Minnesota Plant Diseases. 



105 



the water, drive the spore forward with a combination of a hop- 

 ping, whirHng and swimming motion. These spores, when 

 they come to rest, draw in their whips and immediately grow 

 out into the mature plant. The function of the resting spores, 

 whether a breed-spore or not, is to tide the plant over unfavora- 

 ble seasons. When breeding occurs, the two breeding organs are 

 exactly alike and indistinguishable, as is the case in some pond 



scum algae. These lowly fungi are 

 found in a great variety of habitats. 

 Most of them are parasitic, though 

 some are saprophytes. They are 

 found on algae as well as on lowly 

 water animals or on the eggs of the 

 latter. Some are found on fungi, par- 

 ticularly on water and fish molds, 

 while a large number inhabit the 

 leaves and stems of the flowering 

 plants. In their parasitic habitat they 

 often arouse the host to extraordi- 

 nary growth and swellings or galls are 

 thus produced. Hence they are some- 

 times known as gall fungi. Galls of 

 this nature are produced on the leaves 

 of dandelion, anemone and on garden 

 plants such as cabbage. Few, how- 

 ever, produce diseases of very great 

 importance. In that they damage 

 algae and water animals in the waters of fish hatcheries they 

 injure or diminish the food supply of the young fish. One spe- 

 cies attacks and gains entrance to pollen grains of the pine 

 when the latter lie on the surface of water or are submerged in 

 ponds, and lives inside of the spore until it forms its swimming 

 spores when the latter are thrown out into the water. Some 

 have even learned to penetrate and to live in the pill-box algae, 

 which are provided with walls of silica. (Figs. 41, 211.) 



Water molds and fish molds(S aprolegniinecF in part). These 

 fungi are more highly organized than the group of fungi just 

 discussed. In the first place they all possess a branched and 

 well developed system of thread mycelium. They are, how- 



FlG. 41. — A lowly algal fungus. 

 Above, the resting condition 

 of a single-celled fungus in 

 the tissues of the host plant. 

 Below, young fungus plants 

 are seen in the cells of the 

 host. Highly magnified. 



After Schroeter. 



