U8 THE LARCH DISEASE. 



surface exposed to the air e.y., the soil, the bark of old trees, or tilt- 

 thin cortex and leaves of the twigs and young trees, etc. But millions 

 of spores may go through this process of germination, and then the 

 germinal hyphse die off for want of further food-supplies ; whereas if any 

 one of these hyphse finds its way into the succulent cortex of a 

 Larch, it is nourished at the expense of the tissues, spreads into 

 the cambium, and brings about the disease referred to as the " canker 

 of the Larch." As a matter of experiment and only by experiment can 

 we arrive at such knowledge it is found that if spores of this fungus 

 germinate on the sound bark, cortex, leaf, or other part of the Larch-tree, 

 the germinal hyphae fail to effect an entrance ; if, on the other hand, 

 the spores are sown on a wound, however slight, in the cortex of the 

 tree, it is able to enter and infect the latter. 



Now the thin cortical covering of a young Larch stem or branch is 

 a dangerously tender envelope to the tissues below, and it is rapidly 

 protected later on by a rather thick coating of cork. As a matter of 

 fact the corky " periderm " begins to form, just below the epidermis, 

 before the end of the first year, and is increased every year after- 

 wards. When the tree is about twenty years old the real bark begins 

 to be formed, owing to the development of internal layers of cork. 

 Obviously the period most dangerous to the Larch is that during which 

 its cortex is still tender and its leaves succulent and delicate. In its 

 Alpine home this period is rapidly passed through ; in the lowlands of 

 Europe and in damp insular climates this period ip apt to be a dilatory 

 one, and severe checks from frosts, cold winds, periods of dull, misty, 

 "sunless" days, etc., are apt to cause the trees to suffer in all 

 kinds of ways. But such periods are not calculated to check the 

 spread of fungus-spores to any comparable extent; and so we may 

 regard these conditions as disfavouring the Larch, but not its enemy. 

 Moreover, such conditions indirectly favour the fungus, for the tender 

 shoots and young leaves of the Larch are apt to be cut by frosts, 

 bruised and torn by winds, broken by snow, and injured in various 

 ways by the inclemency of weather which would not injure them before 

 the buds opened, or after the twigs and leaves were hardened and in 

 full working order. In fact, if we could persuade our Larches to 

 remain dormant for a month later in the spring, they would escape 

 the evils of which they now run the gauntlet, as it were. 



It is during this period of dalliance in the opening of the buds and 

 pushing of the young shoots that all kinds of small wounds are made 

 by frost-cracks, bruises from hail and wind, breakages from the snow 

 and storms, and, I believe, insect-injuries, and it is into these small 

 wounds that the hyphse of the Peziza penetrate. This view is fully 

 borne out by the observations in the open that the young " cankers " 

 commonly start around the base of a dead shoot; that trees growing 

 in damp situations are particularly apt to suffer; the prevalence of 

 the disease is greatest in neighbourhoods and seasons where and win MI 

 certain insect-enemies of the Larch abound (e.y., the moth Coleophom 

 laricella, and the aphis Chermes Laricis). 



In the case of park trees, and such specimens as horticulturists are 

 dealing with, much may be done by careful pruning and paring, 

 combined with drainage and protection ; but unquestionably this Larch- 

 disease is ' a difficult matter to struggle with when once it has made 

 headway. The best " cure " is, of course, prevention i.e., plant sound 



