234 



LIFE HISTORY OF A RUST 



hyphae and surrounded by a layer of rather thick-walled hyphae. 

 This stage of the rust is known as the cluster cup or aecial stage 

 and the spores are called aeciospores. Often smaller spore-bear- 

 ing cups, known as pycnia (sing, pycnium), are associated with 

 this phase of the fungus. These small spores, while capable of 

 germinating, do not appear to enter into the life history of the 

 fungus by producing a new parasite. They have been looked 

 upon as male gametes that originally effected fertilization in a 

 female organ from which developed the spore-bearing cluster cup, 

 the process being similar to that noted in the Red Algae. On 

 the other hand they are regarded by some authorities as spores 

 that have lost their power to germinate and so breed the fungus 

 asexually. The process of spore formation in the cluster cup, 



Fig. 159^. Spore formation in a cluster cup: i, appearance of the hyphae 

 in a young cup. 2, one of the cells from Fig. i, after it has divided into 

 the sferile cell and the large basal cell. 3, early stage in the fusion of the 

 basal cells of two adjacent hyphae. 4, the two nuclei of the fused cells have 

 divided and two of them are passing to the base of the cells and two into the 

 fused region of the cells. 5, the upper portion of the fused area is cut off, 

 forming the spore mother cell. This cell will divide once, forming a spore 

 and a small sterile cell. 6, a chain of spores and sterile cells is being formed 

 as noted in 5. — After Christman. 



