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THE MONTHLY BULLETIN. 



they produce a disease of au entirely different character and aspect from that on 

 the pine. The name white pine blister rust proper applies to the form on the pine. 

 On currants and gooseberries we speak of currant and gooseberry rust. It is from 

 this latter form that the fungus takes its technical name Vronartiiim ribicola. 



Before it was known that both forms were really nothing but the manifestation 

 of the same fungus on two different host plants, the blister rust on pines was called 

 Peridermium strobi and this name is still used when one wishes to designate that 

 particular stage of the fungus. 



To sum up, Cronariium ribicola is the name of the fungus as a whole, taken from 

 the form on currants and gooseberries, while Peridermium strobi designates only 

 the blister rust on the pine. The pine plays the role of an "alternate host" in the 

 life history of the fungus. After having passed through the stage on currants and 

 gooseberries the fungus is again able to infect the young stems of five-needle pines. 

 In this cycle the fungus develops several different types of spores. 



Fig. 79. — Older white pine tree with white pine blister rust, 

 heavy resin flow. (Photo by J. F. Collins.) 



showing 



After the infection of a young pine has taken place the fungus grows in, and feeds 

 on, the living tissues of its host until it has reached a stage in which the first type 

 of spores is formed. This appears in the shape of small, clear, honey-yellow droplets 

 exuding from minute bladdery swellings on the bark of the young stems. The drops 

 have a sweet taste and consist of very small spores, so-called pycnospores. The 

 small bladdery swellings in which the spores are formed are called pycnia (Fig. 81, 

 No. 1). Nothing is known regarding the functions of these spores. 



The pycnospores are later followed by the formation of fairly large protruding 

 white bladders containing an orange-yellow powder, which consists of a different 

 type of spores, the so-called aaciospores (Fig. 81, No. 2). The bladders in which 

 they are contained are known as aecia. They correspond to the so-called cluster 

 cups of other rust fungi. This stage is by far the most conspicuous (Fig. 77)_. 



The seciospores develop in spring, according to climate and local conditions in 

 April and May or June. Soon the bladders open and the spores drop out in form 

 of a dry powder. This dusting of seciospores continues for some time. Later the 

 production of spores ceases, the thin white membrane which forms the wall of the 

 bladder drops off and nothing is left but a discolored scar (Fig. 7S). Unless the 

 young pine is killed, the infected part continues to produce new aecia for a few years. 



