THE FUNGI WHICH CAUSE PLANT DISEASE 351 



I (=Peridermium strobi). ^cia caulicolous, causing fusiform 

 swellings of the stem, rounded to elongate; peridium inflated, rup- 

 turing at sides, thick, membranous. Spores ellipsoid to ovoid, 

 18-20 X 22-23 fi, wall colorless, coarsely verrucose except on 

 elongate smooth spot, 2-2.5 n thick, on smooth spot 3-3.5 n 

 thick. 



II. Uredinia hypophyllous, thickly scattered in groups, round, 

 pustular, 0.1-0.3 mm., at first bright yellow; peridia delicate. 



Fio. 255. — Cronartium. A, urediaium; B, telium. 

 After Tubeuf. 



Spores ellipsoid to obovate, 14-22 x 19-3.5 /t, wall colorless, 

 2-3 n thick, sparsely and sharply echinulate. 



III. Telial columns hypophyllous, cylindrical, 125-150 fi thick, 

 up to 2 mm. long, curved, bright orange-yellow, becoming brown- 

 ish; spores oblong or cylindrical, 8-12 x 30-60 n; wall nearly 

 colorless, smooth, rather thick, 2-3 /t. 



Hetercecious 0, I, on white pine, Pinus cembra and several 

 other 5-leaved species; II and III on currant and gooseberry and 

 several other species of Ribes. 



The telial stage was first noted in Geneva, N. Y., in 1906.^*^ 

 The rust is now known in some nine states. It has been known in 

 Europe since 1854. Its effects are most serious in its aecial stag6, 

 though the telial stage is very abundant and conspicuous. The 

 generic connections of the forms was proved by Klebahn in 1888 

 by inoculations. 



The mycelium is doubtfully perennial in Ribes and certainly is 

 so in the bark of the pine. 



