16 FORMATION OF SPORES OF RHIZOPUS AND PHYCOMYCES. 



The growing ends of the stolon.s are densely crowded with proto- 

 pUisni containing many nuclei. This condition prevails for sonic dis- 

 tance back in the stolons (PL I, fig. 2), but as we follow back toward the 

 older part the protoplasm is more and more permeated with cell sap, 

 and at last we find a region where there is nothing Imt a wall filled 

 with cell sap, so far as we can distinguish from a surface view of liv- 

 ing material. In stained sections, however, as shown in PI. I, fig. 3, 

 it can be seen that there is still a thin layer of protoplasm lining the 

 wall, and strands or even small masses of it in the center. In parts 

 as old as that shown in the figure, the nuclei have begun to disinte- 

 grate somewhat, and appear as tin}' red-staining masses of various 

 shapes. (PI. I, fig. 4.) . 



The young sporangiophores, like the ends of the stolons, are densely 

 crowded with protoplasm and nuclei, and even the lower part of the 

 older ones is never entirely devoid of protoplasmic contents, as is 

 stated b}^ Leger, but retains a structure very nmch like that in the 

 stolons. 



As the sporangiophore reaches its full length it ])egins to swell out 

 at the tip into a tiny round body, the future sporangium. The con- 

 tents of this are at first evenl}^ distributed, being equall}^ dense in the 

 center and at the periphery, but before it has reached half its final 

 size the protoplasm begins to be decidedly dense toward the sporan- 

 gium wall, while in the center it is of a nuich looser structure. PL I, 

 fig. 5, shows the distribution of the cytoplasm and nuclei at this stage. 

 There are also present a few crystalloids. They seem often to be in 

 tiny clear vesicles, but whether or not these are ordinary vacuoles I 

 can not be certain. These crystal-like bodies vayj nmch in size, and 

 as a rule increase in number as the sporangium gets older. It is quite 

 noticeable, however, that the}^ are entirely confined to the central part 

 of the sporangium. 



The nuclei are so small that they appear only as dots in a drawing 

 of the size of PL I, fig. 5. Their structure can, however, be clearly 

 made out with higher magnification, and it is to all appearances pre- 

 cisely like that of those shown in PL II, fig. 0, which will be described 

 later. 



The cytoplasm in young sporangia, it will be observed, is quite 

 dense next the sporangium wall, but gradually becomes less dense 

 toward the center, where it is of a very loose spongj' structure, con- 

 taining many vacuoles of considerable size. There is at this stage no 

 sharply defined boundar}' l)etween the denser and the less dense parts 

 of the cytoplasm, but a gradual transition from center to periphery. 

 The denser la} er does not, however, extend quite to the sporangio- 

 phore at the base of the sporangium. (PL I, figs. 5 and 6.) 



At this time also there is a very marked streaming of the protoplasm 

 up the sporangiophore into the sporangium. These currents appear 



