06 



PLANT MORPHOLOGY 



nuclei degenerate. Upon germination, the zygote sends out a simple 

 green filament and a colorless rhizoid. The adult shoot arises from this 

 filament as a lateral branch. 



Summary. The Charophyceae are an aberrant group, standing apart 

 from the other algae. They resemble the Chlorophyceae in containing 

 an excess of chlorophyll over the carotinoids and in storing starch as 

 reserve food. The vegetative body is distinctive, being an erect thallus 

 differentiated into nodes and internodes and with two kinds of branches 



A B 



Fig. 53. Chara. A, longitudinal section of a young oogonium, invested by a sterile jacket, 

 and a young antheridium, the latter consisting of a stalk cell, an outer layer of shield cells, 

 four middle cells (manubria), and four inner cells (primary capitula), X200; B, a shield 

 cell from a mature antheridium with manubrium projecting from it. At the tip of the 

 manubrium is a primary capitulum to which are attached smaller secondary capitula, each 

 bearing a pair of spermatogenous filaments. 



arising at the nodes. There is no reproduction by spores. The sex 

 organs are multicellular and complex, both being enclosed by a jacket of 

 sterile cells. In this respect the Charophyceae resemble the bryophytes, 

 although the development of the sex organs in the two groups is very 

 different. The sperms are also like those of bryophytes. 



9. PHAEOPHYCEAE 



The Phaeophyceae, or brown algae, are nearly all marine in distribu- 

 tion, occurring along most seacoasts but reaching their greatest display in 

 cool waters. They range in color from olive green to dark brown as a 

 result of the presence in their cells of chlorophyll and an excess of carotin 

 and a unique xanthophyll, fucoxanthin, which is brown. There are no 

 unicellular brown algae. Their multicellular bodies may be filamentous, 

 plate-like, or may reach massive proportions and be highly differentiated 

 in form. They are always attached. The Phaeophyceae are a special- 

 ized group, probably derived independently from flagellate ancestors and 

 apparently not related to any of the higher plants. There is no satis- 



