THE ALGAE 171 



species, though not in C. ruhriim, spines may also be developed at the nodes 

 in connection with the primary cortical cells. These spines consist of 

 tapering filaments of about four or five cells. Secondary spines may be 

 developed above and below the primary spines. These consist of only 

 about two cells, and project upwards and downwards at an angle with the 

 cortex. 



The organ of attachment in C. riibrum develops from the basal cell of the 

 germinating tetraspore or zygote respectively, which elongates and then 

 divides to form a number of rhizoids, each of which becomes multicellular, 

 and forms a flat plate of tissue by means of which the plant is firmly fixed 

 to the substratum of rock. Frequently a number of separate shoots arise 

 from a common basal attachment. 



Sexual Reproduction 



The sex organs are developed on different plants. The female sex organs 

 are developed terminally on short lateral branches. The groups of carpo- 

 spores are partly protected by a number of short branches which are formed 

 laterally and grow up to surround, at least partially, the carpospores. No 

 cystocarp envelope is formed. The antheridia are not produced on special 

 organs but are scattered in patches over the surface of the thallus. 



The Antheridium 



The antheridia arise by the division of cortical cells. In the younger 

 regions every cortical cell may function, but in the older parts of the thallus 

 antheridia formation is limited to the cortical cells of the nodes. Each 

 cortical cell divides first by the formation of periclinal w'alls and then by 

 anticlinal ones, thus cutting up the cell into four or five cells, each of which 

 functions as an antheridium mother cell. This cell next elongates and 

 forces its terminal part through the gelatinous covering, forming a pro- 

 tuberance which is gradually abstricted at its base. This is the antheridium 

 (Fig. 163). It is enclosed in a rather thick gelatinous wall which increases 

 greatly in thickness at the apex. The antheridium itself contains a single 

 nucleus enclosed in rather dense cytoplasm. A split occurs in the apex of 

 the antheridial wall and a single spermatium slips out. 



Meanwhile a projection of the antheridial mother cell grows out and 

 forms a second antheridium, and before the discharge of the second 

 spermatium a third projection may arise. This process appears capable of 

 successive repetitions, until after the production of about six spermatia the 

 mother cell becomes exhausted. 



The spermatium contains a single nucleus ; it is oval, and the blunt apex 

 is occupied by the nucleus while the rest is largely filled with vacuolate 

 cytoplasm. It is enclosed in a delicate wall. 



