AND INHERITANCE IN PEDIASTRUM. 439 



of the same mother colony just ready to swarm. Empty cells of the same 

 mother colony are also shown. The cells of the two daughter colonies already 

 four-lobed and looking almost as if they were dividing in their short axes. 

 X about 1,050. 



Fig. 16. The same group a few minutes later less highly magnified and 

 showing seven daughter colonies and part of an eighth all more or less out of 

 focus. The swarmspores have just escaped from the right-hand mother cell 

 of the two shown in Fig. 15 and appear as a rounded cloud partly beneath 

 the left-hand mother cell. They are swarming vigorously and are also a 

 little out of focus. X about 500. 



Fig. 17. The same group a few minutes later than the stage shown in 

 Fig. 16. The swarmspores have come to rest in the newly formed colony and 

 the rounded outline of the colony and its concentric series of cells can be 

 made out though it is somewhat out of focus in this figure also. X about 500. 



Plate VI. 



Figs 18, 19 and 20. Young daughter colonies still enclosed in the vesicles 

 in which they escape from the mother cell. The vesicles are very transparent 

 and hard to bring out in the photographs. In Figs. 18 and 20 I have traced 

 their outlines over with dilute India ink; in Fig. 19 they are left as they ap- 

 peared in the print and while they are very faint they can be seen and it is 

 clear that in shape they still maintain the outlines of the mother cell even to 

 the slight projections representing the larger pair of spines. The walls of 

 the mother cells, also shown, enable us to compare the size of mother cell, 

 vesicle and young colony. The tendency of the young colony to conform 

 more or less to the oblong shape of the vesicle is obvious, but the edge view 

 of a colony in Fig. 29 shows that in these cases at least this tendency has not 

 prevented the formation of the plate of a single layer of cells though the 

 space relations in the vesicle would favor the formation of two or three 

 layered groups such as are shown in Fig. 23. X about 1,050. 



Fig. 21. Two young daughter colonies, one with sixteen, the other with 

 thirty-two cells, both being the offspring of a thirty-two-celled mother colony. 

 The young colonies are of the same age, but the cells of the sixteen-celled 

 colony are proportionally larger. X about 500. 



Fig. 22. A mother colony and six young daughter colonies, all of which 

 show more or less the influence of the oblong mother cell vesicle on their 

 shape. X about 150. 



Fig. 23. Ten extremely young daughter colonies, all from the same 

 mother colony. Reproduction occurred in this case after the mother colony 

 had been sealed up as described for about eighteen hours and the free swim- 

 ming movements of the swarmspores were almost entirely suppressed. The 

 colonies are two or more layers thick and the interrelations of the cells are 

 entirely abnormal and yet the cells themselves have taken on the four-lobed 

 form typical of the species. X about 150. 



Fig. 24. Four young colonies from the same mother colony, illustrating 

 still further, as do the preceding figures 15 to 23, the extreme range of fluctu- 

 ating variation in cell arrangement which can be found in the offspring of 

 a single mother colony, while in all the type of cell form remains quite con- 

 stant. X about 400, 



