. Principles of modern biology. Biology. CHLAMYDOMONAS DESMIDS Fig. 31-2. Some green algae (Chlo- rophyta). Note the varied form, which may be unicellular, colonial, or multicellular. Also notice the nuclei and chloroplasts in the cells. Most green algae reproduce both sexually and asexually. ULOTHRIX (chlorophyll a and b, carotene, and xantho- phyll) are similar in the green algae and higher plants; and true starch is usually the intracellular storage product. The evolutionary status of the Chloro- phyta is still quite primitive, however. Only a few of the species can be regarded as multi- ce
. Principles of modern biology. Biology. CHLAMYDOMONAS DESMIDS Fig. 31-2. Some green algae (Chlo- rophyta). Note the varied form, which may be unicellular, colonial, or multicellular. Also notice the nuclei and chloroplasts in the cells. Most green algae reproduce both sexually and asexually. ULOTHRIX (chlorophyll a and b, carotene, and xantho- phyll) are similar in the green algae and higher plants; and true starch is usually the intracellular storage product. The evolutionary status of the Chloro- phyta is still quite primitive, however. Only a few of the species can be regarded as multi- cellular organisms. That is to say, most of the species are either unicellular or merely colonial. And even the multicellular forms display a very limited differentiation of spe- cialized cells and virtually no differentiation of tissues. In the sea lettuce (Fig. 31-2), for example, each large leaflike lobe of the thal- lus, which resembles a piece of crinkled, green waxed paper, consists of only two layers of cells, all more or less alike; and the hold- fast (and stalk) consists mainly of elongate colorless cells arranged in the form of twisted strands. And finally, a relationship between. LOBE OF THALLUS HOLDFAST the unicellular and the colonial species is clearly revealed by a study of the life cycle in forms such as Ulothrix. Most of the time this plant takes the form of a nonmotile filamentous colony. But at the time of re- production, when the zoospores are produced, it reverts to a unicellular motile status, pend- ing the formation of a new colony (Fig. 31-2). The Chrysophytes (Golden-brown Algae). The most important and widely known members of this group are the diatoms (Fig. 31-3). Most of the species are unicellular and nonflagellated, although a few do have fla- gella, and a few are colonial. Most of the species reproduce both sexually and asexu- ally; and generally the sexual reproduction is isogamous. Diatoms display several unique features. The cell wall is glassy a
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