AND INHERITANCE IN PEDIASTRUM. 395 



2. Cell division by repeated bipartitions in general according to 

 the principle of rectangular intersections. 



3. Escape of the vesicle contemporaneous with quiverings and 

 then slow writhings of the swarmspores for a very brief period, 

 passing at once into 



4. The free-swimming stage, lasting several minutes, in which 

 the swarmspores dart about in entire freedom from each other. 



5. Slow writhing stage, in which the swarmspores gradually 

 perfect the spatial interrelations found in the adult colony. 



The description of reproduction just given may be regarded as 

 representing the process near its optimum as to speed and efficiency. 

 The resulting young colonies (Figs. 15-17) are fairly regular in 

 the arrangement of their cells and rounded in outline. Such con- 

 ditions are as a rule only achieved in the case of colonies favorably 

 situated and brought under observation only a short time before 

 swarming occurs. In the case of colonies sealed under a cover glass 

 as described above for from six to twenty-four hours before repro- 

 duction occurs there are some marked modifications in the process 

 which lead to characteristic changes in the shape of the young col- 

 ony. One of the commonest deviations from type in the colonies as 

 found in nature is seen in the tendency to be oblong or oval instead 

 of circular in outline. The explanation of this modification in form 

 can be discovered at once by observing the reproduction of colonies 

 which are unfavorably placed. As noted, divison and swarming 

 may sometimes be completely inhibited if the colonies are mounted 

 under a cover glass and sealed before they are full grown. If, how- 

 ever, they are about ready to swarm and, for example, are mounted 

 some time in the night before the morning on which they would nat- 

 urally swarm, the process may take place later in the day. Swarm- 

 ing may thus be delayed for several hours and in such cases it is at 

 once seen that it is less vigorous. 



The free-swarming period is shorter or may disappear entirely, 

 the swarmspores only writhing and twisting about without really 

 getting out of contact with each other. The whole active stage is 

 shortened. This may go so far in certain media that the swarm- 

 spores scarcely move at all ('88). The fact is to be at once observed 

 in all such cases of a less vigorous and shortened swarming period 



