238 



PART III. THE CLASSIFICATION OF PLANTS. 



differentiated as reproductive organs (Volvox). Eudorina is dioecious, the cells 

 of the body of any one individual becoming either all oogonia or all antheridia ; 

 Volvox is sometimes monoecious, sometimes dioecious. The contents of the 

 oospore undergo repeated bipartition until the requisite number of cells to 

 form a new individual is attained. The vegetative development of new indi- 

 viduals from the body-cells of Eudorina, and from the special gonidial cells of 



Volvox, takes place in 

 precisely the same way 

 as the development from 

 the oospore. In Volvox, 

 the small individuals 

 formed vegetatively from 

 the gonidial cells are set 

 free into the cavity of 

 the parent, where they 

 remain until it dies, when 

 they are set free. The 

 spermatozoids of Volvox 

 and Eudorina are club- 

 shaped, yellow, with a 

 red eye-spot (see p. If 2), 

 and bear two cilia, either 

 at the pointed end (Eu- 

 dorina), or inserted la- 

 terally (Volvox). 



Series III. SIPHONOI- 

 DE^E. The forms in- 

 cluded in this series 

 may be arranged in the 

 three following orders : Siphonaceee, Cladophoraceae, Hydrodictyaceae. 



Order 1. Siphonaceae. The body is an unseptate coenocyte, septa being 

 only formed in connexion with the development of reproductive organs ; it is 

 usually attached, and presents a considerable variety of form ; it may be thalloid 

 and then be tubular and much branched (usually in Vaucheria, Fig. 169, 

 Phyllosiphon) ; or it may be differentiated into root and shoot, the shoot 

 assuming various forms, such as a rounded cushion (Codium liursa), or a 

 simple vesicle (Botrydium, Fig. 171); or the shoot maybe differentiated into 

 stem and leaf (Acetabularia, Fig. 170, Bryopsis, Caulerpa. Fig. 162); it has 

 sometimes continuous apical growth (e.g. Vaucheria) ; the wall is sometimes 

 impregnated with chalk (e.g. Halimeda, Acetabularia). 



Asexual reproduction is known to take place in only a few forms : it is 

 effected by zoogonidia in Botrydium, where they are uniciliate ; in Vaucheria, 

 where they are multiciliate (see Fig. 75) ; in Derbesia, with a group of cilia at 

 the anterior end ; in Halimeda, where they are biciliate ; in Phyllosiphon, which 

 is endophytic on Arisarum vulgare, it is effected by non-motile gonidia, as it is 

 sometimes also in Vaucheria. In Vaucheria the gonidia are formed singly in 

 simple gonidangia formed by septation of branches of the body ; in Botrydium 

 and Phyllosiphon they are formed in large numbers, in the former from the 



Fis. 168. Volvox Globator (after Cohn ; x about 100), 

 monoecious, with antheridia a, and oogonia 6. 



