100 COMPARATIVE MORPHOLOGY OF FUNGI 



with a plasma membrane which is thickened into a wall on the side toward 

 the stipe (Fig. 58, 7). 



The central portion next the stipe remains sterile and becomes the 

 columella. Its nuclei no longer show any membrane or nucleoli and 

 degenerate, although occasionally fusions and amitotic divisions may 

 appear. The peripheral spherical cap forms the fertile sporogenous layer. 

 These types are distinguished according to the manner of spore 

 formation. In the first type, Pilobolus crystallinus, (P. microsporus) and 

 P. oedipus (Harper, 1899), the whole spore protoplasm is first split by 

 vacuolization into uni-, rarely multinucleate, portions, the so-called pro- 

 tospores (Fig. 58, 5); these round off (Fig. 58, 6), swell, undergo several 

 nuclear divisions (Fig. 58, 7) and are then divided into multinucleate 



portion by cleavage (Fig. 58, 8 to 10). 

 These portions again round off, are sur- 

 rounded with a membrane and become 

 two-spored (Fig. 58, 11). 



In Circinnella conica (Moreau, 1913) 

 and C. minor (Schwarze, 1922) develop- 

 ment is simpler; here the protospores 

 without further splitting are surrounded 

 by membranes and become spores di- 

 rectly. In most of the other genera, as 

 Fig. 59. — Sporodiniagrandis. Ver- in Sporodinia (Harper, 1899) Phycomyces, 



an^m^TAft^arpe^lsm "^ RMzo P us > Mucor, Absidia and Zygorhyn- 



chns (Swingle, 1903; Moreau, 1913; 

 Green, 1927) the protospore stage is omitted. The division of the nucleus 

 in Phycomyces, probably also in the other genera, occurs simultaneously in 

 the whole sporangium. Hereby the sporogenous protoplasm splits 

 directly into multi-, rarely uninucleate portions which round off, sur- 

 round themselves by a membrane and develop directly to spores without 

 further nuclear division (Fig. 59). 



The sporangiospores are unicellular, generally ellipsoidal or spherical, 

 hyaline or dully colored; they lie either free in the sporangium or are 

 embedded in a finely granular intermediate substance, swelling gel-like 

 in water, which is probably developed within themselves (Fig. 5, 2). At 

 germination they swell considerably and develop into a mycelium through 

 one or more germ tubes. Their morphological characters are not yet 

 clear. One can either regard them as analogous to the zoospores of the 

 Oomycetes, i.e., as akinetes which because of incomplete cleavage have 

 remained large and multinucleate; or one can, probably with more reason 

 on the basis of the parallelism in protospore formation between Pilobolus- 

 Sporodinia and the Synchytrium decipiens-S. Taraxaci series, regard the 

 sporangiospores as reduced sporangia and the Mucor sporangia are 

 reduced sori. As in Synchytrium and Urophlyctis alfalfae the contents 



