PEOTOCOCCOIDE^}. 47 



swarm-cells (zoospores, gametes, and spermatozoids) are con- 

 structed symetrically, and have true protoplasmic cilia, these 

 generally being attached to the front end of the swarm-cells. 

 Most of these Algae live in water (fresh or salt); some are found 

 upon damp soil, stones, or tree- stems, and some live enclosed in 

 other plants. 



The Class is divided into three families : 



1. PROTOCOCCOIDE^ : Volvocaceae, Tetrasporacese, Chloro- 

 sphaeracese, Pleurococcaceae, Protococcaceae, Hydrodictyaceae. 



2. CONFERVOIDE.ZE : Ulvaceae, Ulothricaceae, Chaetophoraceae, 

 Mycoideaceae, Cylindrocapsaceae, GEdogoniaceae, Coleochsetacese,. 

 Cladophoraceae, Gomontiaceae, Sphaeropleaceae. 



3. SIPHONED : Botrydiaceae, Bryopsidaceaa, Derbesiaceae, Yau- 

 cheriaceae, Phyllosiphonaceae, Caulerpaceae, Codiaceae, Valoniaceae,. 

 Dasycladaceae. 



Family 1. Protococcoidese. 



The AlgaB which belong to this group are nni- or multi-cellular 

 with the cells more or less firmly connected, sometimes in a. 

 definite, sometimes in an indefinite form (Fig. 47). Colonies are 

 formed either by division or by small unicellular individuals be- 

 coming united in a definite manner ; the colonies formed in this 

 latter way are termed Ccvnobia. Apical cells and branching are 

 absent. Multiplication by division ; asexual reproduction by zoo- 

 spores, rarely by akinetes. Sexual reproduction may be wanting, 

 or it takes place by isogamous, rarely by oogamous fertilisation. 



Some are attached by means of a stalk to other objects (Chara- 

 cium, Fig. 49), others occur as " Endophytes " in the tissues of 

 certain Mosses or Phanerogams, e.g. Chlorochytrium lemnce, in Lemna 

 trisulca ; Endosphcera., in the leaves of Potamogeton, Mentha aquatica, 

 and Peplis portula ; Phyllobium, in the leaves of Lysimachia num- 

 mularia, Ajuga, Chlora, and species of Grasses ; Scotinosphcera in 

 the leaves of Hypnum and Lemna trisulca ; the majority, however, 

 live free in water and in damp places. Many species which were 

 formerly considered to belong to this family have been proved to 

 be higher Algae in stages of development. 



Order 1. Volvocaceae. The individuals in this order are either 

 uni- or multi-cellular, and during the essential part of their life 

 are free-swimming organisms. They are generally encased in a 



mucilaginous envelope, through which 2-6 cilia project from every 

 \v. u E 



