92] 



The Classification of Lower Organisms 



are flat dichotomously branching thalli. In family Sargassea [Sargasseae] Kiitzing 

 there is a differentiation of holdfasts, stalks, blades, and floats. Growth is by division 

 of a single apical cell in each branch or member. There are the usual two tissues, a 

 superficial photosynthetic tissue of small cells and an inner tissue of larger cells which 

 pull apart to produce a spongy or fibrous mass. 



The gametangia are borne, mixed with sterile hairs, in pits called conceptacles. 

 These are clustered, in the Fucea near the tips of branches which have ceased to 

 grow (these tips are swollen, and are called receptacles), in the Sargassea on special 

 branches. Rarely, oogonia and antheridia occur in the same conceptacles; not infre- 

 quently, they occur in different conceptacles on the same individuals; commonly, they 

 occur on different individuals. Male and female conceptacles may be distinguished 

 by color, the male being orange-yellow, the female of the same dark color as the thalli. 



Male conceptacles are full of branching hairs bearing minute antheridia. In each 

 antheridium, the original single nucleus undergoes six successive simultaneous divi- 

 sions, producing sixty-four nuclei. These become the nuclei of sperms. Female con- 

 ceptacles contain fewer, larger, oogonia, in which the nuclei divide three times, pro- 



FiG. 17. — Microscopic reproductive structures of Laminaria yezoensis after Kanda 

 ( 1938) : a, male haploid individual releasing sperms; b, sperm; C, zoospore; d, female 

 haploid individual of three cells; e, female individual with an egg extnided from the 

 oogonium and attached in the mouth f, female individual with two young diploid 

 individuals attached at the mouths of oogonia. All x 1,000. 



