![Thumbnail: [Volume 82, 1954-55 page 117]](/journals/rsnz/images/rsnz_82/thumbnails/rsnz_82_01_0142_0117_ac_02.gif)
Isolation of the Fungus
Twigs 1–2 cms. long, covered with mycelium were washed for 8 hours in a suitable laboratory washing device. Surface sterilisation with the usual agents was found to be harmful to the fungus. After washing, one or two twigs were placed in a sterile test-tube with 3–5 ccs. of sterile water, and ground with a sterile rod. The resulting suspension of hyphal fragments was used to make dilution plates. It was found that the fungus could be isolated most readily on a decoction of L. scoparium twigs which were heavily infected with coccids and therefore contained a large quantity of honey-dew. The twigs were soaked in hot water for several hours. The resultant liquid was turbid with fragments of hyphae, and had a sweetish smell. This liquid was filtered, the filtrate solidified with 1.5% agar and sterilized at 101b pressure for 20 minutes. Dilution plates poured with this medium were examined microscopically with a low-power objective after incubation for 3 days at 24° C. Germinating hyphae well-separated from contaminants were transferred to tubes containing the same medium.
Several agar media were employed to determine the colony characteristics of the fungus. Czapek-Dox medium, made according to Thom and Raper (1945), was used with various carbohydrates—i.e., sucrose, dextrose, maltose, dextrin. Saboraud's Agar, Malt Agar and Potato Dextrose Agar according to Ainsworth and Bisby (1945) were also used.
Maximum growth was obtained on Czapek-Dox Agar with maltose of pH 6.8 at 24° C.
Aerial hyphae were produced on Prune Agar, Saboraud's Agar, Difco Lima Bean Agar and Czapek-Dox Agar. Microspores were produced abundantly on Czapek-Dox Maltose Agar, Honey Agar (5% honey, 2% agar), Malt Agar and Potato Dextrose Agar. On these media the colonies assumed a white slimy appearance due to the numerous microspores produced.
Microtome sections of cultures growing on agar were prepared in order to examine the colony structure. The colonies were found to consist of closely packed hyphae composed of doliform cells. Microsporangia (Fig. 2) were found scattered irregularly throughout the colony; their size and shape was irregular but tended from spherical to obclavate in form. The Avails are composed of two layers of isodiametric cells. A circular ostiole appears at the apex through which the microspores are exuded in large numbers embedded in a mucilaginous fluid. The microspores are oval in shape and thin-walled. They are usually without septa, but a few have one septum. Length varies from 2·7μ–5.5μ. (mean 4.0μ). and breadth 2.5μ–3.3μ (mean 2.8μ). No other spores were produced by the fungus in culture.
![Thumbnail: [Volume 82, 1954-55 page 118]](/journals/rsnz/images/rsnz_82/thumbnails/rsnz_82_01_0143_0118_ac_02.gif)
The description and measurements given below were made from fresh material mounted in glycerine jelly.
The hyphae (Fig. 3) were clear dark-brown in colour, darker in the older portions; and lighter towards the apices. Newly formed cells were almost hyaline with a greenish tinge; mature cells were doliform and much constricted at the septa while young hyaline cells showed no constriction at the septa. The cell wall was unsculptured, branches arising from any part of the hypha and in any plane. Numerous globules which stained with Sudan IV were present in the older cells. The cell measurements were 4.1μ–14μ long by 4.1μ by 15μ wide.
The flask-shaped pycnidia (Fig. 4) were borne partly imbedded in the mycelium, singly or in groups of two or three, both on the stems and leaves. The walls were made up of 3–5 layers of closely appressed cells. Pycnidia were observed at all seasons. The size was variable, 112μ–260μ in length, 45μ–100μ wide at the base and 19μ–32μ. wide at the neck. The pycnospores were fusiform, and often slightly curved, 21μ–36μ, by 3μ—4μ, golden-brown in colour and with usually 9 septa though these varied from 7 to 13.
Asci were produced in perithecia (Fig. 3) which are usually spherical, slightly flattened at the apex. The walls consisted of thick-walled cells of variable size. The assocarps measured 70μ–150μ long by 55μ–90μ wide.
Asci were obclavate and thin-walled. They contained 8 ascospores which were clavate, thick-walled and dark green-brown in colour. The number of septa varied between 2 and 5; the majority were found to have 3 septa. They measured 20μ–28μ long by 6μ–11μ wide.
The fungus described above agrees in all aspects, other than the breadth of the pycnospores, with the amended description of Capnodium walteri Sacc., given by Fraser (1935). Fraser gives the width of the pycnospores as 7μ-9μ: in my observations they were 3μ-4μ. However in an earlier description (Fisher, 1932) the average width is given as 5.5μ; it would not appear that this slight difference is great enough to warrant a new species.