262 



GENERAL MORPHOLOGY OF PLANTS 



the members of the class can usually be recognized by their reddish 

 or reddish purple color. The red algae are usually found in deeper 

 water than the brown or green algae, occupying the lower zone of 

 the alga-inhabited region below ebb tide, where the waters are 

 more dimly lighted. The red algae are more sensitive to bright 

 light than the brown and green and suffer discoloration in the 

 brighter light region. In the shade they grow nearer the surface. 

 Some species are bright red when growing in the shade, or dull 

 red when they grow in brighter light. 



400. Nemalion.- The plant body of nemalion is a slender, 

 cylindrical, branched shoot. The central strand is firm and 

 composed of delicate threads. It is covered by a cortex of loose 

 filaments which arise as lateral branches and extend outward. 



It represents the 

 simplest type of sex- 

 ual reproduction in 

 the red algae, though 

 there are filamentous 

 forms with a much 

 more simple struc- 

 ture of the thallus, 

 i.e., the plant body. 

 The sexual organs. 

 The male organs, or 

 sperm cases (anther- 

 idia), are small 

 rounded cells borne 

 in crowded clusters, on short branches, at the end of a 

 branch. Each sperm case contains one or two non-motile 

 sperms. The female organ. This is borne on a special branch 

 of four or five cells, called a procarp. The terminal cell is the 

 egg, but is called a carpogonium in the red algae, because it 

 gives rise to a fruit body, the cystocarp. It is extended into a 

 long slender process called the trichogyne, or egg hair. The 

 egg with its hair thus resembles very closely the egg case of Coleo- 

 chaete. Fertilization. In fertilization a sperm comes in contact 



Fig. 213. 



Batrachospermum ccerulescens. Natural size. It grows 

 during the summer season in slow running water. 



