STUDIES OF SPORE-PLANTS 255 



(called zygospore, or gametospore), which like the fertilized 

 egg-cells of mosses, ferns, seed-plants, and animals, is com- 

 posed of protoplasm from two sources. In short, this 

 zygospore is a simple kind of fertilized egg-cell. It germi- 

 nates much like an ordinary mold spore, and forms hyphae 

 which develop aerial branches with ordinary spore-cases. 

 Apparently the reason for this process, known as conjugation 

 of molds, is the same as that for fertilization in other plants 

 and in animals; namely, that there is some physiological 

 advantage in new individual organisms beginning from a 

 mass of protoplasm which has two parents. The significance 

 of this is in part a problem of heredity, which will be pre- 

 sented in the last chapter. 



As a rule, molds grow best in a warm place, as can be 

 proved by leaving pieces of moist bread in two bottles, 

 one of which is placed near a stove or radiator, and one in 

 an ice-box. However, some molds will grow on foods kept 

 for some time in the ice-box, and one kind forms the slimy 

 material which grows in the drain-pipes of ice-boxes and 

 clogs them unless cleaned frequently by hot water and wash- 

 ing powder. 



245. Experiments with Molds. (D or L) Test-tubes by 5 

 inches are best for these -experiments, but bottles with mouth at 

 least \ inch in diameter will do. Cut some strips of bread i by 2 inches 

 in size, and place one in each of ten or more tubes, and add three or 

 four drops of boiled water to each tube. Now, plug the mouths of 

 the tubes with cotton-batting or absorbent cotton, making the plugs 

 by rolling the cotton into a cylinder about two inches long. Have 

 the plugs of a size which will fit rather loosely in the tubes, else 

 after steaming the cotton will swell and the plugs will be forced 

 out. Fold the projecting cotton over the edge of the tube, so as 

 to keep dust from falling on the edge. Experiments tried thousands 

 of times have shown that spores and microscopic organisms cannot 

 get through such plugs of dry cotton, and that the tubes are as 

 effectually closed as if the/ were hermetically sealed by melting the 

 glass. Also, the cotton has the advantage of allowing the entrance 

 of air, which is needed by molds that grow in the tube. 



