I0 56 The American Naturalist, [December,, 
self in line with botanical progress. And it may safely be pre-- 
dicted that their influence on the future study of the fungi will be 
of a most positive and fruitful character. 
Assuming, with all writers on the subject, that the simplest and. 
most primitive fungi, which retain undoubted sexual characters, 
the Zygomycetes and the Oomycetes, have been derived from the 
lower Algz, we find them developing, in common with some of the- 
latter, two types of reproductive organs: sexual organs, which 
usually produce resting-spores, and non-sexual organs. Of the 
latter, the sporangium of Mucor may be regarded as the most primi-. 
tive type. In this we finda roughly globular sac of very variable 
size, raised upon a stalk, from whose contents (originally undif- 
ferentiated protoplasm) have been formed, at maturity, a large 
number of rounded spores, varying considerably in size and deter- 
mined, as to their number, by their own size and that of the 
sporangium in which they were formed. The closely related genus. 
Thamnidium? bears similar sporangia at the apices of erect. 
hyphæ, and others of a second sort on lateral branches. These 
latter, known as sporangiola, are essentially only miniature 
sporangia, in which the number of spores has become reduced to- 
four, or even two. In one species of Thamnidium the terminal 
sporangium is often aborted, leaving only the the sporangiolia ; 
and the relative abundance of the two forms can be largely con- 
trolled by varying the conditions of the culture. From this con- 
dition of things it is an easy step to that in which the terminal 
sporangium is habitually suppressed, and the contents of the 
sporangiole have been reduced toa single spore. This condition 
is realized in Chztocladium, whose reproductive organs are no 
wo sporangiola vud set free their spores by rupturing, but.. 
“ closed sporangia ” or conidia. A comparison of the two 
species of Chzetocladium shows the last stage in the reduction.. 
In C. fresenianum the conidium begins its germination by 
throwing off its outer coat, a process morphologically equivalent. 
to the rupture of the sporangium-wall ; but no such preliminary 
? The forms referred to in the following pages will nearly all be found described, and ~ 
red, in the English Le oa of DeBary’s “Comparative Morphology of the: 
y 
Fungi,” published by Macmillan & © 

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