. The fungal diseases of the common larch . Larches. THE LARCH CANKER 27 The most marked development of the mycehum is located in the inner cortex and outer phloem. The hyphae grow freely in the intercellular spaces (which, as shown in Chapter 1, are especially large and frequent in the outer phloem) and the resin cj'sts, and send branches through the walls into the cells, and these branches ramify and pass from cell to cell. The hyphae are usually rather small in the inter- cellular spaces, and the branches which enter cells are broader. These larger hyphae have often a wavy outline, and cont
. The fungal diseases of the common larch . Larches. THE LARCH CANKER 27 The most marked development of the mycehum is located in the inner cortex and outer phloem. The hyphae grow freely in the intercellular spaces (which, as shown in Chapter 1, are especially large and frequent in the outer phloem) and the resin cj'sts, and send branches through the walls into the cells, and these branches ramify and pass from cell to cell. The hyphae are usually rather small in the inter- cellular spaces, and the branches which enter cells are broader. These larger hyphae have often a wavy outline, and contain numerous small oil drops. As the hyphae use up the food contained in the cells of the cortex and phloem, these cells contract and leave large spaces which become tightly packed with the mycelium of the fungus, and it is from the more superficial of these close masses of hyphae that the fructifications arise. Except in cases of advanced disease, the hyphae do not grow luxuriantly in the inner phloem, cambium, or wood; this is probably due to there being few intercellular Dasyscypha in the wood J ii • £e • i of the larch. Radial spaces, and consequently msumcient section (x 630). aeration. When they do enter the wood they are at first nearly confined to the medullary ray parenchyma ; only a few branches enter the tracheides, and these do not grow freely. But as the disease advances the air-content of the wood becomes relatively much higher, and the mycelium enters the tracheides and changes the wood from the normal yellow to a reddish-brown colour. Gradually in this way the myceUum may penetrate to the centi'e of the stem and attack the heart-wood, which, having a higher air-content, provides a more suitable substratum than the sap-wood ; and, as the heart-wood increases, the fungus can flourish in it and fill many of the tracheides with. Fig. 10.—Mycelium of. Please note that these images are extracted from scanned page images that may have been digitally enhanced for
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