CONFERVOIDE.E ISOGAM.E 



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marked as in the unicellular Multinucleatae. The class includes one 

 large order, the ConfervacecB, and three smaller ones, the Ulotrichacece, 

 FithophoracecE, and Chroolepidece^ though the boundaries between them 

 are not in all cases well defined. In the Confer\-ace8e and Ulotrichaceae 

 the filament which springs from the germination either of a zoospore 

 or of a zygosperm resulting from the conjugation of zoogametes, attaches 

 itself to the substratum — a stone, another alga, or some other aquatic 

 plant — by a rhizoid, which may consist of a single cell, or may branch 

 into a number of cells. As in the higher algae, the rhizoid is not a 

 nutritive organ, but simply an organ of attachment. These algae may, 

 however, continue to grow and retain their vitality for a long period in 

 water without any attachment to the substratum. 



Order i. — Confervace.^ (?>/^/?^^/-^^ Ch.etophorace.^). 



The term Confervacese has been very 

 vaguely applied to a variety of green fresh- 

 water organisms, but is now limited to a 

 comparatively small number of genera of 

 fresh-water, and a few brackish and salt- 

 water algje, in which each individual 

 consists of a segmented branched or un- 

 branched filament of cylindrical or disc- 

 shaped cells, invested by a mucilaginous 

 sheath, and in which multiplication takes 

 place non-sexually by 7)iegazoospores^ or 

 sexually by the conjugation of smaller 

 zoogametes. Both kinds of swarm-cell have 

 two cilia, or the former in some cases 

 four ; Lagerheim describes, in Conferva 

 bombycina (Ktz.), megazoospores with a 

 single cilium. From each parent-cell are 

 produced either one or two megazoospores. 



In only a few species has the process 

 of conjugation of zoogametes been actually 

 observed, and the systematic position of a 

 large number of the species is therefore 

 at present only conjectural. Areschoug has 

 followed both the conjugation of the zoo- 

 gametes and the direct germination of the 

 megazoospores in Urospora (Aresch.). In 

 Conferva (L.), Chaetophora (Schr.), Draparnaldia (Ag.), and some other 



T 



Fig. 242. — Microspora Jloccosa Thur. 

 A, B, portions of filament. C, fila- 

 ment dividing for the escape of zoo- 

 spores. Z>, zoospores (x 300). 

 (After Cooke.) 



