286 



STKTJCTURE AND LIFE HISTORIES 



species possess different colors, but they never possess 

 chlorophyll. 



275. Reproduction. — At a certain stage of development, 

 the Plasmodium will begin to form tiny upright stalks, 

 at the top of which will develop a spore-case, containing 

 spores and capillitium (Fig. 209) . The capillitium consists 

 of hygroscopic threads which aid in the dissemination of 

 the spores. When the spores are ripe they are scattered 



Fig. 210. — Kohlrabi, showing club-root, caused by a myxomycete, 

 Plasmodiophora brassies. (Cf. Fig. 2.) 



by the wind, and each, on germination, produces a swarm- 

 spore. A new Plasmodium results from the fusion of these 

 swarm-spores. 



276. Economic Importance. — The Myxomycetes have 

 very little economic importance, but the disease of cab- 

 bages, kohlrabi, and turnips, known as club-root, is caused 

 by a slime -mold growing on the roots (Fig. 210). 



277. Bacteria. — The bacteria are among the very 



