112 Plant Biology 



unicellular, some consist of long filaments composed of a linear series 

 of cells, and others consist of sheetlike masses of cells. Some of the 

 higher forms are even multicellular. In general, they do not possess 

 rigid tissues by means of which they can grow upward to any great extent. 

 Thallophytes do not possess true vascular (conducting) tissues (phloem 

 and xylem) which are present in higher plants. Spores are produced in 

 sporangia (spor -an' ji a) (Gr. sporos, spore; angios, vessel) which are 

 usually unicellular structures. When sex cells (gametes) are formed, they 

 are produced in gametangia (gam e -tan' ji a) (Gr. gametes, gametes or 

 sex cells; angios, vessel) which are usually unicellular structures. When 

 the tgg is fertilized to form a zygote, the latter does not produce a multi- 

 cellular embryo while still in the female sex structure. Many species of 

 thallophytes are of great economic importance, both detrimentally and 

 beneficially. Thallophytes include the algae (al'ge) (L. alga, seaweed) 

 and the jungi (fun'ji) (L. fungus, fungus, or mushroom). The algae 

 contain chlorophyll which, in the presence of energy-supplying light, is 

 able to combine carbon dioxide and water to produce carbohydrates 

 through the process of photosynthesis (fo to -sin' the sis) (Gr. phos, light; 

 synthesis, put together). The fungi lack chlorophyll and are unable to 

 manufacture their foods; they must depend upon outside sources for 

 their nourishment. The fungi will be considered later in this chapter and 

 in greater detail in a later chapter. 



As will be noted in the classification of plants, the first five phyla of 

 the subkingdom Thallophyta constitute the so-called "algae," while the 

 next three phyla constitute the so-called "fungi." Certain species of algae 

 will be considered more in detail in the next chapter. 



General Characteristics of Algae 



The term algae is applied to that group of thallophytes which possesses 

 chlorophyll by means of which photosynthesis may take place (Figs. 29 to 

 33). The algae vary greatly among themselves, and many of them even 

 resemble certain fungi in some respects. There are several characteristics 

 which are common to both algae and fungi, except that the former possess 

 chlorophyll while the latter do not. Algae are common in fresh water 

 (aquatic) and in salt water of oceans (marine). They may be free 

 living in fresh or salt water, where, together with the animals, they make 

 up the so-called plankton (plangk' ton) (Gr. plangktos, wandering). 

 Others may live on the bottom, where, together with the animals, they 

 constitute the so-called benthon (ben' thon) (Gr. benthos, depths of the 

 sea) . Certain species may grow in moist soils, on moist trees and rocks, 



