CERTAIN SPECIES OF Mucor 245 
mentary that it is impossible to know anything besides the sub- 
strata that he used. Among these, the only nutrient, with the 
exception of horse dung and meat, is bread. 
2. TAXONOMIC 
Inasmuch as the early history of the genus Mucor has been 
given in detail by Fischer (1892), we shall begin with the work 
of De Bary (1866). The latter included in Mucor many forms 
which have subsequently been shown to be distinct. For example, 
he attributed ‘‘an apparently irregular pleomorphy of reproduc- 
tive organs”’ to Mucor Mucedo, including and confusing with it 
not only Chaetocladium but also Thamnidium. These somewhat 
startling results, as we have seen before, are to be explained by 
the crude culture methods in vogue in his day. 
Brefeld (1872) made an important contribution to the system- 
atic study of the Mucorales by showing that the polymorphism 
of previous authors did not exist. He it was who first gave us a 
clear conception of Mucor Mucedo, although he (at least in his 
early writings) included Sporodinia, Phycomyces, Rhizopus, Chaeto- 
cladium, and Chaetocladium in the genus Mucor, recognizing only 
one other genus, viz., Pilobolus. However, after studying Chaeto- 
cladium and Piptocephalis in detail he decided that they were 
both generically distinct from Mucor. 
Van Tieghem (1873, 1875) has contributed more to our taxo- 
nomic knowledge of the Mucorales than any other person, but 
practically all of his work lies outside the genus Mucor, he having 
described and named only two species, Mucor plasmaticus and 
Mucor circinelloides. His work, therefore, in so far as the genus 
Mucor is concerned, consisted in defining the genus by removing 
all the closely related genera that were confused with it at that 
time. In his second publication (1875) we have the only reference 
to his idea as to the determination of the species of the genus 
Mucor. He says: “ Depuis plus de trois ans que je m’occupe de 
cette famille, j’ai étudié et cultivé plus de trent espéces de Mucor, 
et souvent encore j’en découvre de nouvelles. Elles se répartis- 
sent en quatre sections. Le filament sporangifére demeure, en 
effet, simple chez les unes, tandis que chez les autres il se ramifie 
latéralement aprés avoir produit son sporange terminal. Ensuite, 
