198 GUIDE TO THE STUDY OF LICHENS. 



Considerable variation has been noted in the apo- 

 thecial characters of some Stictas which leads to the 

 conclusion that some of the apothecia may be the fruc- 

 tification of a fungal parasite closely related to Arthonia. 

 Particularly has this been observed in S. pulmonaria. 

 Further careful research is necessary to determine the 

 parasites living upon lichens. Let us hope that some 

 of the amateurs for whom this book is written may 

 make observations and studies which will aid in clear- 

 ing up some of these mysteries. 



The Stictas are less distinctively southern in their 

 range. The change in algal symbiont may have en- 

 abled the plants to thrive in a colder climate. They 

 occur upon rocks and trees. 



1. Sticta amplissima. Thallus large, parmelioid, 

 rather thin and papery, lobed, grayish-green and 

 smooth above ; brown beneath, with rhizoids but no 

 cyphellae. Apothecia rather large, numerous. Disk 

 chestnut-brown. Spores colorless, long, slender, some- 

 what curved, indistinctly septate, 46/x X 6/x. 



2. Sticta pulmonaria. Thallus large, lobes long, 

 upper surface divided into concave areas, ridges and 

 margin lined with soralia, dirty brown tinged with 

 bluish-green ; lower surface of convex areas light- 

 brown, no cyphellae. Apothecia few, medium. Disk 

 reddish-brown to dark. Spores very closely resemble 

 those of Arthonia, 18/x X 5.5/x. 



This lichen quite generally occurs at the base ot 

 trees (weather-side) at high altitudes. It is usually 

 isolated, and the entire plant has the appearance of 

 being decrepit and old, so that upon seeing it for the 



