86 



fungus can obtain plenty of nourishment from good healthy host- 

 plants, th'te asexual method of reproduction is the only one that 

 exists. As soon as autumn begins, however, and nutriment fails, 

 the fungus begins to produce sexual organs in great abundance, 

 and it is iriteresting to observe what an immense amount of 

 material is used up in forming the protective layers of the oospore, 

 compared with that which is set aside to develop during the 

 next spring into the new plant. Roughly speaking, out of the 

 112 or more nuclei which are contained in the young oogonium 

 one or two only are set apart, together with a very small quantity of 

 protoplasm, to form the protoplasmic contents of the new cell, 

 the others, as already seen, are used up in forming the protective 

 coverings for this cell. 



Methods of Examination. 



It may be useful here to give a brief summary of the methods 

 used in the examination of the various structures mentioned in 

 this paper. 



For the examination of the Fungus in the living state, thin 

 sections of the infected plant were made by a sharp razor, and 

 mounted in water, and were tlien examined first under low and 

 next under high power. 



To obtain preparations showing the nuclei, thin sections of 

 the infected plant were stained for some time in a dilute solution 

 of hfematoxylin, and mounted in Canada balsam in the ordinary 

 way. Other preparations were stained in picronigrosin and 

 mounted in glycerine jelly. These preparations, however, although 

 they clearly showed the presence of nuclei, were not found to exhibit 

 the structure of the nucleus, or any of the minute detail in the 

 sexual organs satisfactorily, as the protoplasm itself was stained 

 too deeply, and sections could not be obtained thin enough to 

 allow the nucleus to be seen, except through a layer of protoplasm. 



Recourse was therefore had to the Cambridge ribbon-section- 

 cutting microtome. The following are some details as to the 

 methods employed. The fresh infected tissues of the Shepherd's 

 Purse were cut up into small pieces, to allow the easy penetration 

 of preservative and other fluids, and placed at once either in 

 absolute alcohol or chromic acid solution. The chromic acid 

 specimens after remaining in the solution for twenty-four hours 



