154 FUKGI. 



the narrow opening that remains in place of the papilla. In 

 normal cases the protoplasm remains united in a single mass that 

 shows a clear but very delicate outline. When it has reached 

 the front of the opening in the conidium, which is thus emptied, 

 the mass remains immovable. In P. densa it is at first of a very 

 irregular form, but assumes by degrees a regular globose shape. 

 This is deprived of a distinct membrane, the vacuoles that disap- 

 peared in the expulsion again become visible, but soon disappear 

 for a second time. The globule becomes surrounded with a 

 membrane of cellulose, and soon puts out from the point oppo- 

 site to the opening of the conidium a thick tube which grows in 

 the same manner as the germ-tube of the conidia in other 

 species. Sometimes the expulsion of the protoplasm is not com- 

 pletely accomplished ; a portion of it remaining in the membrane 

 of the conidium detaches itself from the expelled portion, and 

 while this is undergoing changes takes the form of a vesicle, 

 which is destroyed with the membrane. It is very rare that the 

 protoplasm is not evacuated, and that the conidia give out ter- 

 minal or lateral tubes in the manner that is normal to other 

 species without papillae. The germination just described does 

 not take place unless the conidia are entirely surrounded by water ; 

 it is not sufficient that they repose upon its surface. Besides, 

 there is another condition which, without being indispensable, 

 has a sensible influence on the germination of P. macrocarpa, and 

 that is the exclusion of light. To ascertain if the light or the 

 darkness had any influence, two equal sowings were placed side 

 by side, the one under a clear glass bell, the other under a 

 blackened glass bell. Repeated many times, these experiments 

 always gave the same result — germination in from four to six 

 hours in the conidia under the blackened glass ; no change in 

 those under the clear glass up to the evening. In the morning 

 germination was completed. 



The conidia of P. umbelliferarum and P. infestans* show 



an analogous structure. These bodies, if their development bo 



normal, become zoosporangia. When they are sown upon water, 



one sees at the end of some hours the protoplasm divided by 



* This is the mould which produces the potato murrain. 



