THALLOPHYTA: ALGAE 87 



cells, a feature of all the red algae, are called spermatia. The female sex 

 organs, or carpogonia, also arise from ordinary vegetative cells hut without 

 undergoing division, the protoplast functioning directly as an egg (Fig. 

 730. 



A spermatium, carried by water currents to the carpogonium, enters 

 and fuses with the egg. The zygote divides at once to form a group of 

 spores, usually 8 or 16, that are freed by the breaking down of the surround- 

 ing cell walls (Fig. 7SC-E). These naked cells are carpospores and, like 

 the gametes, are nonciliated. The freed carpospores exhibit an amoeboid 

 movement (Fig. 73F). After coming to rest, each carpospore forms a cell 

 wall and develops into a new thallus. The reduction of chromosomes 

 occurs when the zygote germinates, and so the vegetative plant is haploid. 



As compared with the higher orders of Rhodophyceae, the Bangiales 

 have a simple type of nucleus and cells without evident protoplasmic 

 continuity. They display intercalary rather than apical growth. The 

 carpogonium either lacks a trichogyne or has a very short one. The 

 zygote is transformed directly into carpospores. An alternation of 

 generations is not present. 



Porphyridium is a unicellular alga whose relationships are uncertain. 

 It forms a reddish gelatinous layer on damp soil and moist walls. It was 

 formerly placed in the Cyanophyceae but, because it has a true nucleus 

 and a distinct plastid, is now included in the Rhodophj^ceae. The cells 

 are spherical and surrounded by a mucilaginous matrix. Fission is the 

 only know^n method of reproduction. 



Nemalion. Although showing a considerable advance over Porphyra, 

 this form is much simpler than members of the higher orders. Nemalion 

 is wddely distributed, growing on rocks between the high- and low-tide 

 lines. The thallus, up to 60 cm. in length, consists of a slimy mass of 

 branching filaments that are interwoven to form a worm-like cylinder. 

 This is composed of a central core of slender colorless filaments from 

 which tufts of larger chlorophyllose filaments radiate outward. The 

 cells of the latter have a small nucleus and a large plastid with a con- 

 spicuous pyrenoid. As in all the algae except the Bangiales, growth is 

 apical. Furthermore, the vegetative protoplasts are connected by a 

 conspicuous strand of cytoplasm that passes through a pore in the cell 

 wall. 



Nemalion is monoecious, the sex organs occurring at the ends of short 

 branches. The antheridium consists of a single small cell that is budded 

 off laterally from an antheridial branch (Fig. 74A). Its protoplast, the 

 spermatium, is discharged into the water. The female organ, called a 

 procarp, consists of two parts, the carpogonium and the trichogyne (Fig. 

 745). The protoplast of the carpogonium functions as an egg. The 

 trichogyne is a long thread-Uke cell at the upper end of the carpogonium. 



