DAMPING OFF. 241 



thin layer next the wall becomes coarsely granular, arranged in 

 strings and is finally collected in the middle line of the antherid- 

 ium. This is known as the gonoplasm, and soon passes through 

 the fertilization tube and is emptied into the egg cell at the recep- 

 tive spot, where it disappears in the substance of the egg cell and 

 completes the act of fertilization. 



While the passage of the gonoplasm is going on it can be seen 

 that a thin wall is forming around the egg cell over the surface 

 except at the point where the fertilization tube is located. When 

 the gonoplasm has passed through, the wall becoms complete at 

 that point, and the entire wall then thickens somewhat and soon 

 becomes brown in color. The fertilized egg cell now becomes the 

 egg, or oospore. 



These phenomena in the development of the oogonia and an- 

 theridia and in the fertilization of the egg cell can be quite easily 

 followed by teasing out a small section of the diseased plant tissue 

 in water on a cover glass and arranging this for a cell culture in 

 what is known as a van Tiegham cell. This^can be placed on the 

 stage of the microscope from time to time and the development 

 traced. From such a culture made from a diseased young melon 

 seedling the following record was made. The diseased tissue was 

 teased out in water on a glass slip Monday, Jan. 28, and placed 

 in a moist chamber. The following day, Jan. 29, a profuse 

 growth of mycelium, oogonia and antheridia had taken place, the 

 mycelium extending for 2mm to 3mm out from the diseased tissue. 

 Jan. 30 a small portion of this tissue was farther teased out and 

 mounted in fresh water in a cell culture. Jan. 31 farther growth 

 had appeared and new oogonia and antheridia were developed. 

 This continued for several days in the same culture. 



On Feb. i at 12:30 p. M. as shown in fig. i, the egg cell in the 

 oogonium has formed and the antheridium curved over on one side 

 is full size but the fertilization tube has not yet formed nor has the 

 gonoplasm differentiated, the granular protoplasm being arranged 

 in a network of threads. At 3:15 P. M. of the same day as shown 

 in fig. 2 the fertilization tube is complete, the gonoplasm has 

 formed and is about to pass through the tube, while a very thin 

 wall is forming around the egg cell except -at the receptive spot. 

 At 9 P. M., fig. 3, the gonoplasm has passed through and the wall 



