Heterothallism and similar phenomena 11 
Blakeslee himself recorded in 1915 the formation of so-called 
imperfect hybrids, i.e. the partial union of reproductive bodies, when 
he grew dioecious species of Zygorhynchus between a + and a — 
Mucon 9 ,10). The plus form showed imperfect fusions with the larger 
gamete of the Zygorhynchus, and the minus form with the smaller. 
On these grounds the plus race is regarded as the male-bearing 
thallus and the minus race as the female. The same opinion had 
already been expressed by Blakeslee from other considerations. It 
is a debated point whether these gametes of Zygorhynchus can be 
regarded as male and female in the usual sense, for it has been claimed 
that the contents of the larger cell are emptied into the smaller cell. 
Gruber ( 25 ) regards the larger as male and compares the process with 
that taking place in the Oomycetes. These results obtained by 
Gruber have been criticised by Moreau ( 34 ) who is of the opinion that 
the process in Zygorhynchus falls into line with the rest of the Mu- 
corines, and that Gruber has erred through misinterpreting the 
position of the suspensor. 
A point of further interest arises when it is found that G. F. 
Atkinson(l) holds that the larger cell in Zygorhynchus, supposed by 
him to be female, is provided with a trichogyne by means of which 
connection is made with the male organ, the smaller gamete. 
Atkinson also holds that Zygorhynchus is a lowly form of Ascomycete 
and a connecting bridge between this group and the Zygomycetes. 
It is not our purpose here to discuss the origin of any fungal group, 
but if Zygorhynchus be regarded as an Ascomycete the partial fusions 
with heterothallic Mucorines are even more difficult to explain. 
A similar cross-septum has been reported in Zygorhynchus by 
Gruber ( 25 ), who also comments on its temporary nature but attempts 
no morphological interpretation. Further cytological observations 
should clear up these difficult points. 
Burger ( 14 ) has recently been working on strains of Cunning- 
hamella. He was unable either to get his results to fit those of 
Blakeslee or to suggest an alternative theory. I have specially men¬ 
tioned this work for it is probably through an examination of such 
aberrant cases that further light will be thrown on the whole problem. 
Careful cultural experiments with species having uninucleate spores 
(and occasional multinucleate ones), and a comparison with multi- 
nucleated spore species, especially with regard to their hetero¬ 
thallism and heterogamy, would probably be helpful also. 
No attempt will be made here to deal with the question of the 
methods of reproduction amongst the Myxomycetes. The Oomycetes, 
