30 INTRODUCTORY. PLANTS AND ANIMALS 



instance, are not green in colour, because the colour 

 of the chlorophyll is modified by the presence of other 

 pigments. They include the seaweeds, many of which 

 are large plants, with a considerable degree of internal 

 organisation, and the algae that live in freshwater, 

 most of which are pure green in colour, and consist of 

 simple filaments or single microscopic cells (see below). 



(5) The FUNGI, plants of about the same grade of 

 organisation as the algae, and, like them, comprising 

 a great range of size and complexity of organisation, 

 from the bulky mushrooms and toadstools to simple 

 moulds and mildews and minute microscopic forms. 

 They are distinguished by not possessing chlorophyll, 

 and they depend on organic food. 



(6) The LICHENS, peculiar compound plants, each 

 consisting of an alga and a fungus associated together 

 in one plant body, or thallus, which resembles in a 

 general way the liverwort thallus referred to above, 

 though it often branches in a complicated way. The 

 thallus of lichens is variously coloured : sometimes 

 the green colour of the included alga can be seen through 

 the fungal investment. Lichens are especially found 

 on rocks, the trunks of trees, or the bare soil. 



Many of the algae and fungi are microscopic, and some 

 of them are very minute indeed. Among these micro- 

 scopic forms, which live in water or some other liquid, 

 we come to the groups of organisms referred to on 

 pp. 23-4, which are on the borderline between plants 

 and animals, and are sometimes classed together as 



(7) The PROTISTA. Among these are the BACTERIA, 

 the smallest of all visible organisms, which are on the 

 whole plants, but many have the animal character of 

 locomotion. They are of enormous importance to 

 mankind, as we shall see in a later chapter. The 



