138 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



and Abies halsamea (Mill.), and it will probably turn out to be 

 more widely spread than has been hitherto suspected. 



The Silver Firs suffer from a number of other Uredines, of 

 which Cceoma Abietis i:)ectinat(B is a form reminding us, by its 

 habit and behaviour, of Galyiotospora Gmppertiaiia. 



The Spruces (Picea) are also apt to suffer much from Uredinese, 

 of which the genus Chrysomyxa is one of the most important. 

 Several species of this fungus do considerable damage to the 

 leaves, by causing them to fall prematurely — e.g., C. Abietis,^ 

 C. Bhododendri and C. Ledi — the former being autoecious, and 

 only occurring in the Teleuto- spore stage, so far as is known ; the 

 two latter being heteroecious, the ^cidia developing on the leaves 

 of the Spruce, and the Uredo-forms on the leaves of Bhodo- 

 dendron ferrugineum and B. hirsutum, and on those of Ledum 

 'palustre. Farlow says that C. Abietis occurs on Tsuga cana- 

 densis (Carr.), which suggests the probability that this form 

 again is more widely spread than has been supposed hitherto. 

 Miinter states that Ficea alba (Lk.) is not affected by this 

 disease. I quote from Sorauer,t and cannot speak from my 

 own knowledge ; but Farlow does not give this fungus on P. alba. 



Spruces (and to a less extent Silver Firs and Pines) are often 

 affected with a disease caused by an Ascomycete (Nectria 

 Cucurbitula), the hyph^e of which find their way through small 

 wounds in the cortex, into the sieve-tubes, &c., of the phloem, 

 and set up a struggle for existence, which is very interesting to 

 the biologist, though it may be viewed with different feehngs by 

 the horticulturist. It appears that so long as the Fir is doing 

 well, the parasite is confined to the resting parts of the phloem, 

 and cannot make its way into the active cambial region, tlie 

 living cells of which go on dividing and growing quite normally ; 

 if the attacked branch is particularly vigorous, the formation of 

 a layer of cork may be accomplished, which cuts off all the 

 diseased tissues, which then dry up and are thrown off. 



It is a particularly instructive fact, however, that if the season 

 is one unfavourable to the rapid and vigorous development of the 

 cambium, or the tree generally, or if conditions exist in the soil 

 or atmosphere which retard the vegetative activity of the cells, 



* Beautiful figures of this are to be found in Willkomm, " Die mikro- 

 skopischen Feinde des Waldes," 1867, Taf. IX. The text is now chiefly 

 of historical interest. 



t " Pflanzenkrankheiten," 2nd edit. 1886, vol. ii., p. 248 



