156 MANUAL OF TREE DISEASES 



In all these diseases the general symptom is the production 

 from the mider surface of the needles in early summer of white 

 bladdery pustules or blisters. Although found rather conmionly 

 throughout the range of the firs, none of these diseases is known 

 to cause any great damage. A yellowing of the foliage and 

 defoliation may occur at times. The different species of rust- 

 fungi causing these diseases require certain other kinds of 

 plants on which to complete their life history. In all the species 

 the spores (aeciospores) developed in the white blisters on the 

 fir cause the infection of the other host plant if it is in the close 

 vicinity. On this second host urediniospores are formed in 

 small reddish or yellowish spots in midsummer and in the 

 autumn the teliospores develop either within the epidermal cells 

 or on the outside of the leaf or stem. The teliospores over- 

 winter and germinate in the spring, producing basidiospores 

 which when blown to the fir infect the young needles. 



Fern rust. 



The most common and generally prevalent of the blister- 

 rust fungi of fir needles have alternate stages on species of ferns 

 and belong to the genus of fungi known as Uredinopsis. The 

 blister-stage on the fir needles is known as Peridermium halsa- 

 meura Peck and P. psevdo-bcUsaTneum (D. and H.) Arthur and 

 Kern. These rusts occur on balsam fir in the northeastern 

 states and on Alpine, grand and noble fir in the Northwest. 



Recent investigations have shown that these blister-rusts are 

 the alternate stages of five previously recognized species of 

 Uredinopsis on ferns as follows : — 



U. osmundoB Magn. on species of Osmunda; 



U. mirabilis (Peck) Magn. on species of Lorinseria and Onoclea; 



JJ. struthiopleridis Stromer on species of Anchistea and Matteuccia ; 



U. phegopteridis Arthur on species of Phegopteris ; 



U. Atkinsonii Magn. on species of Asplenium and Dryopteris. 



These rusts are not distinguishable from one another in the 

 aecial stage on the fir needles, and further investigation may 



