K.— BOTANY. 195 



The Nutritive Requirements of the Fungi. 



The life-history of a fungus may as a rule be divided into three stages : 

 a period of vegetative growth, a conidial phase, and a phase characterised 

 by the development of the sexual apparatus. The change from the 

 vegetative condition may be influenced by food, light, temperature, 

 humidity, aeration or the encounter of mechanical obstacles ; thus 

 Sporodinia tends to form gametangia when the air is saturated with 

 moisture, while Polyporus,'^^ Lentinus ^^ and Pyronema will initiate their 

 fructifications only in the presence of light. Anyone who has grown 

 Ascomycetes in culture is accustomed to the appearance of ascocarps 

 near the edge of the dish, where free growth of the mycelium is checked, 

 and many of these fungi are also encouraged to fruit by a moderate 

 increase of temperature. It is possible that both reactions may be 

 referred to nutritive causes, since high temperature, by increasing growth, 

 uses up the available food, and a mechanical obstacle means that areas 

 of unstaled substratum can no longer be invaded. Possibly, also, a 

 nutritive cause may be assigned to the production of ascocarps of 

 Ascoholus^^ and Aspergillus'' in the presence of bacteria, and to the 

 more curious case of Lachnea abundans, communicated to me by Dr. 

 Barnes, This species fruits readily when grown on synthetic media with 

 scraps of filter paper, but not if the paper is replaced by 0-3 per cent, 

 glucose ; in contact with Penicillium glaucum, however, it fruits on the 

 latter medium. 



Most fungi are very sensitive to the presence of appropriate carbo- 

 hydrates. On substrata rich in carbohydrate Phytophthora erythroseptica 

 fails to form gametangia, but Sporodinia grandis will not produce them in 

 its absence. Similarly Eurotium herbariorum fruits best on media con- 

 taining a large percentage of cane sugar, while other fungi, like Pyronema 

 conjluens,^^ P. domesticum and Lachnea abundans show increased vegetative 

 development under similar conditions, but remain persistently sterile. 

 Some of the coprophilous sordarias fruit in culture only in contact with 

 scraps of filter paper or grass ; others are indifferent to such substances. 



The nitrogen relation is more general. The Saprolegniales tend to 

 form sexual organs in standing water, when the aquatic population is 

 high and the nitrogen content of the pool increased. Ascomycetes need 

 some source of nitrogen before gametangia can be formed ; there is 

 evidence, ^^ however, that these cannot develop till the substratum is 

 almost depleted of nitrogen compounds. The observation that heavy 

 nitrogenous manuring prevents the appearance of mushrooms and their 

 allies is in harmony with this. Nitrogen compounds are essential, but 

 must not be present in excess. 



Information with regard to other food materials is scanty, but phos- 

 phates, potassium, magnesium and calcium salts, and, in some cases, a 

 trace of iron have been found to be advantageous. The formation of 

 staling substances is often important, probably as a means of checking 

 vegetative growth ; high concentrations of sugar may have the same 

 effect, an osmotic factor being presumably involved. The evidence 

 points to specific requirements in a number of forms, and, in all, to the 

 need of appropriate food before fructifications can be produced. 



o 2 



