850 DR, W. R. M°NAB. 
and grows very slowly. The branching is scanty, and only 
after many days the mycelium first sends up a branch to the 
surface which bears spores. Occasionally, after a long 
struggle for existence, the single hypha developed from the 
spore becomes itself aerial and spore-bearing. 
It is not difficult to obtain an idea of the varying forms 
and development of the aerial hypha depending on the nu- 
trition. In the simplest case, when very poorly nourished, 
a basidium forms at the end of the hypha, and thus a 
single row of spores is produced. Brefeld only observed one 
such case as this, although single basidia were sometimes 
observed on mycelia which produced other hyphe with six 
to eight basidia. As arule the hypha branches, as we have 
seen, the first lateral branch being formed immediately below 
the first septum. It develops from twelve to sixteen basidia, 
and is as fruitful as the apex of the main axis of the hypha; 
from the same hyphal cell from two to eight branches may be 
formed, all of which grow to the same size as the main axis, 
and render it indistinguishable. The aerial hypha in this 
case produces a rosette of branches at the apex, all inserted 
at the same height, and each branch ending in rosettes of 
a variable number of basidia. But the development rarely 
stops at this stage. In general a branch is produced im- 
mediately below the second septum from the apex, and 
grows to the same height as the axis; it divides bya transverse 
septum into a terminal and a lower cell, which develop side 
branches like the main axis, or very rarely remain sterile. 
The number of cells may be equal in both or not. Lastly, 
the third joint-cell of the main axis may develop a system 
of basidia. As a rule the lateral branches alternate in their 
position, being placed right and left, and they develop more 
basidia the further they are from the apex. The conidii- 
ferous hyphe thus develop centrifugally, in opposition to 
the mycelial hyphz, which have an apical development. 
Il. Sexual Reproduction of Penicillium, 
In all the instances of the culture of Penicillium 
yet studied the development never proceeded beyond 
the asexual formation of conidia. Other mycologists, as 
De Bary and Tulasne, obtained the same results; and 
Brefeld himself tried the conidia-spores in every kind 
of substratum. At last he employed bread as a sub- 
stratum, as he had found it very useful in his researches 
in the Zygomycetes. A flat piece of common coarse 
bread (not sour) was taken and the spores of Penicil- 
