Evans: TAXONOMIC STUDY OF DUMORTIERA 173 
Some of Goebel’s recent observations (6, p. 628, 629) help to 
confirm Schiffner’s deductions. He described a Brazilian Dumor- 
itera, presumably a form of D. hirsuta, which lacked vestigial air 
chambers completely and found that none were formed even 
when the plants were cultivated under the same conditions as 
D. velutina, which developed its normal chambers and papilliform 
cells. He called attention to the fact that very young plants of 
Marchantia lack air chambers and he therefore interpreted the 
Dumortiera without chambers as a juvenile condition. In case 
air chambers are never formed there is simply, in his opinion, a 
persistence of the juvenile state. If air chambers are formed the 
presence or absence of papilliform cells indicates a greater or less 
advance beyond the condition without air chambers. . In other 
words there are certain races or varieties or ‘‘species’’ of Dumor- 
tiera which are never able, even under the most advantageous of 
conditions, to advance beyond the state without air chambers, 
while other “‘species’’ can advance to various stages beyond this 
state. Goebel mentioned also a plant of “D. hirsuta,’ which 
gave rise to an adventive branch without chambers. Since 
“D. hirsuta,” in his conception of the species, normally develops 
chambers, this branch was interpreted a as a reversion to a juvenile 
state. 
According to the writer’s experience, although the three types 
of thallus are often distinctly marked, they are by no means 
invariably so. Even an individual thallus may sometimes bear 
crowded papilliform cells in an older portion and be smooth or 
nearly so nearer the apex; another may form vestigial air chambers 
for a while and then continue its growth without them. Such 
cases are further examples of reversions and indicate that these 
may be induced without the intervention of adventive outgrowths. 
The power to revert, which more or less advanced types thus 
clearly possess, complicates still further the conditions found in. 
the genus and adds to the difficulty of defining specific limitations. 
If a form with crowded papillae represents a ‘‘species,’’ a smooth 
form growing in the same area may represent merely a juvenile 
condition of the same thing or it may represent a “‘species’’ 
which can not advance. At the same time it must be admitted 
that smooth or nearly smooth states are the only ones which 
