58 A. R. HILTON ON THE LIFE-PHASES OF MYCETOZOA. 



foraging of the creeping plasmodium, and continues until a point 

 is reached at which congestion brings the process to a standstill. 

 Then, in the spore-forming stage, the action is reversed, and the 

 plasm is relieved by the excretion of its impedimenta, which 

 are deposited as substrata, stalks, capillitia, sporangium walls, or 

 spore-shells. In the matured spores the purified plasm, in a 

 condition of renewed vigour, waits in readiness to resume the 

 exercise of its motile powers as soon as the necessary conditions 

 afford opportunity. 



In the meantime, this sporangial or dry phase of the life- 

 cycle possesses features of peculiar interest. Bear in mind 

 that practically the whole of the purified plasmodium passes 

 into the spores. In the process a plasmodium may produce 

 some hundreds of symmetrical sporangia, or fewer and larger 

 ones of irregular shape, known as plasmodiocarps, or single, 

 cushion-like forms, aethalia, which may be several inches across. 

 In any case, however, the dust-like spores are so minute that 

 in a small sporangium the number is probably not less than 

 fifty thousand, while in the larger forms they may exceed a 

 billion. All the spores of Mycetozoa are spherical or nearly so, 

 and those in a sporangium are usually of such uniform dimen- 

 sions that the size of them is a valuable guide in determining 

 the species. Each spore contains a tiny speck of plasm, with a 

 single nucleus, in a more or less central position. 



This means that the resting-stage at which the plasm arrives 

 when spore- formation is complete is a condition of equilibiium. 

 The multiplication of nuclei, which begins with the division of 

 the swarm-spores, increases enormously in a growing plasmodium ; 

 and there is a further multiplication of nuclei in the purer plasm 

 immediately before the spores are formed. So far, however, the 

 plasm has been in a state of disturbed equilibrium, the stress of 

 which largely explains its restlessness. The lively movements of 

 .swarm-spores, the reversing currents w^iich stream through the 

 veins of the plasmodium, and pulsations observable in imma- 

 ture sporangia, are vivid expressions, on a larger scale, of the 

 oscillations which underlie them. The phase of actual spore- 

 formation is essentially the regaining, for a time, of equilibrium 

 which has been lost ; and the mass of uniform spores into which 

 the whole of the purified plasm has passed is the geometrical 

 expression of this balanced condition. 



