Classification of Ohio Ascomycetes 
15 
to the substratum by rhizoids and are almost wholly dependent on the 
host for nourishment. From such a primitive form of ascomycete, there 
could be two lines of descent, one of which would give rise to higher 
lichens with foliose and fruticose thalli, close relationship with the algal 
host, and the apothecial form of ascocarp retained, while the other 
would produce the lower lichens which are crustose upon the substratum 
or sunken into it and which live in increasingly loose relations with the 
algal host as they sink into the substratum. Some of these forms could 
have lost the algal habit gradually as they came into closer and closer re¬ 
lationship with the substratum and so have given rise to non-algicolous 
ascomycetes. As a rule, lichens which have perithecia or hysterothecia 
are those that are sunken into the substratum, while those that are 
crustose upon the surface, or are foliose or fruticose, usually have 
apothecia. On the theory that the apothecium is the primitive form of 
ascocarp, perithecia and hysterothecia would arise as protective struc¬ 
tures in reaction to xerophytic habit or sinking into the substratum. Of 
course we may begin with such a form as Ascobolus carbonarius, 
suppose that it evolved a form having the algicolous habit, and then 
apply the above reasoning equally well. Therefore, the rather unim¬ 
portant question whether primitive ascomycetes were lichens or not, is not 
so easy to settle, though it is reasonable to suppose that certain 
Rhodophyceae which had become parasitic on other marine algge may 
have acquired a terrestrial habit, passed into parasitic relationship with 
terrestrial algae, and acquired the ascomycetous forms of reproduction 
and carpologic structure as a response to changed conditions of environ¬ 
ment. The relation of the lichen to its algal host and to the substratum 
touches this problem and is discussed in a previous paper (Fink 31). 
To generalize from finding one or two plants which have apothecia 
and at the same time possess reproductive areas and processes much like 
those found in the Rhodophyceae would be a very uncertain procedure; 
but the discussion by Dodge (24) shows plainly that the generally 
favored theory that the perithecium is the primitive form of the ascocarp 
rests on very uncertain evidence at best. While it is certain that many 
careful studies of carpologic structure and development will be neces¬ 
sary before we may know with any reasonable degree of certainty 
whether the apothecium or the perithecium is more primitive, it has 
seemed reasonable, in view of all the evidence at hand, to adopt a 
sequence of orders of ascomycetes which comports in a general way with 
the view that the apothecium is the primitive form of ascocarp. In fol¬ 
lowing this view, it has seemed best to place the algicolous discomycetes 
