66 FIRST GROUP. THALLOPHYTES. 



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

 divide the Phaeophyceae into two groups l ; 



1. Phaeosporeae or Phaeozoosporeae. 



2. Fucaceae. 



1. PHAEOSPOREAE. 



The Phaeosporeae 2 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 (Ectocarpus pusillus, E. siliculosus, Giraudia sphacelarioides, Scytosiphori). 

 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 gvcmsEctocarpus itself, amuch-branched thallus 

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

 ments but intercalary 3 ; 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. 



1 [See also Rostafinski in Akad. d. Wiss. Krakau, 1881.] 



3 Thuret, Recherches sur les zoospores des Algues et les 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 1'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). 



3 Janczewski, Sur 1'accroissement du thalle des Pheosporees (Mem. de la soc. nat. de Cher- 

 bourg, t. XX). 



4 Goebel, Ueber d. Verzweigung dorsiventraler Sprosse (Arb. d. bot. Inst. in Wiirzburg, Bd. II. 

 p. 390). 



