DEVELOPMENT OF PLANTS 



233 



variation not paralleled among other plants; more than five dif- 

 ferent kinds of spores being formed by some species in their 

 life history. This is due, doubtless, to the influence of the cli- 

 mate, the spores varying with the season (spring, summer and 

 fall) and the plants upon which the fungus grows may be a 

 contributing factor to the variation, for one and the same fungus 

 may grow upon different plants, producing one or more kinds 

 of spores on each. Forms infesting different species of plants 

 are said to be heteroecious and those living upon but one species 

 are termed autoecious. 



•f 



Fig. 159. Cluster cups as seen in section of leaf of spring beauty, Clay- 

 tonia. At right one of the cups is ruptured, exposing the accidiospores. 

 Below a small cup, pycnidium, is discharging pycnidiospores that are pos- 

 sibly functionless male gametes. 



(a) The Life History of Puccinia. — Several species of this 

 genus infest wheat and illustrate the many forms that may ap- 

 pear in the life history of a rust. One phase of the life of this 

 parasite appears upon the leaves of the barberry. During May 

 and June the mycelium growing in the leaves forms roundish 

 bodies which rupture the epidermis and finally open out into 

 cups filled with chains of yellowish spores. An examination of 

 Fig. 159 shows that these spores are formed in rows at the end of 



