LI0HENE8. 



295 



study of the youncf and forming knot, while the succeeding ones will 

 bIiow 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, pioducing gangrenous sores when eaten in considerable 

 quantities. It is used somewhat in medicine. 



(/) Xy^omites in the Jurassic, and Sphmria, Phacidium, Shytiama 

 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, Helvellacem and 

 Pyrenom.ycetes, 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 

 Tarious aggregations 

 of colorless, jointed 

 hyphse ; in 



Fig. 201.— Transverse section of the thallns of 



, SUcta /uliginosa. o, cortical layer of tlie upper snr- 



general face ; u, cortical layer of lower surface ; r, rhizoid.i 



,,,,.,-, or attaching fibres ; m, medullary layer, composed of 



the hypnae in tne cor- distlncthyphie, many«f which ai-e cut transversely; 



,. 1 /• » .1 (7, layer of green gonidia. Each gonidia group is snr- 



ticai portion OI tno rounded hy a gelatinous envelope. X 650.— After 



thallus are compact- ^*'''"" 



ed and developed into a pseudo-parenchyma (o and u, Pig. 301, 

 and cc, B, Pig. 302), while in the medullary portion they are 

 distinct (m, Pig. 201, and cm, B, Pig. 303). 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 

 Qieteromerous) ; of the former, Collema and Leptogium are 



