54 MAN ON THE LANDSCAPE 



Green algae contain chlorophyll, and are useful as fish food, as 

 human food in their large forms, as laboratory culture media (agar), 

 and as household cleaners (diatom fossils). Certain fungi attach 

 themselves to algae and the combinations are found on trees, rocks 

 and raw soils as grayish-green lichens. These lichens are important 

 agents in breaking down rocks into soil by penetration of the rock 

 surfaces and by the acids they produce which dissolve alkaline rocks 

 or alkaline cement in others. 



Thallophytes reproduce by the primitive means of spores, tough 

 coated cells which may float in water or on the wind until, perhaps, 

 suitable conditions of food, moisture and temperature are found. 

 Food preservation and disease prevention are practical measures to 

 deal with some of them. On the other hand, to be productive of 

 aquatic life, a pond, lake, or stream must have them, and their 

 number depends in part on the mineral supply or fertility of the 

 water, which in turn depends on the quality, range, and availabilty 

 of minerals in the soil of the drainage area. 



Bryophytes. The moss plants and liverworts have a somewhat 

 obscure economic importance. They do play a part in developing the 

 environment for higher plants and for animals. They assist in soil 

 formation, and the sphagnum mosses form deposits of peat in old 

 lakes. These tufted, low growing plants are soft bodied, have a primi- 

 tive sort of leafy branches, but no true roots. They grow best in 

 damp places, some in water, but others can withstand drying. Re- 

 production is by spores (which assures wide distribution) and by 

 vegetative propagation (which means they grow and grow, mostly 

 sideways, as far as suitable habitat extends). 



Insignificant as we may consider these plants, they have rela- 

 tionships with other plants and with animals which elude the casual 

 eye. They are a step in the evolutionary development of the land- 

 scape to a point where it is valuable to man. 



Pteridophytes. Ferns and fern-like plants, such as club mosses 

 and horsetails, are similar to those of the carboniferous age when coal 

 measures were laid down. The cold and dryness of Permian glaciation 

 some 240,000,000 years ago wiped out most of them. These plants were 

 more highly organized than the thallus and moss plants. They ha<3 

 stems, leaves, roots and a vascular system enabling the circulation of 

 nutrients and water. They were well adapted to warm humid swamps 

 and grew to tremendous size; but, they were vulnerable to extreme 

 cold through unprotected leaf tips (where growth takes place) and 

 exposed reproductive organs. However, through mutations, some 

 have been able to survive in cold and dry regions. The ferns are 

 the most highly developed of the non-seed-bearing plants, and evi- 

 dence exists that some of the advanced tree ferns did produce seed. 

 All of the tree ferns associated with coal formation are extinct, al- 

 though there are a few modern tropical ferns which are of tree size. 



Here again, the importance of ferns living today lies not in direct 

 economic value but the part they play in vegetating the earth where 



