7 6 



while the paraphyses have at least several transverse septa, as well 

 as being branched in some cases. There is a difference of opin- 

 ion as to the origin of spore-sacs, some authors (Schwendener, 

 Fuisting) maintaining that in all cases they take their origin from a 

 specialized hyphal tissue having no connection with the hyphae pro- 

 ducing the paraphyses, this hyphal tissue being known as asco- 

 genous hyphae, and always recognizable by its blue coloration 

 with iodine after treatment with potassic_ hydrate. Other authors 

 (Sturgis) deny the existence of a special ascogenous tissue. As far 

 as my observations go it seems that the hyphae terminating in spore- 

 sacs are different in structure from the hyphae from which the 

 paraphyses are formed, being thicker and more irregular in shape. 

 In most cases it was, however, impossible to distinguish such a 

 tissue, either microscopically or by the aid of the iodine reaction. 

 In no case could it be definitely proven that the spore-sac bearing 

 hyphae were entirely distinct from those bearing paraphyses, both 

 seeming to arise as branches from the same hyphal system. 



As the apothecium increases m size it causes the superimposed 

 structures of the thallus to bulge upward and finally to rupture. In 

 immersed apothecia the opening thus formed in the thallus is small, 

 while in lichens with free apothecia the superimposed tissue is re- 

 moved, or remains in part in a fragmentary form upon the thecium 

 (see Epithecium). 



After the apothecium has broken through the thallus it may con- 

 tinue development either with or without concomitant changes in the 

 thallus ; in the one case the portion of the thallus immediately sur- 

 rounding the true exciple grows with the latter structure, so that the 

 mature apothecium is enclosed by a cortical, algal and medullary tissue 

 continuous with that of the thallus, the growing apothecium no doubt 

 acting as a stimulus which causes the surrounding area of the thal- 

 lus to take on renewed cell-activity. In the other case the thallus 

 is not affected by the apothecial growth, the apothecium simply 

 forcing its way through the thallus and continuing to grow, some- 

 times developing a long stipe, on the top of which the apothecium is 

 borne (Cah'aum, Coniocybe). There are all gradations between 

 the forms in which the thallus takes no part in the formation of the 

 apothecium and in which it even precedes the margin of the proper 

 exciple. The thalloid exciple serves to increase the assimilative 

 function, which is demanded by the increased cell-proliferation in- 

 volved in the formation of the apothecium. 



