408 



THE CHANGING GENERATIONS 



of one of the oldest known vascular plants, of Devonian age, and many 

 sorts have been described from the stem tissues or leaves of Carboniferous 

 and later plants. The fungi are apparently an artificial assemblage in that 

 they are not closely related but seem to have arisen at different times 

 from different algal ancestors by loss of chlorophyll and assumption of 

 saprophytic or parasitic existence. 



Fig. 26.8. Photomicrograph of the fungus Penieillium, showing filamentous hyphae and 

 spores. (Courtesy General Biological Supply House, Inc.) 



ANCIENT LAND PLANTS 



To live upon land successfully a plant must possess certain things 

 that are lacking in the thallophytes. It must have a protective cuticle 

 to reduce loss of water by evaporation, and some means of absorbing water 

 from the soil. If it is to attain any size, a third thing is necessary — a 

 vascular system for carrying water from the buried to the exposed parts. 

 At some time during the early Paleozoic one or more groups of plants 

 made the transition from sea to land, but there are no fossils to show just 

 how it was accomplished. The green algae are thought to have been the 

 ancestors of land plants, because of similarities in cell structure and 

 the absence in land plants of pigments other than chlorophyll, such as 

 occur in the other groups of algae. Some of the multicellular green algae 

 became adapted to life in fresh water, and in consequence became sub- 

 ject to seasonal fluctuations of water level which at times left them 



