142 A. E. HILTON ON SPORANGIAL CHARACTERS OF MYCETOZOA 



D. Globular Forms with Stalks. — Here again, as in the sessile 

 forms B, the plasm follows to a great extent its natural tendency 

 to round off into spheres ; but not until it has deposited a stalk 

 on which it raises itself from the substratum by clinging to the 

 upper end and drawing up from the base. More than half of 

 the genera of the Calcarineae produce these forms, the lime left 

 behind in the stalks leaving the plasm at the summit more free 

 to assume a globular shape. Of the genera without lime about 

 half exhibit them, the stalks of these being chiefly of a cellulose 

 nature. 



E. Cylindrical or Vertical Forms, Stalked. — As in the case of 

 the sessile forms C, the genera presenting these are compara- 

 tively few, comprising four genera of the Calcarineae and five 

 of the other genera. In one or two instances the sporangia are 

 clustered and therefore partially moulded by lateral compres- 

 sion, but more frequently the vertical lengthening is a result of 

 the stalk continuing upwards as a columella with branching 

 capillitia nearly or quite to the summit of the sporangium. In 

 other instances where there is no columella the sporangium is 

 moulded on a frame of closely packed capillitia which afterwards 

 expands into a light mass of fibrous network. 



The feature which these stalked and lengthened forms pre- 

 eminently illustrate is the effect of inner structure upon outward 

 form. In rising sporangia the arrangement of the material 

 which forms the capillitium is primarily controlled by the plasm 

 which deposits it ; but as the process proceeds the secreted sub- 

 stances harden into a scaffolding of increasing firmness, and 

 control partially passes over from the plasm to the rigid struc- 

 tures, which largely determine the final shape of the sporangium. 

 Surface tension so far operates as to draw the plasm upwards 

 clear of the stalk, but the capillitium then arrests the climbing 

 movement, and the compromise between these two factors, 

 coupled with shrinkage effects of desiccation, lead to the charac- 

 teristic more or less cylindrical shapes. 



F. Cylindrical Forms, Stalked and Elongated. — This diagram 



