198 PRACTICAL LESSONS IN SCIENCE. 



reproductive apparatus, has the sanction of the latest and best 

 authorities. 



These plants show no indication of true roots, stems or leaves. 

 They are made up mainly of parenchyma cells showing no 

 wood cells, tubes or other characteristics of stems. Yet while 

 they are low in form and structure, and are of comparatively 

 small economic value, they are numerous, far exceeding the num- 

 ber of the higher plants. We cannot learn many things about 

 them by examination with the naked eye; but what we can learn 

 is of great interest, leading us into comparatively untrodden 

 fields of nature. 



Among these cellular plants the nutritive processes go on in 

 all parts of the organism, there being little or no division of 

 labor, each cell acting a.s an individual. In the study of these 

 plants we have found three classes: the chlorophyll plants that 

 absorbed their nourishment, as carbon dioxide, water, etc., from 

 the mineral kingdom these in the sunlight were changed into 

 such compounds as the plant could build into tissue; others, 

 called parasites, absorbed compounds already prepared for use 

 from the juices of chlorophyll plants, and from them built up 

 their tissues; others called saprophytes absorbed compounds 

 from decaying vegetable substances, from which their tissues 

 could be nourished. 



The members of this group of plants affect man in various 

 ways; directly, in causing such diseases as intermittent, typhoid, 

 yellow, scarlet and typhus fevers, cholera, smallpox, croup, con- 

 sumption, erysipelas, and many other diseases; and indirectly, 

 in causing diseases of domestic animals, as splenic fever, fowl 

 cholera, swine fever, rabies, glanders and others. And they are 

 the cause of the various kinds of fermentation, some of which 

 are valuable and some harmful. Some fungi are valuable for 

 food, but many of them are injurious. They cause skin diseases, 

 as ringworm. They infest almost every useful plant, lessening 

 the quantity of the food product, injuring its quality, as in the 

 case of the rust of wheat, the potato fungus and those which 

 infest the grape. 



