MUCOR RACEMOSUS FRES. 



Kx \\". P.. GRO\'E. M.A. 



Bofiinical Laboratory. Municipal Technical School. Birniiii'^hani. 



On looking at the text-books of Fungi and the Fungus-Floras 

 pubUshed in this country, one is struck by the almost total 

 absence of any reference to Mucor raccniosus, although it is 

 frequently referred to in books on fermentation and brewing. 

 Yet this species is one of the most widely-spread of the Phyco- 

 mycetes. and must be 

 frecjuently met with : but 

 --^ it is. no doubt, mistaken 



<^ for something else, just 



as Rhizopiis nigricans 

 is constantly seen mount- 

 ed on microscopic slides 

 with the label, " Mncor 

 mitcedo Linn." The 

 fault lies, perhaps, in 

 the absence of any good 

 description of the fimgiis 

 in an accessible publica- 

 tion — a want which the 

 following notes may 

 possibly supply. 



ill. racemosns is met 

 with on all kinds of 

 substrata, on starch- 

 paste, potatoes and the 

 like ; on rotting \ege- 

 tation. dried fungi, and 

 herbarium specimens ; and 

 also on dung, mixed with 

 M. niiicedo ; on meat and 

 on dead flies lying in water. 

 It is a frequent weed in the 

 cultures of the inexpert bacte- 

 riologist in Petri-dishes and 

 similar preparations. On the 

 latter it forms a thin stratum 

 of a pale fawn colour or buffy- 

 brown. seldom more than half- 

 an-inch in depth, often con- 

 siderably less. 

 In order to 

 with certainty 

 premised that 

 Mncor can be 

 two distinct 

 the division 



A 



Figure 3. 



sporangium emptied of 

 its spores, X 500. 



Figure 1. 



The terminal por- 

 tion of a branched 

 hypha, X 60. 



^ 







o 



Figure 6. 



Chlamydospores in 



the mvceUum. 



X'250. 



Figure 4. 

 Spores. X 500. 



Figure 2. 

 -A single lateral 



recognise it 

 it must be 

 the genus 

 divided into 

 sections : fir.st. 

 Mono -mncor. 



Figure 5 



sporangium, X 250. 



in which the sporangiophore is, 

 with rare exceptions, always 

 unbranched ; and, second, a 

 division in which the sporangiophore is always branched, 

 except when it is \ery young. The branched forms may be 

 further sub-divided into two sections — Raccnioinucor, in 

 which the main hypha remains clearly distinct and the branches 

 distinctly lateral, i.c- it branches monopodially — and Cymo- 

 inncor. in which the main hypha is frequentlv thrust to one 

 side and overtopped by the originally lateral branch, i.e. it 

 branches sympodially. But these two sections are not always 

 so distinct as might be imagined ; some species in fact 

 combine both modes of branching in the same groVvth. 

 M. racemosns, as its name implies, belongs to the sub- 

 division Racemo-nincor : M. mnccdo belongs to Mono-mncor. 

 and is much taller, reaching a height of even se\eral inches. 



The sporangiophore of M. raccniosus is erect and colourless, 

 with many short, simple. Literal branches, each of which bears 

 a sporangium smaller than that of the main hypha, and is usually 

 nearly straight or bent slightly downwards (Figure 1). 

 Abo\e the insertion of each branch there is a septum (Figure 2). 

 The sporangia are small, round, \aryiug much in size, (average 



-■V germinating 



chlamydospore, 



X 250. 



40 A't, erect or nodding, .\ellowish or yellowish-brown, never 

 black, but always semi-transparent so as to allow the spores 

 to be seen through the membrane. The membrane is smooth, 

 but slightly raised in rounded bulging elevations by the outer 

 spores of the contained mass : the most striking difference 

 from M. niuccdo is seen 

 in the fact that, on the 

 addition of water under 

 the cover-slip, the mem- 

 brane does not instantly 

 break up and vanish, as 

 in the latter, but merely 

 splits from the pressure 

 and remains otherwise 

 intact (Figure 3). It is 

 yellowish, and finely punc- 

 tate all o\er with minute 

 crystals of oxalate of lime, 

 which do not assume 

 the needle - Uke shape 

 found in .11. mnccdo. 



The columella is round- 

 ish or ovate, smooth, 

 and occupies from one- 

 twelfth to about one- 

 fourth of the sporangial 

 cavity. 

 The spores are roundish or 

 shortly elliptic, 5-S /(x broad, 

 6-10 M long, smooth, singly 

 colourless, but slightly yellow- 

 ish in mass (Figure 4). 



The most persistent mark 

 of distinction, however, Ues in 

 the fact that all parts of the 

 mycelium are pro\ided with 

 a great abundance of chlamy- 

 dospores. -A. chlamydospore 

 is a portion of the protoplasm 

 of the mycelium which sepa- 

 rates itself from the rest, 

 surrounds itself with a cell- 

 wall, .and becomes a kind of 

 resting-spore, which can in 

 suitable circumstances ger- 

 minate and produce a myce- 

 lium or even a minute sporan- 

 giophore directly (Figure 5). 

 The\- correspond to what are 

 called aplanospores in the Algae. The chlamydospores 

 of M. racemosns lie in long rows in the hyphae (Figure 6), 

 and e\en in the sporangiophore ; when young they are 

 rounded and highly graiuilar. afterwards they become oval 

 or barrel-shaped, and are easily distinguished by their 

 refringent contents and their thick, smooth, colourless, and 

 many-layered cell-wall. 



If a portion of the mycelium of this species is submerged in 

 a sugary fluid it transforms itself into a mass of ferment-cells 

 (Figure 7). These cells are roundish; they produce buds like 

 yeast cells, and like them excite fermentation in the saccharine 

 solution. M. mucedo possesses neither chlamydospores nor 

 ferment-cells. M. mnccdo cannot invert saccharose, in fact 

 M. racemosns is almost the only Mncor that can do so. 



Both these fimgi are abundant everywhere, .and ha\e been 

 described by authors in the older books on fungi, each 

 under more th.an a dozen names. The figures and description 

 here given will, howe\er, enable anyone to recognise 

 M. racemosns without the slightest difficult)-. 



Figure 7. 



Ferment cells, 



X 250. 



361 



