ECOLOGICAL ADAPTATIONS OF CERTAIN FERN PROTHALLIA 487 
gonia. It must be borne in mind that these proliferations result from 
the activity of groups of marginal cells and not from the activity of 
single cells as in the formation of proliferous buds or gemmae, and 
that they do not appear as the result of mechanical injury to the parts 
producing them. 
Summary of Camptosorus rhizophyllus . — The following freatues of 
the prothallial life of Camptosorus indicate to what extent the sexual 
generation of this fern is a factor in its distribution: Mature prothallia 
withstand practically unlimited interrupted drought as found in 
nature, if not exposed to direct sunlight, producing sporophytes 
through fertilization at the time of occasional showers. 
The prothallia may survive exposure to experimental conditions of 
extreme desiccation for periods of four to six days. 
A temperature of — 12° C. is fatal to most exposed plants. 
Where winter exposure does not result fatally, the direct production 
of marginal proliferations may continue the prothallial life indefinitely. 
The following facts concerning spore production and germination 
are also important factors: Spores are shed through a long period 
of time, some being retained in the sporangia until the spring following 
their formation, thus making possible sexual multiplication where 
the winters are too severe for the survival of the prothallia. 
The spores germinate irregularly in point of time, thus offsetting 
the rather greater susceptibility of young prothallia to damage by 
drought. 
ASPLENIUM PLifTYNEURON Oakcs. 
In southern Indiana Asplenium platyneuron Oakes, is very common, 
growing at times on the sides of damp wooded ravines, where fronds 
30-40 cm. in length are not rare, and occasionally in greatly reduced 
form on dry limestone cliffs and ledges. It is most abundant, how- 
ever, in open woods along high ridges and on dry hillsides. The 
presence of many juvenile plants in the last named habitat has sug- 
gested the likelihood of conditions favorable for gametophyte develop- 
ment, and thus led to the present study. Most of the material for 
this work was taken from a steep slope of clay and light humus over- 
lying limestone, with a southeast exposure. No springs are in 
evidence at this place and the hillside is but slightly covered with 
briers and bushes grown up since the timber was cut off three or four 
years ago. 
In general the problem and means of attack are the same as in 
