AND FACTORS WHICH INFLUENCE THEM. 141 



genera of the Mycetozoa, which are without lime, less than half 

 show such forms. These are due to the fluidity of their plasm, 

 or to the aethalial confluences resulting therefrom. The weaker 

 the surface tension the less support it affords to the mass, and 

 the greater the depression by gravitation. Capillary effects and 

 distortion by shrinkage in drying are likewise pronounced. 



B. Globular Forms. — In these the spherical tendency of the 

 surface tension finds its clearest expression. If for a moment 

 we use the language of art rather than of science, we may say 

 that " the complete and consummate form " which is hinted at 

 by the Mycetozoa is a perfect sphere. These globular shapes 

 are exhibited by less than half the genera of the Calcarineae, the 

 lime often being an impediment. Of the remaining genera 

 about half exhibit them. 



C. Cylindrical or Vertical Forms. — In this diagram the sphere 

 is distorted by being drawn upwards, the vertical axis gaining 

 length at the expense of the horizontal circumference. The 

 natural forms which group themselves round this conventional 

 figure are significantly few and diverse. Only two genera of 

 the Calcarineae, and six of the remaining genera, exhibit them ; 

 altogether but one-sixth of the forty-eight genera of Mycetozoa. 

 In most cases the more or less cylindrical sporangia are somewhat 

 curved ; in other instances they are clavate (club-shaped) or 

 pyriform (pear-shaped), much larger at the apex than at the 

 base. These latter suggest a tendency to form a stalk. In the 

 main these upstanding forms result from lateral compression, 

 the sporangia being so crowded on the substratum that in order 

 to relieve the side pressure the plasm is forced to extend upward, 

 that being the only direction in which relief is possible. In those 

 genera in which the sporangia stand singly, the upward exten- 

 sion is due to the surface strains being modified by unequal 

 distribution of interior deposits, or varying concentrations of 

 the plasm. The definite relation between interior densities and 

 surface tensions obviously affects the shape of a sporangium 

 when from any cause such densities vary throughout the mass. 



