68 MORPHOLOGY OF THE MUCORS. 



§ 235.— Subdivision of the Mucor family. 



From the explanations in the preceding paragraphs, the 

 MucorarecB may be defined as Zygomijcetes which exhibit spor- 

 angial, but not conidial, fructification, and produce naked 

 zygospores. This family may be subdivided into three sub- 

 families, of which, however, only one falls within the scope of 

 the present work, whilst the others will merely be referred to 

 in order to facilitate comprehension of the connection existing 

 between them. 



The sub-family of Thamnidieae is characterised by the posses- 

 sion of two kinds of sporangia : on the one hand, a large, 

 normal, polysporous sporangium, on the crown of the sporangio- 

 phore (terminal sporangium) ; and, on the other hand, certain 

 far smaller sporangia, which are situated lower down and put 

 forth by whorled lateral branches of the sporangiophore. This 

 second kind of sporangia are destitute of columella, contain only 

 a pair of endospores — sometimes only a single one — and are 

 known as sporangioles. The most closely investigated member 

 of this sub-family, Thamnidium elegam, is shown in Fig. in. 

 Starting from observations conducted by Brefeld (IX.), the 

 dependence of fructification, in this species, on the external 

 conditions (chemical composition and concentration of the 

 nutrient substratum ; temperature) was examined by J. Bach- 

 MANN (I.). This worker demonstrated that, by controlling these 

 conditions, it is possible to compel the fungus to produce either 

 terminal sporangia or sporangioles exclusively, or both together, 

 or again to remain barren of fruit. 



The second sub-family of the Mucoraeece, namely, the 

 Pilobolese, is distinguished by the featiu-e that the ripe spor- 

 angium — owing to its peculiar structure — is released, and even 

 forcibly expelled from, the organ on which it has been developed. 

 Of the species belonging to this group, mention may be made 

 of Piloholus cri^stallinus, which is often found on horse droppings. 



Finally, tlie Mucorese constitute the third sub-family. They 

 are distinguishable from the first by producing only a single 

 kind of sporangia, which, unlike those of the second sub-family, 

 do not separate from the sporangiophore before discharging 

 their contents, but remain attached thereto after bursting. 

 The discharge is effected in consequence of either the lique- 

 faction or brittleness of the membrane of the ripe sporangium. 



One of the genera in this third family, viz. the genus 

 Sporodinia, is characterised by the forked branchings of its spor- 

 angiophores and the suspensores of the zygospores. This form 

 is represented in Fig. 107. On the other hand, in all the re- 

 maining Mucorece — which have been arranged into five genera 

 by A. Fischer (III.) — these organs are either not branched at. 

 all or at least not forked. 



