SECTIONAL TRANSACTIONS.—K. 485 
Dr. Mary J. F. Grecor.—-Heterothallism in Ceratostomella pluriannulata, 
Hedgcock. 
This species is characterised by the extremely long neck of the perithecium which 
bears, in addition to the usual terminal fringe of cilia, accessory fringes lower down 
the neck. A conidial stage of the Cladosporium type occurs in the life-cycle, but no 
Graphium form. 
The fungus was isolated from elm wood and numerous series of monoascospore 
cultures were made ; it was found to be heterothallic, the + and — strains being 
produced in about equal proportions. Female organs are formed on both mycelia, 
but no male organs. When the two strains are grown in association, these female 
organs develop into normal perithecia containing spores, but when one mycelium is 
present alone, they undergo only a partial development, giving rise to small spherical 
*bulbils.” Occasionally a few bulbiis may continue growth and form dwarf perithecia, 
which, however, never contain spores. 
Numerous experiments have been carried out in an attempt to induce a more 
abundant production of dwarf fructifications and to stimulate these to develop spores 
in the absence of the second strain of the fungus. The experiments include the 
addition of various chemicals to the nutrient medium on which the cultures were 
grown, the addition of a filtered watery extract of the other mycelium, the action 
of heat, extreme cold and ultra-violet rays. These methods, however, have all failed 
to produce the desired result, and it appears probable that mature perithecia can only 
be formed by the interaction of the + and — strains. 
Prof. O. V. DarsisHire.—Observations on the Occurrence of Air Pores in 
Lnchens. 
Little is known of the detailed anatomy of lichens, and still less of their physiology. 
In their general anatomical differentiation lichens resemble somewhat the higher 
green land plants, but the lichen organism differs markedly from the green land plant 
in the varying development and the unequal and irregular distribution of air pores, 
by which the air in the loosely plectenchymatous medullary layers might be connected 
with the outside air. In some foliaceous and fruticulose lichens the air passages of 
the medulla seem to be completely cut off from the surrounding air. In others 
practically the whole underside of the foliaceous thallus is open; in still others we 
find well-defined cyphelle of definite size and shape, and in a few, special pores of 
smaller size. In Peltigera pretextata these resemble stomata in appearance. The air 
pore is the response of the fungus to the control by the lichen gonidia. The alge 
must be kept from drying up. This control results in the fungus of the corticate 
lichens always keeping the alge well covered. Transpiration in lichens is always 
slow despite the absence of any cuticle. Air pores are generally found on the lower 
side of the thallus, and thus transpiration through them is kept under. The size 
and structure of the air pore is a compromise between the general requirements of 
the alge and the average danger of their desiccation. The method of development 
of the pores in Peltigera pretextata may possibly serve as an indication of the way in 
which stomata originated in the very earliest ancestors of the green land plants of 
to-day. 
Gen. the Rt. Hon. J. C. Smuts, P.C., F.R.S.—Observations on a Botanical 
Tour in Tanganyika. 
AFTERNOON. 
Dr. F. M, L. Suerrrerp.—Some Cytological Aspects of Virus Diseases in 
Plants. 
Dr. J. Catpwetu.—Investigations on Some Physiological Aspects of Virus 
Diseases in Plants. 
For the physiological investigations discussed in this paper one virus Aucuba 
Mosaic of Tomato in its host Tomato (Lycopersicwm esculentum) was largely used. 
This virus wa chosen because it is easily transmitted by juice inoculation, gives 
consistently well-marked and definite symptoms and remains active in vitro over 
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