Page images
PDF
EPUB

will be described later, has been termed "interior blue stain" and differs widely from the subsurface types of brown stain."

Blue stain (fig. 6) is common in the sapwood of a large number of hardwoods and softwoods, and the discoloration may appear as spots or streaks on the surface of a board or end of a log very soon after it is cut. Later, with the characteristically vigorous and rapid development of the fungus, the entire sapwood may be discolored. The telltale blue-gray color begins to show in the wood only after numerous very small threads of which the fungus is composed have reached a certain development within the cells. (Figs. 7 and 8.) When the threads, feeding on the contents of the cells and to a slight extent on

[graphic][merged small][subsumed][merged small]

FIGURE 8.-Young threads of the blue-stain fungus in the wood cells of scrub pine, showing direct penetration of the cell walls. Most of the blue-stain fungi do not penetrate the walls in a direct manner but pass through the natural openings in the walls, called pits. In the lower center one thread is passing through a bordered pit. It is the presence of such threads within the cells that gives the blue color to the wood. Enlarged about five hundred times

the cell walls, reach a certain stage in their growth, fruiting bodiescomparable in some ways to the flowering part of the higher orders of plants are produced upon the surface of the wood. (Fig. 9.) These fruiting bodies, which appear as tiny black specks upon the blued wood, when magnified are seen to resemble small black hairs or bristles swollen at the base. (Fig. 9.) From them minute spores are ejected (fig. 9) which, carried about by the wind or other agencies, germinate in new places and cause new infections. The above facts have an important bearing on the use of old blued crossers, as will be shown later.

7 Hubert, E. E., Interior Dote in Elm: Hardwood Record, 54: 18-20; 1923.

Very little work has been done to determine the effect of the bluestain fungi on the infected cell walls. Von Schrenk discusses in considerable detail the effect produced on the wood tissues by a bluestain fungus (C. pilifera) (Fr.) Wint. His drawings indicate that the fungus can readily attack and dissolve the walls between the individual cells of the medullary rays of pine wood. The inner walls of the rays are also shown to be affected, becoming thin and evidently weakened. He states: "The hyphae are apparently able to puncture the unlignified walls here and there, but they stop at that point.'

[ocr errors]
[graphic][subsumed][subsumed][subsumed][merged small][subsumed][ocr errors]

FIGURE 9.-Showing the flask-shaped fruiting body of a blue-stain fungus at A. Enlarged about one hundred times. The actual length is about five one-hundredths of an inch. At B are shown the minute spores ejected from the tip of this fruiting body and capable of germinating and starting new infections. Enlarged about eight hundred times

Münch has brought out some interesting points concerning the blue stain of coniferous woods. He states that "The bluing fungi do not attack the wood substance to any great extent but live upon the contents of the parenchyma cells." He finds that these fungi can also become parasitic in standing living trees, provided the wood contains sufficient air and little water. He found that two of these fungi were capable of killing the living cells of coniferous wood and in part those of hardwoods.

8 Von Schrenk, H., The Bluing and Red Rot of Western Yellow Pine: U. S. Dept. of Agri. B. P. I. Bul. 36: 1-35; 1903.

9 Münch, E., Die Blaufäule des Nadelholzes: Naturw, Ztschr. f. Forstu. Landw. 5: 531-573, 1907; 6: 32-47, 297-323, 1908.

Hedgcock 10 studied the fungi accompanying various stains in the wood and found several species of Ceratostomella causing blue stain in both coniferous and broadleaf hosts.

In the blued wood of the hosts examined it was found that quite frequently the fungus threads penetrated the tangential cell walls of tracheids and fibers which were not in contact or adjacent to the medullary rays. (Figs. 7 and 8, pp. 16 and 17.) In one case where the sapwood of scrub pine was found heavily blued the examination of edge-grain sections showed a single young thread penetrating three cell walls. (Fig. 8, p. 17.) In edge-grain sections of blued shingles of northern white cedar as high as 64 cell walls were observed pene

[graphic][graphic][merged small][merged small][graphic][subsumed][merged small][subsumed][merged small][merged small][merged small]

FIGURE 10.-At A and D the fungus threads of the olive black mold are seen penetrating the cell walls of persimmon wood. At B and C are shown the spores and the craterlike fruiting bodies of the above fungus enlarged about five hundred times

trated by a single thread. (Frontispiece, 1.) The threads are considerably constricted where they pass through boreholes in the cell walls, and swellings occur in the threads at the points of entrance and emergence. (Frontispiece, 2 and 4.) The young growing tip of these threads apparently is the source of the enzymes which dissolve the cell walls, since the boreholes are always of diameter corresponding to the size of the young threads. An exception to this is found in persimmon wood, where the fungus apparently is able to enlarge slightly the boreholes first formed by the young threads, since a variation in the diameter of the boreholes and amount of constriction is noticeable.

10 Hedgcock, G. G., Studies Upon Some Chromogenic Fungi Which Discolor Wood: Report Mo. Bot. Gard. 17: 59-113; 1906.

11

In a recent work on sap stains issued by the Swedish Forestry Society a belief is expressed that the threads force their way through the cell walls mainly by mechanical force and that the absence of small threads of the exact size of the boreholes in the cell walls indicate that penetration is not a direct result of enzymic action. It must be borne in mind, however, that in such cases the young threads are often colorless or nearly so and are therefore difficult to visualize unless special staining technique is used.

In the pines (fig. 7, A) and persimmon it was observed that the tracheid or fiber cell walls of the wood in close contact with certain threads are much thinner than the adjacent cell walls which had no threads in contact.

ك ك

a

EEN.

FIGURE 11.-The mycelium of the yellow-stain fungus (P. divaricatum
group) in the wood cells of oak

More often the threads search out the simple and bordered pits and pass through these, the shape of the fungous thread conforming to the shape of the openng. (Fig. 7, C, and Frontispiece, 5.) In the case of simple pits the threads must dissolve the middle layer of the cell wall in order to pass through. In the bordered pits of coniferous wood the perforated torus membrane 12 forms but a weak barrier, yet a certain amount of tissue solution is necessary to sufficiently enlarge such minute perforations as already exist.

11 Lagerberg, T., Lundberg, G., and Melin, E., Biological and Practical Researches into Bluing in Pine and Spruce Jour. Swedish For. Soc. 23: 145-272; 1927.

12 Von Schrenk, H.. The Bluing and Red Rot of Western Yellow Pine: U. S. Dept. of Agri. B. P. I. Bul. 36: 1-35; 1903.

In the less lignified medullary ray cells the effect of the fungous attack is very pronounced.13 The cell walls between the ray cells are completely decomposed, the radial walls of the ray becoming very thin and broken, so that there is less than a shell or framework of the ray left. (Fig. 7 4.) The medullary rays, in certain cases, present a seriously decomposed and evidently weakened aspect.

CULTURAL CHARACTERS

During the first few days of the development of blue-stain (Ceratostomella and Graphium sp.) threads in artificial media or on wood blocks they are observed to be colorless. Soon the mycelial growth begins to darken in color, and the cultures on malt agar, for example, turn almost black. Von Schrenk 14 states that cultures of Cera tostomella pilifera on pine blocks show the threads to be colorless during the first four to five days. At the end of this period they turn from colorless to a brown color. In from 7 to 9 days young fruiting bodies are produced, and spores are ejected from these in from 12 to 18 days. Fuil maturity is reached in 21 days. This would indicate that a new crop of spores could be expected every 18 to 21 days under conditions favorable for growth.

As we learn more about the wood-staining fungi we find new ones to add to the growing list. Recent investigations in this country and abroad have already brought many new species to light. A few of the most important stains causing loss through degrade are briefly discussed.

GRAYISH-OLIVE STAIN OF HARDWOODS

This stain was first described 15 as common on stored railroad ties cut from beech, red gum, and persimmon. It has also been found in black gum pulp logs. The stain caused by this fungus, Lasiosphaeria pezizula (fig. 10), resembles somewhat the blue stain in sap gum caused by other fungi but differs in that it is grayish olive in color instead of bluish gray. It stains both heartwood and sapwood and is usually found penetrating from 1 to 4 inches the cut ends of ties or logs. As in the case of blue stain, the presence of the fungous threads in the wood tissues is responsible for the discoloration. The majority of the hyphæ are found in and near the medullary rays, which are slightly altered by the attack. Decomposition of the ray cells is not as extensive as that produced by the blue-stain fungi. Čells in the neighborhood of the rays are usually invaded through the bordered pits and the simple pits. Penetration of the cell walls of the wood fibers is occasionally noted, and the hyphæ are always constricted when passing through the boreholes. (Fig. 10.)

The surface of the wood infected with this organism usually bears a layer of olivaceous-black mycelium, with occasional clusters of small, closely grouped fruiting structures which, when old, collapse and resemble minute craters. (Fig. 10.) The color and shape of

18 Hubert, E. E., Notes on Sap-Stain Fungi: In Phytopath. 11: 214-223; May, 1921. 14 See footnote 8.

15 Humphrey, C. J., The Decay of Ties in Storage: Proceedings American Wood Preservers' Association, 16:217-250, pls. 1-8; 1920.

« PreviousContinue »