30 REPRODUCTION 



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. 



5. 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 pufT-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 



