FUCUS. 49 



each of which may develop into a branch of the 

 thallus similar to the original : thus the branching is 

 a dichotomy. 



C. On comparison of a number of branches it may be 

 seen that the development of the two branches of a 

 dichotomy is not equal, one being usually stronger than 

 the other : this leads to a sympodial development of 

 the dichotomous branch-system. 



D. Observe the less regular outline of the ends of 

 those branches which bear conceptacles, the latter 

 being seen in large numbers on those branches : note 

 with a lens the round orifice or ostiole in the centre of 

 each conceptacle. When mature, two kinds of con- 

 ceptacle may be recognised in this species ; they are 

 borne on different plants : and this species may accord- 

 ingly be recognised as dioecious. 



a. Conceptacles the contents of which are of a dark 

 olive-green : these contain the oogonia, and are the 

 female conceptacles. 



~b. Others with yellow or orange contents : these are 

 the male conceptacles, and contain the antheridia. 



Of other common species of Fucus, it is to be noted that in 

 F. vesiculosus there are numerous air-bladders in the tissue of 

 the thallus, that the conceptacle-bearing branches are swollen, 

 and that the distribution of the sexual organs is as in F. serratus, 

 the plant being dioecious : in F. platycarpus, on the other hand, 

 male and female organs are found on the same plant and in the 

 same conceptacle, while the fertile branches are, as in 

 F. vesiculosus, considerably swollen. 



E. If those flattened parts of the thallus be examined 

 which do not bear sexual conceptacles, there will be 

 found, scattered here and there, organs of somewhat 



E 



