STRUCTURE. 55 



form particular, often tun-like or globular cells ; the longer ones 

 are changed, through the formation of cross partitions, into 

 chains of similar cells ; the latter often attain by degrees strong, 

 thick walls, and their greasy contents often pass into innumerable 

 drops of a very regular globular form and of equal size. Similar 

 appearances show themselves after the sowing of spores, which 

 are capable of germinating in the medium already described, 

 from which the air is excluded. Either short germinating 

 utricles shoot forth, which soon form themselves into rows of 

 gemmules, or the spores swell to large round bladders filled 

 with protoplasm, and shoot forth on various parts of their 

 surface innumerable protuberances, which, fixing themselves 

 with a narrow basis, soon become round vesiculate cells, and on 

 which the same sprouts which caused their production are re- 

 peated, formations which remind us of the fungus of fermenta- 

 tion called globular yeast. Among all the known forms of 

 gemmules we find a variety which are intermediate, all of which 

 show, when brought into a normal condition of development, 

 the same proportion, and the same germination, as those we first 

 described. 



We have detailed rather at length the structure and develop- 

 ment of one of the most common of the Mucors, which will 

 serve as an illustration of the order. Other distinctions there 

 may be which are of more interest as defining the limits of 

 genera, except such as may be noticed when we come to write 

 more specially of reproduction. 



ASCOMYCETES. Passing now to the Ascomycetes, which are 

 especially rich in genera and species, we must first, and but super- 

 ficially, allude to Tuberacei, an order of sporidiiferous fungi of 

 subterranean habit, and rather peculiar structure.* In this order 

 an external stratum of cells forms a kind of perithecium, which 

 is more or less developed in different genera. This encloses the 

 hymenium, which is sinuous, contorted, and twisted, often forming 

 lacunae. The hymenium in some genera consists of elongated, 

 nearly cylindrical asci, enclosing a definite number of sporidia; 

 in the true truffles and their immediate allies, the asci are broad 

 * Vittadini, " Monograptria Tuberacearura, " 1831. 



