144 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



e.g., the soil, the bark of old trees, or the thm cortex and leaves 

 of the twigs and young trees, &c. 



But millions of spores may go through this process of ger- 

 mination, 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 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 hyphse 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 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 afterwards. When the tree is about twenty 

 years old the real bark begins to be formed, owing to the develop- 

 ment 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 is apt to be a dilatory one, and severe 

 checks from frosts, cold winds, periods of dull, misty, " sunless " 

 days, &c.,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 



