CHAPTER V. COMPARATIVE REVIEW. MUCORINT. 155 



shaped cells, which often acquire thick membranes and then under favourable 

 conditions of vegetation and in many cases after a long resting period develope 

 into normal mycelial tubes. These cells are densely filled during their resting 

 period with tolerably homogeneous protoplasm ; but sometimes, and especially 

 in starved or dying or dead specimens, numerous large drops of oil may become 

 separated in the protoplasm, a circumstance which once gave occasion to some 

 passing misapprehensions 1 . On old mycelia especially, and in species of Mucor on 

 sporangiophores also, the protoplasm of which is usually employed in forming gonidia 

 of other kinds, these gemmae occur frequently as cylindrico-ellipsoid cells inserted like 

 stoppers at irregular intervals in hyphae which are otherwise without protoplasm 2 . 

 They occur frequently in many species, especially in those of Mucor; in some, 

 as Chaetocladium, Piptocephalis, and Phycomyces, they have not yet been observed. 

 In old cultures of Pilobolus they make their appearance on the slender branches of 

 the mycelium especially, and not unfrequently in thick swellings in them, which 

 if vegetation is continued develope into typical sporangiophores ; they resemble in fact 

 incipient sporangiophores which have remained stationary at the first stage of their 

 development and have become dormant, and have a thick yellowish brown outer mem- 

 brane and dense reddish yellow protoplasm; they are liable to be mistaken for zygo- 

 spores, and grow when they germinate into typical gonidiophores. The smooth-walled 

 ' chlamydospores ' of Mortierella, described by Van Tieghem, also belong to this 

 class. Those which are not intercalary but terminal in the mycelial hyphae are 

 obviously transition- forms to the acrogonidia mentioned above. 



Under certain conditions of vegetation some of the Mucoreae also form 

 gemmae, which may be distinguished from the preceding by the names of chain- 

 gemmae and sprout-gemmae. These forms have been most thoroughly studied 

 in Mucor racemosus and have been described by Brefeld 3 , but they occur also, 

 according to Van Tieghem, in other and very different species. The formation 

 of these gemmae begins when the mycelium is submerged in a nutrient fluid, 

 especially in a saccharine solution capable of alcoholic fermentation, and is thus 

 cut off from the. free access of oxygen. Numerous transverse walls divide the 

 entire mycelial tubes into short segments, which may be narrowed into mere disks 

 and are swollen with protoplasm. The segments may, as Berkeley 4 said in 1838, 

 remain united together in a confervoid manner or separate from one another, and, if 

 the conditions remain the same, they often sprout luxuriantly after the manner of the 

 Sprouting Fungi described on p. 4. If spores are submitted to the same conditions, 

 they first swell into large spherical vesicles and then sprout directly without first 

 forming germ-tubes. The sprouts which proceed from them have almost, if not quite 

 always, the form of spherical vesicles which grow to more than 40 ft in diameter and 

 repeatedly put forth new generations of sprouts by copious development at all parts 

 of their surface ; the new sprouts either continue united together or some of them 

 separate from one another. This sprouting form of Mueor was formerly known as 



1 See Bot. Ztg. 1868, p. 765. 



2 Bail in Flora, 1857, t. XIII. Zabel in Melanges biolog. Acad. de St. Petersbourg, III. 

 Brefeld in Thiel's Landw. Jahrb. V (1876), p. 282, t. i. See also the works cited below passim. 



3 Landw. Jahrb. V (1876). Id. in Flora, 1873. 



4 Mag. of Zoology and Botany, II, p. 340. 



