294 



color of the stroin.-i. I'nt this is not entirely satisfactory, because these 

 characters are not at all constant in a ,!?reat many species. Specimens of 

 a certain species may lie lonnd at one time which show the effused form 

 in a very marlaMl det^ree. Aj^ain specimeus of the same species may grow 

 in a iclohost' or hemispherical tnrni with scarcely a sign of the effused 

 nature. Similarly the color of the same species may vary greatly under 

 different conditions of growth and with increasing age. 



In any given si)ecies perhaps the sikuv measurements are the most 

 coustant of any of the characters, and even these vary within certain 

 limits. But the differences between the spore measurements of all the 

 various species are not of wide enough range to be of any great advantage 

 in throwing them into groups which would be usable in a key. It is true 

 that there are a few species here and there which might be thrown out 

 upon the basis of spore size, but the great majority of them range so 

 nearly together that it is not feasible to attem])t a key upon this basis. 



Since it lias been our final purpose to make a key which could be 

 used chiefly in the field without the use of the microscope, we have deemed 

 i1; be.st to follow, for the most part, the example of former writers. There- 

 fore the more evident, although more superficial and unstable characters 

 have been employed, and the key has been based to a large extent upon 

 the form and external color of the stroma. Although in a lew of the ulti- 

 mate divisions spore measurements have been used, it is hoped that in 

 most cases the student will l>e able to locate any of the species covered 

 by this key, by means of the naked eye, aided, perhaps, only by the hand 

 lens. 



ri'riiaiis not the least valuable aid in idcntilyiiig species may he found 

 ill the accompanying ligures. "When working with (phjccts whi<h art' of 

 such a uniformly dai'k appearance and which show such little contrast 

 between stroma and substratum as do nuist of the Hyjioxylons. it is no 

 easy task \i> jprodiicc (ihotographs which show theii' Inrni and external 

 ajipearance to good advantage. I'he ligures appended are from iihoto- 

 grajihs which wei'e taken near a west window with the ra\s of tlu' after- 

 K(«nn siin ralliiig directl.v ujion the sin'cinieiis. U is tlu' experience of the 

 Wilier liial Ihis gives more coiilrasi and nial<es liie slmiiialn and the 

 I'l I'itiiecia stand out more indmiiieiiliy in liie piioliiuraiili liiaii is the casL» 

 w liiMi tlie exposure is made in dilTiised light. 



Sixteen species liave been collecte<l thus fai' and (he key has been 

 made to fit the siiecimens at hand witliout regard lo any others. 



