they are attracted by the chemical changes in the water 

 due to the decaying flesh, and so very many of them do 

 not get away from this attractive spot. Thus a very 

 luxuriant growth occurs in a very brief time on the fish. 

 This fact produces the disease and death of many fish, 

 but it means that the, mold is being successful. 



3. The Effect of the Medium on the Method o£ Scattering. 

 Plants producing spores grow in air, in water, and in 

 solids, as soil, etc. In the last case, however, it usually 

 happens that the plant sends the spore-bearing branches 

 to the surface, so that the spores are set free either in 

 the air or in water. The problem of scattering the spores 

 must be solved differently in the air and in the water. 

 The water is more heavy and supports the spores better. 

 Furthermore, it keeps them moist, and spores prepared to 

 live in water need not have such thick walls. They may 

 indeed lead a very active life, swimming here and there 

 quite independently of the currents in the water. This is 

 true of many spores of algae and of a few furtfei. If they 

 are not motile and are lighter than water, they may float 

 at the surface and be carried long distances by the 

 currents. 



The spores of the majority, of the fungi, however, are 

 adapted to the air. They are set free as a dry powdery 

 mass. You doubtless have seen the dense powder arise 

 from a broken puff-ball. This is made up of the thousands 

 of spores which it forms. They have coats which prevent 

 too great loss of their moisture by evaporation, are not 

 actively alive while in the atmosphere, have no motion of 

 their own, and are a little heavier than air, so that in 

 still air they settle to the earth. When the air is in 

 motion, however, they are carried far and wide. They 

 may be dropped temporarily, but unless they fall in a 

 moist place suitable for their germination so that they 

 take hold on the solids, they are readily picked up again 

 and carried on. It is perfectly safe to say that spores 

 may be carried hundreds of miles in times of high winds. 



4. The Special Methods of Scattering Spores. The 

 following classification of the methods by which spores 

 are scattered will enable the student to see the variety. 

 Some of these methods are more effective than others, 

 but the sum of all is to make plants very widely 

 distributed. 



A. Spores carried by the air. 



1. Without any aid from the plant itself, such as 

 a projection of the spores into the air by some 

 explosive act. 



2. Spores driven to some distance from the parent 

 plant by the presence of some explosive change 

 in the plant itself. 



B. Spores carried by water. 



1. Spores are passively carried by currents of water. 



2. In addition to the water currents, some spores 

 have a power of motion of their own. 



C. Spores carried by various special moving objects. 



1. By adhering to seeds of plants that are carried 

 by wind, water, etc. 



2. Carried by insects, birds, and in less degree by 

 other animals. 



3. Carried by man in his commerce, agricultural 

 operations, and the other artificial transportation 

 of materials from one part of the country to 

 another. 



S. Air-Borne Spores. Spores to be best adapted to 

 being scattered in this way must be freed in a dry, 

 powdery form. They may be carried singly or in loose 

 masses. That they are so carried is readily shown by 

 exposing culture plates to the air, and later placing these 

 in conditions favorably for germination. This proves 

 that there are plenty of such spores being carried by the 



air. Often a number of species may be discovered on one 

 plate. Great numbers of spores are necessary to make 

 this an effective way to spread a species. The chances 

 are very much against the success of any particular spore. 

 They are produced in unthinkable numbers. Cobb 

 estimates that as many as 500,000,000 spores may be 

 produced from a single head of smutted oats. It is said 

 that the giant puff-ball produces as high as 7,000,000,000,000 

 spores. Of course nobody ever counted these. A certain 

 small mass is counted under a microscope and the whole 

 mass estimated from this. 



Many plants bearing spores have some elastic tissues 

 that cause an explosion when the spores are ripe. In this 

 way they puff the spores into the atmosphere. Here they 

 are much more sure to be picked up and carried away by 

 the wind, since most such plants grow within or upon 

 the surface of the earth or of other solids. 



6. Spores Scattered by Water. Reference has already 

 been made to the free-swimming spores of the water 

 molds and algae, and to the carrying of spores by running 

 water. Water is absolutely necessary for the first kind. 

 Some swimming spores are known to find their way from 

 plant to plant through the water in the soil itself, 

 especially soon after rain or heavy dew. This is true of 

 the fungus causing the "damping-off" of seedlings. Many 

 parasitic plants that attack seed plants exude their spores 

 in moist weather, and rains wash them down from the 

 leaves and bark. Thus they are carried to new parts of 

 the same plant, or to other plants, by first infecting the 

 soil about them. 



7. Spores Carried by Insects, Birds. Etc. A number of 

 fungi attack fruits, seeds, leaves, and other parts of plants. 

 Insects and birds may use these for foods. These animals 

 carry spores of these fungi from an infected to an 

 uninfected plant, very much as they carry pollen from 

 flower to flower. The spores adhere to the feet and to the 

 mouth parts particularly, and these are the parts most 

 likely to bring them in contact with fresh surfaces. 

 Furthermore, insects may feed directly on the fungi and 

 necessarily carry away spores and distribute them widely. 



8. Spores Disseminated by Man. Man, in his mastery 

 of the earth and in his exchange of its products, is sure 

 to distribute spores. Soil spores are carried far and wide 

 by plowing and harrowing, by tools and wheels of 

 vehicles, and by the transportation of soils and manures. 

 The shipment of infected nursery stock, seeds, and fruits 

 is responsible for the wide distribution of the spores of 

 many fungi that attack plants. Similarly, the shipping of 

 hay, grain, vegetables, and any of the raw food products 

 tends to spread any spores that are on these plants. 

 Certain kinds of fungi have thus followed man very 

 closely in his movements around the earth. 



CHAPTER SEVEN. 

 SOME SPECIAL KINDS OF MULTIPLICATION. 



1. General. There are some special methods whereby 

 organisms multiply themselves which are rather common 

 but do not exactly fall under any of the heads discussed 

 above. In some respects they may be thought of as 

 forms of budding, but they are not exactly so. They 

 occur in so many different plants and in so many different 

 ways that it seems desirable to describe them separately. 



