DISEASES. 53 



In tlie Scotch Pine a great amount of resin is itroduccd, and this, acciinuihitinf,' in tlie lower 

 part of tlie stem, i)robably acts as a barrier to the growth of the mycelium npwanl. In the White 

 Pine the fungus extends much farther in the trunk. 



PI. XII, 7, represents a stump of White Pine that has been attacked hy I'olypotKK amiosiis. 

 The heart is surrounded by decayed M'ood and spots tilled with masses of resin. PL XII, 9, 

 represents parts of adjacent wood elements of Xorway Spruce after they have been acted upon 

 by the fungus; the mycelium hyphai and spores, highly maguitied, are represented in JO of the 

 same plate. 



(3) Coh'osporium sciiccioiiis Pers. — This fungus, under the name of "pine blister." infests 

 various species of pines, growing in the a'cidium stage on both leaves and bark, and sometimes 

 proving very destructive. When growing on the leaves it affects but little the vitality of the tree, 

 but is highly injurious when the bark is the place of attack. It penetrates the bark, apparently 

 through wounds occasioned by insects, woodpeckers, or other agencies, and its mycelium spreads 

 through the cortical parenchyma and bast, and into the wood to the depth of several inches, 

 passing through the medullary rays. 



Under its influence the starch and other cell contents disappear and a resinous substance 

 collects in their stead, a mass of dead tissue soon taking the place of the living cells. This change 

 of the cell contents results in a great accumulation of resin, which often exudes in large quantities 

 from the diseased parts of the tree. 



The mycelium is perennial, extending itself through the stem from year to year, particularly 

 in a longitudinal direction. Where it is present the growth of the stem is prevented and the 

 formative materials are diverted to the opposite side of the stem, causing there a greatly stimulated 

 and abnormal growth. The death of the leader often results, especially in dry summers, for the 

 reason that the wood, thus choked with resin, is unable to supply it with sufticient water. 



The researches of Wolf lead to the conclusion that this parasite of the pine lives in the form 

 known as Goleonjwriuvi senecioniii on various species of Senecio, and that it is communicated to 

 pine shoots from them. He proposes the extermination of these hosts as a preventive measure. 

 Later investigations of Kleebahn go to show that a blister rust which he observed badly aftecting 

 the bark of rinits strobus, in the neighborhood of Bremen, is caused by a closely related parasite 

 form which he names Peridermium strobi, and considers to be the ;ecidium stage of Cronartium 

 ribicola. 



All these fungi have probably caused far more destruction of timber than casual observation 

 would indicate, but the limited extent to which artificial cultivation of forests has thus far been 

 carried on in this country gives comparatively few exact data regarding them. The facts, as above 

 stated, have therefore been drawn largely from the works of Ilartig and other European authorities. 

 With increasing cultivation of timber and probable increase of such diseases, their investigation 

 and the employment of protective measures must necessarily receive far more attention. 



Several diseases attributable to the action of fungi, but as yet imperfectly investigated, are of 

 frequent occurrence in this country. One of these, known as '-damping off,"' characterized by the 

 sudden decay of seedlings at the surface of the ground, is common in nurseries, and attacks yonng 

 plants of different kinds, the White Pine among them. 



The disease is most prevalent in plants growing in a damp soil in a warm, moist atmosphere. 

 As observed in the Ann Arbor (Michigan) greenhouses for several years in various plants propa- 

 gated from slips, the disease appears a few days after the slijjs are set, giving the lower part of 

 the stem a wet, unhealthy appearance, which extends to the lower leaves, particularly where these 

 touch the sand in which they are growing. Upon taking up the specimens, the parts affected are 

 found to be in the early stages of decay, and penetrated throughout, even in the interior of the 

 epidermal appendages, by the branching filaments of a fungus. The fungus appears to live in the 

 sand in which the plants are jiropagated, and to run in it from one to another, resulting often in 

 the rapid destruction of the plants in the bed. 



"Damping off" is due to the action of several different parasitic organisms, of which the 

 pottingbed fungus, I'l/thiiim ile Jxinjaniun Hesse, is one of the most common, though a number of 

 other species have been shown to be capable of producing the disease. The relief measures 

 recommended by those who have studied the disease are the use of fresh soil free from decaviug 



