6i4 



tinder. These decayed tissue masses not infrequently give a cellulose 

 reaction. Such tissue is often found traversed by mycelium. Th. Hartig 

 describes the fungus as Nyctomyces candidus and A'', utilis. Rob. Hartig 

 ascribes the mycelium observed in oaks to Stereum hirsutum Willd\ In 

 other tree genera, other fungi are found which destroy the wood and which 

 are treated more thoroughly in the second volume, p. 385 ff-. 



In cross-sections of the wood structures termed "pith spots" appear as 

 isolated, sharply bounded, somewhat crescent-like, browned, decayed spots, 

 which, like passages, may be followed downward to different distances in 

 the trunk. We owe a thorough study of these to Kienitz-Gerlolf^, who 

 observed that in willows, mountain ashes and birches it is caused by the 

 feeding of an insect larva. According to a review by Karsch* Tipula 

 suspecta, Rtzb. is concerned here. This larva feeds "on the cells of the 

 cambium and the youngest wood at the time of the formation of the annual 

 ring." The passages, made by it, are closed as follows : — "the cells, break- 

 ing through the edges of the wound, grow quickly and divide with delicate 

 cross-walls. At the same time, a complete closing of the cambial ring takes 

 place and, from now on, the normal wood and normal bark are formed over 

 the wound surface, while the cavity, perfectly independent of the new 

 cambium, is closed by the increase of cells^. These injuries, due to filamen- 

 tous diptera larvae, which bore their way into the cambial zone, especially 

 at the base of the trunk and the root neck, sometimes even higher up in the 

 shaft, and in water sprouts in May and June, are primarily considered as 

 producers of pith spots or "brown chains" only in the varieties of trees 

 named. Kienitz remarks that similar structures in other trees, especially 

 conifers, do not arise from the diptera larvae above mentioned. 



In regard to the pith spots of the birch, v. Tubeuf" confirms the inves- 

 tigations of Kienitz and mentions thereby that G. Kraus explains these cell 

 aggregations as normal structures. De Bary, as was said above, speaks of 

 hypertrophies of the medullary rays and, at the first glance, one also gets 

 the impression that the pith spots are caused by a widening of the medullary 

 rays. These are seen actually to become broader before they enter the 

 aggregations of parenchyma wood and their cells take on the polyhedric, 

 thick-walled, greatly pitted appearance of the cells of the pith spot which 

 are filled at times with starch and brown tannic substances. In fact, it is 

 often found that the medullary rays, when entering the pith, are broadened 

 and unite laterally. But, supported by my "barking experiments," I con- 

 sider the newly formed, filling tissue to be a product of some cell increase 

 which can take place not only in the medullary rays but in all the tissue 



1 Hartig, Rob., Zersetzungsorscheinungen des Holzes, p. 129. 



2 Paging in the German oiiginal. 



8 Kienitz, M., Die Entstehung der Markflecke. Eot. Centralbl. 1883, Vol. XIV, 

 p. 21 ff. Here also bibliography. 



4 Bot. Jahresbericht. Jahrg. XI, Part 2, p. 518. 



5 Bot. Jahresber. 1883, Vol. I, p. 182. 



6 V. Tubeuf, Die Zellgange der Birke und anderer Laubhijlzer. Frostl. naturwiss. 

 Zeitschr. 1897, p. 314. 



