1304 



FUNGI 



FUNGICIDES 



1609. Germinating spores. 



a, Conidium of late blight fungua germi- 

 nating in a drop of water by swarm-spores; 

 a', swarm-spore germinating by germ-tube; 

 b, ascospore of apple-scab fungus sending 

 its gerra-tube into the cuticle 6' of the 

 young apple. 



sufficient moisture, and given the proper tempera- 

 ture, they usually will germinate quickly, either send- 

 ing out a sprout-like germ-tube (Fig. 1609, 6) which 

 on iinding sufficient nourishment grows into myce- 

 lium, or the protoplasmic contents of the spore-cell 

 may escape through an opening formed in the cell-wall, 



as one or more 

 actively s w i m- 

 ming and naked 

 protoplasmic 

 masses, called 

 swarm - spores 

 (Fig. 1609, a). 

 These swarm- 

 spores swim 

 about in the 

 water for a time, 

 (usually less 

 than an hour), 

 then invest 

 themselves with 

 a cell-wall, and 

 germinate with 

 a germ-tube as 

 above described 

 (Fig. 1609, a'). 

 This latter is the method of germination of the potato- 

 blight fungus, Phytophthora infestans. — A fungus often 

 produces two kinds of spores, the vegetative spores, 

 conidia (Fig. 1608, j), produced usually in great num- 

 bers and repeatedly during the season for the purpose 

 of multiplying the form, and the sexual, or resting- 

 spores (Fig. 1608, a, b, c, d, k), adapted primarily to 

 carry the fungus through periods unfavorable to growth, 

 as dry seasons, winter and the like. Either form may, 

 however, function as the other. They are disseminated 

 by wind, water, insects, or by man himself. 



Because of their lack of chlorophyll, fungi cannot 

 assimilate their carbon directly from the carbon- 

 dioxid of the air as can the green plants. They must 

 make use of the food substances already manufactured 

 or elaborated by other plants or animals. With respect 

 to the nature of the substratum from which fungi 

 obtain their food-supply, the}' are of two general 

 types, saprophytes, those that can feed and develop 

 on non-living organic substances (chiefly dead parts of 

 plants and animals); and parasites, those that may 

 grow upon and take food from living organisms. A 

 true or obligate saprophyte can feed only upon non- 

 living organic substances. There are great numbers 

 of such species, attacking dead and fallen trees, stems 

 and leaves of plants or the dead bodies of animals, 

 infesting dung and other debris, breaking up the com- 

 plex organic substances into simpler form, and deriving 

 therefrom the food and energy for their development. 

 Most mushrooms, toadstools, molds and the hke, 

 are obligate saprophytes, playing the role of disin- 

 tegrators in the 

 ever-changing 

 cycle of nature. 

 An obligate para- 

 site, on the other 

 hand is, in nature 

 at least, compelled 

 to derive its nu- 

 trition through 

 direct attack on 

 the living tissues 

 of other plants or 

 of animals. Of 

 such fungi, the 

 rust- and smut- 

 pi oducing para- 

 sites, the leaf-curl 



fungus of the 1610. Colonies of the rust fungus on 



peach, and the the leaf of a hollyhock. 



potato-blight organism are good examples. Between 

 these extremes are to be found very many forms 

 which, during a part of their active development, 

 live as parasites, and during the remainder as sapro- 

 ph3'tes. The apple-scab fungus is a good example. It 

 passes the summer as an active parasite upon the 

 leaves and fruit of the apple, but in the autumn and 

 spring continues its growth and development in the 

 fallen leaves, producing the sexually formed ascospores 

 which in the spring infect the next crop. Other forms, 

 which usually lead a saprophytic existence on the 

 dead and fallen parts of plants, may, under special 

 conditions, take on a parasitic habit. A good example 

 is a common saprophyte, a species of Botrytis, com- 

 mon in greenhouses. When there is an excess of moist- 

 ure or the plants are in any way weakened, this fungus 

 finds it easy to pass from a saprophytic Ufe on the dead 

 leaves, to that of active and destructive parasitism on 

 the living leaves. It is sometimes destructive to let- 

 tuce. Fungi are in general favored by abundance of 

 moisture. For this reason in a wet season mushrooms 

 appear in great profusion, and epidemics of plant- 

 disease-producing fungi often 

 occur over wide areas, caus- 

 ing great losses to the agricul- 

 turist. The loss from potato- 

 blight in New York state 

 alone often amounts in wet 

 seasons to over $10,000,000. 

 Warm weather is generally 

 favorable to fungus growth, 

 but there are some forms, 

 hke the potato-blight fungus, 

 which flourish only during 

 relatively cool periods. This 

 parasite occurs only in tem- 

 perate regions, being un- 

 known in the hot low lands 

 of tropical and subtropical 

 regions. The peach leaf-curl 

 fungus is apparently favored 

 as much by the low tempera- 

 ture as by the rains of a wet 

 spring. Other forms seem to 

 thrive best in dry climates, 

 as for example the powdery 

 mildew of grapes. 



While many fungi are de- 

 structive agents of the crops 

 of the agriculturist, causing him heavy losses, most 

 fungi are active co-laborers with him, bringing about, 

 as has been seen, the disintegration of compost, on 

 which the farmer depends so largely for increased crop- 

 production. Other fungi, like the yeasts and certain 

 molds, are necessary agents in the arts and manufac- 

 tures, as for example, the use of yeast in bread-, beer- 

 and wine-production, molds in cheese-ripening, and 

 so on. The value of these fungi lies chiefly in their 

 ability to produce fermentations of various sorts or to 

 give flavors to the products. Many fungi are edible, 

 as for example the large fruit bodies of mushrooms, 

 puffballs and truffles. While their value as food is 

 perhaps often overestimated, they are valuable and 

 form no unimportant part of the food of many 

 people, especially in Europe. They are to be regarded 

 chiefly as delicacies. The truffles and the cultivated 

 mushroom, Agaricus campestris, are perhaps the 

 best known. A deUcacy known to relatively few is 

 the large smut boils occurring on Zizania latifolia. 

 Some fungi are poisonous, as for example the deadly 

 Amanita, the fly-agaric among mushrooms, and the 

 ergot, a fungous parasite of rye and other grasses. 

 Fortunately the number of poisonous species is rela- 

 tively small. H. H. Whetzel. 



FUNGICIDES : Diseases and Insects. 



1611. Colonies of a fungus 

 on a plum leaf. The dead 

 tissue sometimes falls out, 

 leaving a shot-hole effect. 



