THE DISEASES OF CONIFERS. 



135 



(3) P. Strohi (Kleb.) on the cortex of Pimis Strohus, P. Lam- 

 hertiana, and P. Cembra, and whicli is the secidial form of a 

 Cronartium found on species of Ribes.* 



(4) P. Pini (Willd., Kleb.), on the cortex of Pinus silvestris, 

 has nothing to do with Goleosporium Senecionis, and numerous 

 attempts have in vain been made to settle what its Uredo-spore 

 stage is, or on what host it grows ; so that here again is a pretty 

 puzzle awaiting solution by those who have the opportunity. 



Several other forms of Peridermium are known on various 

 species of Pinus. The following have hitherto been included 

 with the above under the common name P. Pini, but no one 

 will now be so bold as to retain them until further investigations 

 have decided as to their relationships. The forms in question 

 occur on the cortex of Pinus montana (Mill.), P. uncinata (Ram.), 

 P. maritima (Mill.), P. halepensis (Mill.), P. mitis (Mchx.), 

 P. Tada (L.), P. poiiderosa (Dough), P. rigida (Mill.), P. insignis 

 (Dough), P. Sabineana (Dough), P. contorta (Dough), and some 

 other American Pines ; as well as on the leaves of the Indian 

 P. longifolia (Lamb.), and of the American P. australis (Mchx.). 



The great damage done by the cortical forms of Peridermium 

 is twofold in character. In the first place the cortex and 

 cambium are killed at the spot invaded, and this injury may go 

 so far as to ring the stem or branch. Then, in the second place, 

 an abnormal formation and excretion of turpentine is excited, and 

 this soaks into the wood and renders the passage of water 

 upwards difficult or impossible. The natural consequence is the 

 perishing of the parts above the infested places, and in dry 

 summers such a result is apt to follow rapidly. 



Sections of Pine-stems, cut to 3-5 cm. thickness, thus per 

 meated with turpentine, are semi- translucent ; and, as has long 

 been known to continental foresters, the abnormally resinous 

 branches are excellent for torches, fuel, &c. 



With isolated Pines, in parks and gardens, &c., it is not 

 difficult to eradicate the disease in its early stages by judicious 

 pruning, and burning the infested parts ; far greater difficulties, 

 of course, are met with in the treatment of forests. This disease 



* Sorauer has confirmed this quite recently, finding that the spores of 

 P. Strohi develop into Cronartium Bihicola (Dietr.) on Ribes ruhrum, 

 B. nigrum, and B. aljginum (" Zeitschr. fiir Pflanzenkr.," 1891, B. i., H. 3, 

 p. 183). 



