208 



BOTANY. 



with a remarkable motility, enabling them not only to 

 change their form, but their place also. When the proto- 

 plasm passes into a condition of rest, it forms itself into 

 small rounded masses, each of which secretes a covering of 

 cellulose about itself. This resting condition may be brought 

 about in two ways : first, through unfavorable conditions, 

 as the absence of the requisite amount of moisture ; in such 



Fig. 140. Plaamodium of Physarum leucopus (Didymium leucojnis of Link), st, 

 the more granular cuntiul part of the threads. X 350. After Sachs. 



cas.e the masses formed are larger, and irregular in size, and 

 constitute the so-called sderotium stage ; upon the return of 

 the proper conditions the sclerotia return to the soft and 

 motile condition of the original plasmodium ; the second 

 mode of formation of the resting stage takes place only 

 when the plasmodium has apparently concluded its period 

 of vegetation ; the protoplasm becomes heaped up in a com- 

 pact or even elevated mass, which then separates internally 



