PHYCOMYCES NITENS. "2 < 



I"p to this tiiii(> tho spores are surrounded by only a plasma-mem- 

 brane, the spore wall not yet having- been formed. They now l)ei>in 

 to round otf and eontraet, the vacuoles become very nmch smaller, 

 and the whole spore is thereby much reduced in size and surrounds 

 itself with a Avail of considerable thickness. At the time the spore 

 wall is formed the plasma-membranes of the adjacent spores are not 

 in contact, but are separated by the intersporal slime from the vacuo- 

 lar contents. 



The plasma-membranes of the spores, except in the pcnnpheral layer, 

 orio-inate entirelv from the vacuolar membranes, without visil)le 

 change except in form. Only a part of the plasma-meml)rane of the 

 spores in this layer is made up of the original plasma-membrane of 

 the sporangium. In this respect there is a marked diflference between 

 Pliycomycts and Rhizopux. 



The spores vary greath* in size and in the number of nuclei. Every 

 spore has at least one nucleus, and some have as many as twelve or per- 

 haps more. As a rule, there are about six or eight. In PI. V, tig. 25, a 

 and e show the extreme sizes of the spores and 1) the usual size and 

 shape. Uidike Rh'izopux, the walls of these spores are smooth. 



Occasionally the cleavage is interrupted before it is complete, and 

 walls are built around partially divided masses of protoplasm before 

 they have rounded otf sufficiently to obliterate the furrows. This 

 results in peculiar-shaped spores, such as are shown in PI. V, fig. 26, <?, 

 and tig. 27. 



After the spores have been formed the intersporal slime becomes 

 foamy in appearance. (PI. V. fig. 24.) If the sporangium be allowed 

 to dry out and is then placed in water, this intersporal sul)stance swells 

 consideral)ly and probably aids in breaking the sporangium wall. 

 This wall is made up of two layers from a stage even younger than 

 that shown in PL IV, fig. 15, though the walls of the mycelium and 

 the sporangiophores show onh' one laA'er in stained preparations. 



Owing to the great shrinkage of the spores in ripening and to the 

 partial collapse of the columella, the sporangium is very much smaller 

 in diameter when mature than at the time the spores are formed. 



From the time of the cleavage to the ripening of the spores the 

 sporangiophores elongate very rapidly, often reaching a length of 10 

 cm. or more. The ripening usually rec^uires only a few hours. 



As in Bhizo2nis^ the old mycelium is not entirely empty, but con- 

 tains a verv thin layer of protoplasm lying close to the wall, and in 

 this protoplasm are embedded a few nuclei. The columella also in the 

 ripe sporangium contains a loose network of protoplasm with scattered 

 nuclei. The nuclei, while the mycelium is young, have essentially the 

 same structure as those in the spores, except that they often have as 

 many as three nucleoli. As the mycelium grows older, however, they 

 disintegrate like those of Rluzopus. 



