ZYGOMYCETES 339 



same structure as those that follow them. They are globular sacs borne 

 at the end of sporangiophores, and the spores produced within them are 

 never endowed with the power of active movement. The different 

 forms of sporange and sporangiophore afford characters for the genera 

 of the group. Mucor (Michel.), Pilobolus (Tode), Sporodinia (Link), 

 Phycomyces, Rhizopus (Ehrenb.), Circinella (Van Tiegh.), and Absidia 

 possess a peculiar conformation of the basal wall of the sporange. It 

 bulges inwards in a conical or more or less oval form (see fig. 293 A), and 

 presents an appearance which has suggested the name of columel for 

 this peculiarity. Of 'the genera possessing a columel some are dis- 

 tinguished by a fugacious sporangial wall, others by a firm persistent 

 one, while the mode of branching of the sporangiophore (or the absence 

 of branching) and its general form, aiford other generic characters. 

 Morti.erella has a fugacious sporangial wall but no columel. Tham 

 nidium (Link), Chaetostylum (Van Tiegh.), and Helicostylum (Cord.) 

 have two kinds of sporange, the one kind like those of Mucor, and 

 the other smaller (sporangioles) with a persistent wall, no columel, ' 

 and containing but a few spores, which however resemble the others in 

 function. 



On old and on badly nourished myceles of some species, accessory 

 propagating bodies are formed (chlamy do spores, stylospores, &c.). All 

 such accessory spores are capable of giving rise to normal characteristic 

 myceles either at once or after a period of rest. In Mortierella single 

 acrospores are borne on slender mycelial hyphae. The old myceles and 

 even the sporangiophores of Mucor break up into resting-cells like those 

 of Saprolegnia with thick walls. The chlamydospores (Van Tieghem) of 

 Mortierella are such bodies, and where they occur terminally, de Bary 

 regards them as transitional forms to the acrospores of the same genus 

 just mentioned. Brefeld and Van Tieghem have described (Mucor 

 racemosus, Fres., &c.) another form of accessory propagating spores, 

 which are produced in series or chains through transverse division of 

 the mycelial hyphae. These either remain joined together in conferva 

 fashion, as Berkeley says, or they part company, and each such cell 

 exhibits a yeast-like vegetation. 



Sub-order 2 : CH^TOCLADIE^E. The mycelial hyphae of Chaetocladium 

 (Fres.) become attached to the hyphae of the Mucor-host, and, by the 

 resorption of the cell-wall at the place of contact, effect a direct com- 

 munication. At such places of attachment a large number of globular 

 protuberances are produced close together, forming a body of consider- 

 able size, which may be regarded as a food-reservoir. The act of con- 

 jugation and the formation of the zygosperm agree in all essential par- 

 ticulars with the corresponding processes in the Mucoreae. The intine 



z 2 



