MetapJiyta F 11 ens. 8 5 



to he supposed that there is no chlorophyll present. Its 

 presence is masked by an admixture of a brown colouring- 

 matter. It performs the same function as the unmixed 

 chloropKyll of Spirogyra. The carbonic acid is, of course, 

 as in the case of Spirogyra, obtained from the water (in this 

 case salt-water), and the various physiological processes are 

 conducted as in that type. 



Reproductive organs. The reproductive apparatus of 

 Fucus is of a very complete and highly differentiated nature. 

 At the proper season, certain (usually many) of the branches 

 exhibit at their terminations swellings which are covered 

 over with minute mounds or pimples. These are fertile 

 branches, and the pimples represent the mouths of small 

 depressions or sacs ('conceptacles') sunk in the tissue of the 

 thallus. Each sac contains (in F. platycarpus] both male 

 and female cells. If a vertical section of a sac be examined 

 (fig. 24) it will be found to consist of a bounding wall of cells 

 not unlike, and continuous with, the cells forming the super- 

 ficial layer of the thallus, from which spring numerous hairs 

 of variable shape some long and branching, others thick, 

 short, and in some cases almost spherical. These are respec- 

 tively the spermaria, or sperm-producing organs, and the 

 ovaria, or ovum-producing organs. The cavity of the sac 

 is filled with sea-water, mingled with the mucus secreted 

 from the slimy tissue of the thallus. 



A more careful examination of the hairs in the sac dis- 

 covers that they spring from the lining-wall of the sac, and 

 that, since the sac itself is formed in all probability by an 

 indentation or imagination of the superficial cells, 1 the 

 reproductive hairs are really equivalent morphologically to 

 superficial or epidermal hairs. 



Taking the male elements first, we find that the sperms 

 (fig. 25) are minute unicellular bodies without any visible 



1 According to Bower, Q.J.M.S. 1876, the formation of the con- 

 ceptacle, at least in some forms, commences with the decay of a super- 

 ficial cell. 



