SOME ECOLOGICAL ADAPTATIONS OF CERTAIN FERN 
PROTHALLIA— CAMPTOSORUS RHIZOPHYLLUS LINK., 
ASPLENIUM PLATYNEURON OAKES. 
F. L, Pickett 
The part played by the prothalha in the ecological history of ferns 
has been given but little attention. If the studies on apogamy and 
related phenomena be left out of consideration the work along this 
line is very limited indeed. What work has been done may be ar- 
ranged in three groups, as it has had to do with the increase of growing 
points by branching of the prothallia or by the production of special 
proliferations, the influence of light upon the germination of the spore 
and the development of the prothallium, the influence upon the pro- 
thallia of variations of water supply. 
(A) Goebel (II: 197-210) has summed up che findings concerning 
the vegetative increase of the prothallia of homosporous ferns. Briefly 
stated there are two general types of growth, thai: which leads to the 
formation of a more or less regular heart-shaped plant, and that which 
leads regularly to considerably branched forms. Of the second group 
the Vittariaceae and Hymenophyllum show a lobular or ribbon-like 
body which arises by the branching of a simple primary cell plate. 
In Trichomanes, also of the second group, the prothallium is a mass 
of more or less branched filaments. With reference to those forms 
which regularly develop heartshaped prothallia Goebel (II: 203) 
says: "Young fern plants which have not yet formed typical meristem 
easily pass over again into the filamentous stage in feeble illumination. 
... In older prothallia this only takes place if they have lost their 
meristem and are enfeebled by unfavorable environment. Commonly 
these conditions result in the production of pluricellular shoots." 
To this last group mentioned by Goebel belong the plants often cited 
as producing adventitious outgrowths following mutilation in hybridi- 
zation experiments. This author also mentions a case of proliferation 
by adventitious shoots from the base of an old prothallium of Osmunda 
regalis (loc. cit. I: 49). More recently several authors have found 
477 
