WHITE RUSTS. 133 



zoospores in a drop of water. Another series of 

 experiments was instituted by this mycologist 

 having especial reference to the parasitism of the 

 " white rust." He made numerous observations to 

 ascertain whether the spores, or the germinating 

 tubes, entered by the roots of growing plants, and 

 satisfied himself that they did not. Plants of 

 garden-cress, mustard, and shepherd's-purse had 

 their roots immersed in water impregnated with 

 zoospores. After one or two days, though the sur- 

 faces of the roots were covered with zoospores that 

 had emitted their germinating tubes in all directions^ 

 none had penetrated or showed the least tendency 

 to penetrate the epidermis. Other plants were 

 planted in flowerpots and watered at the roots with 

 water charged with zoospores, and for two days the 

 pots were left standing in the water similarly 

 charged, then the plants were removed, cultivated 

 in the ordinary manner, grew up healthy, and gave 

 no signs of the white rust. Care had been taken 

 that neither stems nor leaves should come in con- 

 tact with water containing zoospores. 



If a drop of water thus charged is placed on the 

 surface of a living leaf of the shepherd's-purse, for 

 instance, and left at rest for a few hours and ex- 

 amined minutely at the end of that period, they 

 will be found to have germinated. Let the epider- 

 mis be removed carefully and placed on a glass 

 slide and submitted to the microscope. Many 

 zoospores will be found to have produced from that 



