904 



Canadian Forestry Journal, January, 1917 



comes rough and cracked, the disease 

 slowly makes progress up and down, 

 or around the limb or stem, and kills 

 the branch, or the tree if it has girdled 

 the stem; or the wounded area may 

 give rise to another series of spores, 

 but at no other time of the year except 

 May or June, will the spores be seen. 

 In old pines the disease may live for 



years; young pines will succumb as 

 soon as the main stem has been 

 girdled. 



Thus far, the disease on the pines. 

 The symptoms should be carefully 

 borne in mind, and always looked for, 

 when one is in the woods in May and 

 June. 



ANOTHER STAGE OCCURS ON CURRANTS OR GOOSEBERRIES 



The fungus, as was said, produced 

 orange white dust — like a coloured 

 flour. This dust, when viewed under 

 a powerful microscope, is composed 

 of thousands of minute grains, spores 

 or, popularly, seeds of the fungus. 

 These spores, like seeds of wheat or 

 other plants, germinate in a similar 

 way. But not in soil like the latter. 

 They require living plant tissues to 

 develop. These little organisms or 

 plants, for they belong to the veget- 

 able kingdom, are parasitic and live 

 exclusively on living plant tissue, 

 somewhat as the mistletoe in Europe 

 grows upon and with its roots within 

 the living apple tree or other tree. 

 The spores produced by the white 

 pine blister rust cannot germinate on 

 the pine direct, but pass the next 

 stage of their life history on another 

 host plant. When they fall upon the 

 leaves of wild or cultivated currants 

 or gooseberries, particularly the culti- 

 vated black currant, they germinate 

 and produce on the lower surface of 

 these leaves minute little spore 

 blisters, from one to a few hundred on 

 one leaf. These blisters are filled with 

 bright orange-red spores, as small as 

 those on the pine; to the naked eye 

 they appear to be merely a reddish 

 dust, which is the early summer stage. 



This stage may appear on currants in 

 the neighborhood of the pines from 

 which the spores originally came, at 

 any time from June throughout the 

 rest of the season; though, later 

 they produce a second kind of 

 spores. The early summer spores 

 spread the disease known in this 

 stage as currant rust; from currant 

 leaf to leaf, shrub to shrub, planta- 

 tion to plantation, and thus infection 

 may travel for miles in districts 

 where either wild or cultivated host 

 plants occur. These plants are not 

 killed; premature defohation may 

 result, with consequences injurious to 

 the cultivated plants, but the para- 

 site does not kill the plant so essential 

 to the continuation of its life cycle. 

 Towards the end of the season the 

 so-called late summer spores are 

 produced. These occur on very short 

 peg-like protuberances growing from 

 the lower side of the leaves; and these 

 later spores only germinate on white 

 pines anywhere in the neighborhood. 

 This occurs in fall, and it may take 

 several seasons before a blister is 

 produced on the pine, which will give 

 rise to the pine rust stage and the 

 spores already described. This is the 

 life cycle, rounded ofT: From pine to 

 currant — and back from currant to 

 pine. 



LESSONS FROM THE LIFE HISTORY OF THE DISEASE 



This mode of life has acquainted 

 us with two very important features. 

 Without currant or gooseberry bushes 

 there can be no pine disease, that is 

 absolutely certain. If there be no 

 pines — then the currants cannot be 

 affected. Please note this point very 



carefully! If we wish to keep the 

 currants or gooseberries, the pine 

 should be destroyed: if we prefer the 

 pine— the former should be destroyed. 

 When one or other is done, this 

 disease has lost its sting. Can this 

 be done? Would we recommend, for 



