THE RED ALGtE 487 



made up of cells still capable of division is termed a mei-istem,' 

 or is described as meristematic, while a fully differentiated 

 tissue is distinguished as -permcment. 



Laminaria reproduces only by swarm-spores which are formed in 

 sac-like sporangia projecting from the surface of the pseudo-leaf. 

 They are crowded closely, together with a number of curiously 

 shaped protective cells called paraphyses.^- The swarm-spores have 

 a red eye-spot and two flagella which arc attached at the side. 

 There are no gametes. 



A somewhat higher development both of the vegetative and re- 

 productive systems is found in the genus Fucus (Figs. 318, 319) 

 which includes the common " bladder- wracks " of the sea-shore, 

 so called because of the bladder-Uke floats (l) developed in the 

 thallus. The meristematic tissue is at the tip of the thallus-lobcs. 

 A disk-like pseudo-root attaches the thallus to rocks which lie mostly 

 between tides. The pseudo-shoot has forking midribs with flat 

 expansions on either side in which the inflated bladders often appear. 

 There is a rind and an inner, somewhat pith-like tissue much as in 

 Laminaria. The tips of certain branches become swollen (.s. Fig. 318) 

 and produce a number of small cavities (conceptacles) each opening 

 ))y a pore at the surface and lined with numerous paraphyses among 

 which appear either male or female gametangia (Fig. 319, a). Within 

 a female gametangium (6, c) eight large, spherical, non-fiagellate 

 gametes arise and are pressed out into the surrounding water by swell- 

 ing of the paraphyses. The male gametangia, (d) expelled at the same 

 time emit numerous flagellate gametes {§) which resemble somewhat 

 the swarm-spores of fjaminaria. They are attracted in large num- 

 bers to a female gamete, and, attaching themselves to its surface, 

 often cause the sphere to revolve by the energetic movement of their 

 flagella (e). Dircctlj^ after fertilization the oospore comes to rest and 

 germinates (/), attaching itself to some rock by projections which 

 form the beginnings of a pseudo-root, while the main part above 

 becomes a meristem for the shoot. No swarm-spores are produced 

 and there is no alternation of generations. 



176. The red algae (Class Rhodophyceas) , the largest 

 and one of the most highly developed groups of seaweeds, 

 are characterized by the presence of a red pigment called 

 phycoerythrin,^ which very generally masks the chlorophyll 

 completely. The carrageen already studied (page 112) belongs 

 to this class. 



1 ^ler'is-tcm < Gr. merislos, divisible. 



^ Pa-raph'y-ses < Gr. para, besides; plu/^is, growth. 



^ Phy"co-er'y-thrin < Gr. crythros, red. 



