■fPi^OPHYOlAE. , 191 



D. PHAEOPHYCEAE (bbown algae), 



. Olive- brown algae, thallus often leathery in texture, composed 

 of cell-filaments or parenchymatous tissue, in some cases exhibit- 

 ing a considerable degree of internal dijfferentiation. The 

 sexual reproductive organs may be either in the form of passive 

 egg-cells and motile antherozoids or of motile cells showing no 

 external sexual difference. 



With one or two exceptions all the genera are marine. 

 They have a wide distribution at the present day, and are 

 especially characteristic of far northern and extreme southern 

 latitudes. The gigantic forms Lessonia, Macrocystis and others 

 already alluded to, belong to this group ; also the genus 8ar- 

 gassum, of which the numberless floating plants constitute the 

 characteristic vegetation of the Sargasso Sea. 



* Palaeobotanical literature is full of descriptions of supposed 

 fossil representatives of the brown algae, but only a few of the 

 recorded species possess more than a very doubtful value ; most 

 of them are worthless as trustworthy botanical records. Many 

 of the numerous impressions referred to as species of Fucoides^ 

 and other genera present a superficial resemblance to the thallus 

 of the common Bladder-wrack and other brown seaweeds. 

 Such similarity of form, however, in the case of flat and 

 branched algal-like fossils is of no scientific value. In many 

 instances the impressions are probably those of an alga, but 

 they are of no botanical interest. The flat and forked type of 

 thallus of Fucus, Ghondrus crispus (L.) and other members of 

 the Phaeophyceae is met with also among the red and green 

 algae, to say nothing of its occurrence in the group of thalloid 

 Liverworts, or of the almost identical form of various members 

 of the animal kingdom. The variety of form of the thallus in 

 one species is well illustrated by the common Ghondrus crispus 

 (L.). This alga was described by Turner' in his classic work on 

 the Fuci under the name of Fucus crispus as " a marine 

 Proteus." It affords an interesting example of the different 

 appearance presented by the same species under different con- 

 ditions, and at the same time it furnishes another proof of the 

 1 Turner (11) vol. ii. p. 51. 



