 eel 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 Leptogium are 



Fig. 201. Transverse section of the thallus of 

 Stlcta fuliffinpm. o, cortical layer of the upper sur- 



distincthyphte, many of which are cut transversely; 

 ff, layer of green gonidia. Each gonidia group is sur- 

 rounded by a gelatinous envelope. X 550. After 



