June 7, 1888] 



NATURE 



129 



mycelium awakens to renewed activity at the same time, 

 and spreads a little further upwards, downwards, and 

 sideways, its hyphae avoiding the cork-layer and travers- 

 ing the young wood and cambium below. During this 

 second spring, therefore, a still larger patch of dead tissue 

 — cortex, cambium, and young wood — is formed, and the 

 usual cork-layer describes a larger boundary. Moreover, 

 since the cambium around the, as yet, undiseased parts 

 has added a further annual ring — which of course stops 

 at the boundaries of the diseased patch — the centre of 

 the patch is yet more depressed (cf. Fig. 28). 



And so matters go on, year after year, the local injury 

 to the timber increasing, and ultimately seriously affect- 

 ing, or even bringing to an end, the life of the tree. 



At the margins of the diseased patches, as said, the 

 fungus at length sends out its fructifications. These 

 appear at first as very minute cushions of mycelium, from 

 which the cup-like bodies with an orange-coloured lining 



FlG. 30. —A, vertical section (magnified) through the dead cortex of a larch, 

 infected with the mycelium (d) of Peziza lVillkalnmii (V{\g.), which is 

 developing its fructifications (a and E). The mycelium fills up the gaps 

 in the cortex, d, with a white felt- work, it is a boss like cushion of this 

 felt-work bursting forth to become a cup-like fructification ; F, the mature 

 Peziza fructification (in section) ; c, its stalk ; r, the margins of the cup ; 

 h, the layer of spore-sacs (asci). B, four of the asci from h, very highly 

 magnified, a, hair-like barren filaments between the asci ; c, a fully- 

 developed ascus, containing the eight spores ; d, an ascus emptied of 

 spores (they have escaped through the hole at the apex) ; b x a young 

 ascus in which the spores are not yet formed : to the left below is a small 

 one still younger. (After Hartig and Willkomm.) 



arise : the structure of this fructification is best seen from 

 the illustration (Fig. 30, A). The orange-red lining (h) is 

 really composed of innumerable minute tubular sacs, each of 

 which is termed an ascus, and contains eight small spores : 

 as seen in the figure (Fig. 30, B), these asci stand upright 

 like the pile of velvet lining the cup. They are formed in 

 enormous numbers, and go on ripening and scattering the 

 spores day after day. There are many interesting details 

 connected with the development and structure of these 

 fructifications and spores ; but we may pass over these 

 particulars here, the chief point for the moment being 

 that very large numbers of the minute spores are formed, 

 and scattered by the wind, rain, animals, &c. Moreover, 

 as already stated, it has been shown by experiments that 

 the spores will infect the stem of the larch if they are 

 introduced into a wound ; but it is important to notice 

 that the fungus cannot penetrate the sound cortex. 



It now remains for us to see if, in the natural course of 



events, infection of the larch can take place to any great 

 extent ; for, unless this is the case, we cannot reconcile 

 the above peculiarities of the fungus with the prevalence 

 of the disease. 



It must be borne in mind that the larch is an Alpine 

 tree, growing naturally at an elevation of from about 3000 

 to 6000 feet above sea-level, and even more. In its native 

 heights, both the larch-disease and Peziza Willkommii 

 occur associated as we have described them, but the 

 malady does not become epidemic, as it has done in the 

 valleys and plains of Europe. 



Several insect-enemies of the larch are known, some 

 of which feed on the buds, and others on the leaves, 

 &c. : it is not impossible that insect-wounds may serve 

 occasionally as points of entry for the fungus. 



But attention should be directed to the remark made 

 when describing the symptoms of the disease — namely, 

 that a dead branch often springs from near the centre ot 

 the patch. Now it is a well-known fact in the hill-forests 

 of Switzerland, Germany, Austria, &c, that heavy falls 

 of snow often load the branches until they bend down to 

 the ground, and the bark in the upper angle where the 

 branch joins the stem is ruptured ; similar cracks are also 

 caused by the bending down of the branches under the 

 weight of water condensed from mists, &c. If a spore 

 alighted near such a place, the rain would wash it into 

 the crevice, and it would germinate in the moisture 

 always apt to accumulate there. This certainly accounts 

 very completely for the situation of the dead branch, 

 which of course would at once suffer from the mycelium. 

 Another way in which such wounds as would give access 

 to the parasite might arise, is from the blows of hailstones 

 on the still young and tender cortex. 



But probably the most common source of the crevices 

 or wounds by which the fungus gains an entry is frost ; 

 and to understand this we must say a few words as to 

 what is known of the larch at home in its native Alps. 



It is well known, since Hartig drew attention to the fact, 

 that in the high regions of the Alps the trees begin to 

 put forth their shoots very late : the larch in the lowlands 

 of Germany and the British Isles often begins to shoot at 

 the end of March or beginning of April, whereas in the 

 mountains it may be devoid of leaves in May. This is 

 because the transition from winter to spring is very sud- 

 den on high slopes, whereas in the lowlands and valleys 

 it may be very gradual. The consequence is that in the 

 Alps, when the buds once begin to open they do this 

 rapidly and vigorously, and the tender leaves and shoots 

 are quickly formed and beyond the reach of those late 

 spring frosts which do so much damage in our country : 

 in the lowlands, on the contrary, the leaves slowly deve- 

 lop at a time when late frosts are very apt to recur at 

 night, and they are for several weeks exposed to this 

 danger ; and if a sharp frost does come, the chances are 

 that not only will the first output of tender leaves be 

 killed off, but the whole shoot suffers, and frost-wounds 

 are formed in the young cortex. 



Another point comes into consideration also. In warm 

 damp valleys the whole tree is apt to be more watery, 

 and it is well known that the soft tissues, like the cortex, 

 suffer more from frost when filled with watery sap, than 

 do harder, drier, more matured ones. It has been shown, 

 according to Sorauer, that dead patches, exactly like those 

 which characterize the larch-disease in its early stages, 

 can be artificially produced by exposing the stem to 

 temperatures below zero, so as to freeze the water in the 

 cells. 



Given the above conditions for producing frost-wounds, 

 then, and the presence of spores of Peziza Willkommii, 

 there is no difficulty in explaining the well-known 

 phenomena of the larch-disease. 



But Hartig has brought to light some other facts of 

 great importance in considering this admittedly com- 

 plex question. We have already stated that the Peziza 



