Igr0] MOTTIER—SEX OF ONOCLEA 233 
abortive. It was thought at one time in this study that the 
smaller spores were the ones that produced the purely antheridial 
prothallia, but sowings were made by selecting, in so far as possible, 
the more vigorous spores (an extremely tedious process), but the 
results did not bear out the expectation. Owing to the difficulties 
of selecting individual spores, it is not maintained that the last- 
named experiment is of any great value, at least the writer does 
not lay any stress upon the results. It seems reasonable that a 
larger percentage of the smaller spores, that is, those which show 
less chlorophyll and which germinate less readily, would fail to grow 
than in the case of the larger ones, so that the possibility of the 
smaller and abortive-looking spores producing chiefly male pro- 
thallia is not excluded. However, on this point the writer can 
make no definite assertions. 
The foregoing statements may be summarized as follows: 
1. The spores of Onoclea Struthiopteris when grown upon earth, 
under optimum cultural conditions, produce regularly three kinds 
of prothallia: small plants bearing only antheridia, the so-called 
male gametophytes; larger prothallia bearing only archegonia, the 
female gametophytes; and those bearing both archegonia and 
antheridia, the bisexual or monoecious prothallia. 
2. Archegonial prothallia, which continue growth without 
bearing a sporophyte, sometimes develop numerous small lobes 
from the older portions, upon which numerous antheridia appear. 
3. The gametophyte, therefore, is not strictly dioecious, and 
there is in all probability no sex-determining chromosome. 
4. It is highly probable that the development of purely male or 
female gametophytes is not dependent upon conditions of nutrition, 
but that the sexual tendency is predetermined in the spore. 
Environmental conditions, or the failure of an egg to give rise to 
a sporophyte, owing to a lack of fecundation, may induce the 
development of antheridia upon archegonial plants, which continue 
their growth for some months. 
5. Pure males result, in so far as is known, under good cultural 
conditions from the dominance of the male tendency in the spore 
over the female tendency. 
Inprana U2 SITY 
BLoomincton, INDIANA 
