62 FUNGI INJURIOUS TO FIRS. 



The Peridermium (or ^Ecidium) Pini of authors comprises several 

 distinct species : 



(1) P. oblcmgisporium on the leaves of Pinus -sylvestris and P. 

 austriaca, the aecidial stage of Coleosporium Senecionis, 



(2) P. Cornui on the cortex of the Scots Pine, and which is the 

 aecidial stage of Cronartium Asdepiadeum. 



(3) P. Strobi on the cortex of Pinus Strobus, P. Lambertiana and 

 P. Cembra, and which is the secidial form of a Cronartium found 

 on species of Ribes.* 



(4) P. Pini, on the cortex of Pinus sylvestris, has nothing 

 to do with Coleosporium 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 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, P. maritima, P. halepensis, P. mitis, P. Tteda, P. ponderosa, 

 P. rigida, P. radiata, P. Sabiniana, P. contorta, and some other 

 American Pines ; as well as on the leaves of the Indian P. longifolia 

 and of the American P. palustris. 



The great damage done by the cortical forms of Peridermium is two- 

 fold 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 permeated with turpentine, are 

 semi-translucent ; and, as has long been known to continental foresters, 

 the abnormally resinous branches are excellent for torches, fuel, etc. 

 With isolated Pines, in parks and gardens, etc., 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 is likely to do much 

 damage in nurseries, and I think you will admit that a strong case is 

 made out in favour of the need for care and further observations as 

 regards the weeds growing in the neighbourhood of all places where Pines 

 are cultivated from seed. 



II. The Firs. I take this group in the broadest sense, including in 

 it the genera Picea (the Spruces), Abies (the Silver Firs), Tsuga (the 

 Hemlock Firs), and Pseudotsuga (the Douglas Fir). Much that has been 

 said of the Pines is also true of 'these predominantly mountain trees. I 

 shall therefore pass at once to the description of the diseases due to 

 fungi, merely remarking that those maladies traceable to unsuitable 

 climate, soil, atmosphere, etc., are much as before. 



Here, again, some of the most disastrous forms of disease are those due 



* Sorauer has confirmed this quite recently, finding that the spores of P. Strobi develop 

 into Cronartium Ribicola (Dietr.), on Ribes rubrum, A', nigrum, and fi. alpinum (" Zeitschrift 

 fiir Pflanzenkrankheiten," 1891, B. i. H. 3, p. 183). 



