PLUS AND MINUS STRAINS IN THE GENUS GLOMERELLA 253 
The process of fertilization has not been studied to any great 
extent as yet and it is impossible to explain with certainty the phe- 
nomena which have been described in this article. However, a theory 
that would seem to explain the facts described may be of interest. 
The minus strain produces an abundance of perithecia and it would 
seem that this is the strain that produces the oogonia and might be 
designated as the female strain. As most of the perithecia remain 
immature or at most but poorly developed, it would seem as if the 
antheridia in this strain were mostly lacking or poorly developed so 
that the stimulus following the fertilization is not sufficient to bring the 
perithecia to maturity. With special stimulating media, the antheridia 
are possibly better developed or else the stimulating effect of the 
medium added to that of the fertilization is sufficient to bring some of 
the asci to maturity. In the plus strain, it is probable that the 
antheridia are produced very abundantly while the oogonia are pro- 
duced only sparingly, and where the latter are produced the perithecia 
form in masses. If the two strains are brought together on the same 
plate, fertilization takes place and a profuse development of perithecia 
follows. 
It would seem that we have conditions in this group somewhat 
intermediate between conditions usually found in the Mucorineae. In 
such fungi as Rhizopus nigricans, only one set of the sexual organs is 
produced on a single strain and the presence of both strains is necessary 
for the production of the zygospores; while in species like Sporodinia 
grandis, both sexual organs are produced on the same strain. In the 
Glomerella fungi we have forms in which a fertilization between 
strains is not necessary for, but stimulates the production of the 
sexual stage. 
Whether other forms of the ascomycetes may be found in which a 
fertilization between different straias stimulates the development of 
the fruit body and ascospores is a question. The Glomerella forms 
show so much variability that it is possible that we have in the cul- 
tures that have been described merely isolated variations that may 
not be common in the ascomycetes as a group or even within the 
genus Glomerella itself. Yet the fact that two sexual strains may 
sometimes be present adds another factor to be considered in all 
work dealing with the development of ascogenous stages. 
Louisiana Agricultural Experiment Station, 
Baton Rouge, La. 
