66 FIRST GROUP.— THALLOPHYTES. 



taceae, in which the process of sexual reproduction is equally unknown, we may 

 divide the Phaeophyceae into two groups ^ ; — 



1. Phaeosporeae or Phaeozoosporeae. 



2. Fueaceae. 



1. PHAEOSPOREAE. 



The Phaeosporeae "^ or Phaeozoosporeae are characterised by the circumstance 

 that the propagative cells, whether sexual or asexual, are always swarm-spores 

 of similar form and size. These are produced in sporangia of two kinds, the 

 plurilocular and unilocular. The former are divided by cell-walls into a large 

 number of small cells, each of which produces one swarm-spore ; in the latter the 

 protoplasm forms no cell-walls, but simply divides into a number of parts which 

 escape as zoospores. The two kinds of sporangia differ usually in form ; the uni- 

 locular are roundish or ovoid and usually dark-coloured bodies, while the plurilocular 

 are more elongate-cylindrical. In some species it has been ascertained that the swarm- 

 spores produced in plurilocular sporangia are sexually different and conjugate with 

 each other {Eciocarpus pusillus, E. siliculosus, Giraudia sphacelarioides, Scytosiphoii). 

 On the other hand this has never been proved of the swarm-spores produced from 

 unilocular sporangia, and these are most probably therefore asexual propagative cells. 

 There are moreover Phaeosporeae, in which only one kind of sporangium is known ; 

 thus Laminaria has only the unilocular kind, Scytosiphon and Phyleitis only the 

 plurilocular. 



The course of development in the Phaeosporeae may be depicted in some of the 

 better-known forms. 



a. The Ectocarpeae (including the Mesogloeaceae and Desmarestieae) have in their 

 simplest representatives, such as the genus Ectocarpits itself, a much-branched thallus 

 consisting of single cell-rows, and with the growing-point not at the apex of the fila- 

 ments but intercalary^ ; there is a row of cells beyond the growing-point, and these 

 cells, in proportion as they become further removed from the growing-point, lose their 

 protoplasmic contents and die off. The lateral branches on the main axis arise 

 acropetally on the part of the filament behind the growing-point, that is, their succession 

 is towards it* ; but if the growing-point, as often happens in lateral branches, is quite 

 basal, the lateral branches of successively higher orders arise in basipetal succession ; 

 in other words, their arrangement, with the exception of any that are adventitious, is 

 always towards the growing-point. This intercalary mode of growth obtains also in many 

 other Phaeosporeae, very plainly in Giraudia sphacelarioides, which may be regarded as 

 a more highly differentiated Ectocarpus. In this species young lateral axes are simple 

 cell-filaments, but eventually the cells at the upper end of the filament pass into the 

 permanent state, and divide now only by longitudinal walls, so that a tissue is produced. 



' [See also Rostafinski in Akad. d. Wiss. Krakau, i88i.] 



^ Thuret, Recherches sur les zoospores des Algues et las antheridies des Cryptogames (Ann. d. 

 sc. nat. Bot. iii. ser. T. XIV et T. XVI). — Derbes et Solier, Mem. sur quelques points de la physiol. 

 des Algues (Suppl. aux comptes rendus des seances de I'acad. d. sc. T. I\ — Goebel, Zur Kenntniss 

 einiger Meeresalgen (Bot. Zeit. 1878). — Berthold, Die geschlechtl. Fortpflanz. der eigentlichen 

 Phaeospor. (Mitth. aus der Zool. Stat, zu Neapel, Bd. II. 1881). 



^ Janczewski, Sur raccroissement du thalle des Pheosporees (Mem. de la soc. nat. de Cher- 

 bourg, t. XX). 



* Goebel, Ueber d. \'erzvveigung dorsiventraler Sprosse (Arb. d. bot. Inst, in Wiirzburg, Kd. II. 

 p. 390:. 



